Materials and devices for energy and environment applicationsE
Self-healing materials – from concepts to market
The ability of a material to show autonomous or activated self-repair is of importance in view of costs, sustainability, and safety. This interdisciplinary symposium will present the latest update on various strategies to induce self-healing in structural and functional materials where damage management and self-repair is of relevance.
For a broad range of applications in various classes of materials, the ability of key components to restore the original properties after local contact, damage or fatigue would represent a promising step towards lower costs and enhanced reliability. The last few years have experienced a strong development of activities in a broad range of materials from polymers to metals, as well in academia as in industrial research. The advancing understanding of the underlying mechanisms has fertilised the development of novel approaches, materials, and synthetic procedures from the scratch. At the same time, existing materials and components were screened and optimized for their ability to self-repair, mainly on a more empirical base. The symposium aims to bring together experts from academia and industry interested in the advancement of self-healing materials, and to foster the emerging activities to transfer promising approaches and findings from the lab to application. The program will cover sessions focussing on the important material classes, including polymers, composites, concrete, ceramics, metals, and functional components, as well as on biomimetic, sustainable and comprehensive concepts, and on transfer activities and market considerations. We cordially invite contributions from all related disciplines, i. e. chemistry, physics, material sciences, engineering, mathematics and biomimetics.
One major task for the symposium is to include contributions of young researchers to encourage and support their scientific career. By emphasizing the multidisciplinary character of the field, we are aiming at an intensive exchange on ideas, concepts, and realizations for the future of self-healing materials. It should be realized that Europe is a key continent in this field with 5 EU funded programs and 4 national research programs as well as a number of more isolated research projects. More than in the previous conferences in the field, we address quantification of healing as well as studies on the underlying physics and chemistries. Also conceptual studies to identify potentially attractive self-healing materials on the basis of their general physical properties are expected.
Hot topics to be covered by the symposium:
- Self-healing polymers (intrinsic and extrinsic approaches, polymer dynamics, elastomers & thermoplastics, coatings & bulk polymers)
- Self-healing reinforced polymer composites (carbon, glass, polymeric reinforcements, (multi)functional fillers, morphology & interaction)
- Self-healing concrete and reinforced compounds (autogenous self-healing, polymeric self-healing, microbial self-healing, modelling, characterization)
- Self-healing ceramics (bulk composites ceramics & ceramic coatings, intrinstic and extrinsic mechanisms)
- Self-healing in metals (creep damage, corrosion)
- Functional components, devices, and applications (catalysts, OLEDs, TIM’s)
- Quantification of self-healing properties
- Novel and biomimetic concepts towards self-healing materials
- Sustainability aspects
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Session 1 : -
Authors : Véronique Michaud
Affiliations : Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Resume : Self-healing materials constitute a dream for many structural engineers, wishing that a given part could detect damage events and mend them to a certain extent during service, by continuously adapting to the changing environment, or by carrying repair fluids to the damaged zone. When considering structural fiber reinforced composites, which are anisotropic and contain a large volume fraction of fibers, typically between 50 and 60%, the damage mechanisms are complex and take place at various scales. The healing system is in general conceived to heal matrix or interface cracks, as fiber damage has not yet been demonstrated. Healing concepts must be designed to act where needed the most, without further disrupting the structural integrity of the part. As a result, self-healing fiber reinforced composites have been demonstrated to a lesser extent compared to self-healing polymers, as they still pose technical and scientific challenges to reach maturity, and to move from basic laboratory concepts on model systems to practical applications. The presentation will review current approaches to develop self-healing composites, considering both extrinsic methods with a repair fluid, and intrinsic methods based on matrix repair, as well as autonomous or assisted healing methods, for example with heat or other external triggers. We will attempt to review and assess the critical hurdles, from scientific to part processing to economical aspects, that remain to be overcome to bring these materials closer to market applications.
Authors : Kazuaki Sanada, Tomonari Suyama, Rikiya Fujisaki
Affiliations : Toyama Prefectural University, Department of Mechanical Systems Engineering Japan
Resume : This study examines the interlaminar shear strength and self-healing of carbon fiber/epoxy laminates fabricated by a tow-spreading technology. Healing is accomplished by incorporating a microencapsulated healing agent and catalyst within a polymer matrix. Self-healing is demonstrated on short beam shear specimens of carbon fiber/epoxy laminates and the healing efficiency was evaluated by the strain energies of virgin and healed specimens. The effect of microcapsule concentration on the interlaminar shear strength and healing efficiency is discussed. The damage area of the healed specimens was also examined by an optical microscope. As the microcapsule concentration increased, the healing efficiency increased and the interlaminar shear strength decreased. Moreover, the change of damage progression path of the each specimen caused a large scatter in the healing efficiency.
Authors : Patryk Adam Jarzynka; Ian P. Bond, Duncan F. Wass
Affiliations : University of Bristol, Department of Aerospace Engineering, United Kingdom
Resume : Carbon fibre reinforced polymer (CFRP) composites are of great interest in aerospace, defence and automotive industries due to their exceptional specific mechanical properties. Composites subjected to long-term service conditions are susceptible to damage, including matrix cracking, crack propagation, delaminations etc. Undetected and not repaired, damages lead to composite degradation and premature failure of the component. However, composites can now be designed to heal autonomously through embedded microcapsules, vascular networks and intrinsic self-healing systems. The purpose of this research is to put into action an autonomous capsular self-healing system in a high performance carbon fibre reinforced polymer (CFRP) composite. It involves the design of a capsular healing system, manufacturing of a composite structure and tests for its healing performance. The chemistry of epoxy resins and a solid state catalytic curing agent was selected and evaluated. Chemistries were then embedded in the interleave region in flat laminates. Composites for these purposes were manufactured using standard processing techniques (hand lay-up, out of autoclave curing). The healing efficiency was investigated using Mode I fracture methodology using a modified double cantilever beam (DCB) test specimens. Additionally, an extensive study was undertaken to determine and minimise the detrimental effect of microcapsules on a unidirectional CFRP. This effect was quantified using short beam shear methodology. It is demonstrated that autonomous capsular self-healing can be achieved in unidirectional CFRP composites. Ruptured microcapsules release the contained liquid epoxy resin, which upon contact with dispersed catalytic curing agent, polymerises and bonds delaminated surfaces. There are many issues associated with inclusion of fragile microcapsules and catalyst particles in the composite structure. With the findings in this investigation, provide a new insight and knowledge in capsular self-healing and its application in high performance fibre reinforced structures is discussed in detail.
Session 2 : -
Authors : W.G. Sloof
Affiliations : Delft University of Technology, Department of Materials Science and Engineering,Netherlands
Resume : In a large European research project called SAMBA, industry and universities work together on the development and improvement of a unique self-healing thermal barrier coating (TBC). A TBC is applied in gas turbine engines for propulsion and electric power generation. Such ceramic coating enhance the gas turbine engine efficiency by allowing higher operation temperatures, saving fuel and reducing CO2 emissions. By using self-healing thermal barrier coatings, small cracks in the coating are repaired, thereby prolonging the lifetime of the coating by 20-25% and significantly reducing the costs of maintenance. The new ceramic coating consists of a layer of yttria-stabilized zirconia, including small particles consisting of molybdenum and silicon. Addition of these small particles allows for self-repair of the coating. Upon fracture, the silicon is oxidized and fills the crack with silicon oxide. Subsequently, the silicon oxide reacts with the ceramic coating layer and creates a stable filling of the crack. This new, innovative self-healing concept will be realized through a combined theoretical, experimental and modelling approach. The project will be carried out by Delft University of Technology and her partners, which include Forschungszentrum J?lich, University of Manchester, Institut National Polytechnique de Toulouse, Research Center RSE in Italy, Flame Spray Technologies in the Netherlands, Alstom Switzerland and GKN Aerospace in Sweden.
Authors : W. Nowak , A.L. Carabat, W.G Sloof , D. Naumenko, W.J. Quadakkers
Affiliations : Institute for Energy and Climate Research, IEK-2, Forschungszentrum Jülich GmbH, 52425, Jülich, Germany;Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD, Delft, The Netherlands
Resume : Internally cooled components in the hottest parts of gas turbines are protected using ceramic Thermal Barrier Coating (TBC) systems. Commonly, the TBC is made of Yttria Stabilized Zirconia (YSZ) and applied by Air Plasma Spraying (APS). Long term turbine operation including temperature cycling results in crack formation in the ceramic topcoat eventually followed by its failure. A self-healing TBC system is being developed in the EU funded project SAMBA to prolong the lifetime. As healing agent fine particles of MoSi2 are proposed, which will react with the YSZ thereby filling the cracks induced by thermal stresses. To improve crack filling properties, B is added to the MoSi2-based particles, while addition of Al is necessary to encapsulate the particles with an Al2O3-scale to prevent their decomposition during coating spraying and to prevent premature reaction with YSZ during the early stages of service. In the present study the oxidation behaviour of MoSi2-based particles with various B and Al contents was studied between 900 and 1100 °C up to 500 h in various atmospheres. The particles after oxidation were investigated using X-Ray diffraction, optical and scanning electron microscopy. The studies revealed that the oxide scale formation strongly depends on the B and Al-contents as well as particle size and exposure conditions. Based on the obtained results an optimized heat-treatment procedure for particle encapsulation prior to spraying or in-situ is being developed.
Authors : Vimal Saini, Max Von Tapavicza, Anke Nellesen, Annette Schmidt, Katrin Braesch, Christina Eloo Holger Wack
Affiliations : Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT, Osterfelder Str. 3, 46047 Oberhausen, Germany Institute of Physical Chemistry, University of Cologne, Luxemburger Str. 116, 50939 Köln, Germany
Resume : Corrosion of metals is a serious problem in the material science. The most common approach for corrosion control is to apply protective coatings on metal substrates. However as the outmost layer on metals, protective coatings face high risk of being damaged or scratched originally at micro-level during transportation, installation and service. Due to this damage, corrosive species can freely reach to the metal surface, thus initiating corrosion and breakdown of the coating. The goal of this research therefore is to use the self healing approach to increase the lifetime and corrosion protection of a coating. For this purpose, swellable yet dried hydrogel particles are incorporated into the coating. These hydrogel particles swell to a large extent when they are in contact with water. In the vicinity of a crack, the gel particles become accessible by the water, absorb and swell it to blocks the gap against diffusion of adjacent corrosives and therefore protect the substrate against corrosion. A range of coatings based on epoxy powder are prepared. Various concentrations of swellable hydrogels in the range from 10%-50% are incorporated in the coatings. The corrosion performance of coatings are evaluated with the help of electrochemical impedance spectroscopy (EIS). EIS result shows the increase in the impedance modulus and polarization resistance over a period of time indicating the corrosion inhibition capability of the coatings.
Authors : Y. Zhang,C. Rocco,F. Karasu, L. G. J. van der Ven, R. A. T. M. van Benthem, X. Allonas,C. Croutxé-Barghorn, A. C. C. Esteves, G. de With
Affiliations : Laboratory of Physical Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; University of Haute Alsace, Mulhouse, France; Dutch Polymer Institute, Eindhoven, The Netherlands; DSM Ahead BV, Geleen, The Netherlands
Resume : Most hydrophobic coatings are vulnerable to maintain the hydrophobicity upon surface damage, due to the loss of the hydrophobic chemical groups. Thus, the concept of self-restoring hydrophobic functionalities on polymeric surfaces, by replenishing the functional groups on the damaged surfaces, is of high interest. The proof-of-principle of self-replenishing hydrophobic surfaces was reported earlier for a Polyurethane-based cross-linked network with a small amount of fluorinated dangling chains. In these systems the dangling chains can re-orient to the new surfaces created upon damage. However, the drawbacks identified for this system restrict its direct industrial application: 1) cross-linking needs a high temperature treatment and a long procedure, 2) the use of fluorinated materials is undesirable due to environmental concerns and 3) these systems have low hardness, due to low Tg. We present new, more cost/energy-effective self-replenishing coatings, which were prepared by incorporating methacrylate-ended fluorinated dangling chains into PEG-diacrylate-based networks via UV-initiated radical polymerization. These coatings exhibit multiple self-replenishing ability of the surface hydrophobicity after damage. We will discuss how the network architecture and UV-curing process influence the self-replenishing behavior. The first results on self-replenishing systems based on more environmental-friendly PDMS low surface energy chemistries will also be presented.
Session 3 : -
Authors : Virginie Wiktor
Affiliations : Section of Materials and Environment, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands
Resume : The presence of cracks is a major limitation upon the durability of concrete structures as it can lead to the premature corrosion of the reinforcement, resulting in costly measures of maintenance and repair. In that respect, the development of bio-based self-healing mechanism which autonomously repairs formed microcracks is of great interest. In this type of concrete particles featuring specific bacteria and feed are directly added to the concrete mixture. Upon crack formation the bacteria and feed are released from the particle by crack ingress water. Subsequent bacterially mediated calcium-based mineral formation results in the physical closure of the crack what delays further ingress of water and aggressive corroding substances. This paper presents the recent advances on the development of the bacteria-based system in order to allow full-scale outdoor applications. Besides optimization of the healing capacity, another aspect concerns technical developments for large scale and economic production of the bacteria-based systems. Laboratory results quantitatively showed that the crack-healing capacity of bacteria-based self-healing concrete is significantly improved compared to normal concrete as the maximum healable crack width more than doubled. This is of particular interest when addressing the reduction of maintenance and repair costs. A repair system based on the basic idea of the bio-based self-healing concrete has also been developed. Its application in the laboratory but also outdoor on real concrete structure showed great potential for the sealing of cracks. Based on these promising results and growing interest from companies in this novel technology, a spin-out company, Green Basilisk, has recently been created with the aim to further develop and bring the bacteria-based systems to the commercialization phase.
Authors : Petros Giannaros, Prof. Abir Al-Tabbaa
Affiliations : University of Cambridge Department of Engineering
Resume : Autonomic self-healing of concrete can be achieved using microcapsule admixtures. Crack propagation within the concrete ruptures embedded microcapsules. As a result, the microcapsules provide healing by releasing their contents into the crack volume. Healing of cracks is highly desirable from a durability perspective as cracks facilitate the flow of aggressive substances into concrete. This corrodes the steel reinforcement and compromises structural integrity. Ideally, microcapsule addition will not affect initial concrete properties. The enhancement brought about from microcapsule addition is only realised after damage has occurred. In this work, several microcapsules that vary in size, as well as shell and cargo material, were characterized and then added to cement at varying volume fractions. In this way, the relationship between microcapsule fraction and compressive strength was investigated. Survivability during mixing and rupture of the capsules upon crack propagation was confirmed using both optical and scanning-electron microscopy. It was found that, at small volume fractions, microcapsule addition can increase the compressive strength of cement paste. Increase in microcapsule volume fraction past a threshold will result in a decrease in strength. Further work is being carried out to quantify the effect of microcapsule addition on the mechanical properties of mortar. The efficacy of the microcapsules to provide crack sealing and healing is also being investigated.
Authors : Benoit Hilloulin, Frederic Grondin, Ahmed Loukili, Nele De Belie
Affiliations : LUNAM University, Institut de Recherche en Genie Civil et Mecanique (GeM), UMR-CNRS 6183, Ecole Centrale de Nantes, 1 rue de la Noe, 44321 Nantes, France; Magnel Laboratory for Concrete Research, Ghent University, Technologiepark Zwijnaarde 904, B-9052 Ghent, Belgium
Resume : Concretes intrinsic ability to heal, called autogenic healing, has been reported for many years. However, a deeper understanding of the natural phenomenon could help design innovative healing solutions based on cementitious materials themselves. In this study, natural self-healing potential of cementitous materials is studied through experimental works, based on three-points-bending tests of mortar specimens, microscopic observation of cement pastes using scanning electron microscope (SEM) with energy dispersive spectrometry (EDS) and microindentation tests performed around the crack or on the healing products. The influence of various parameters (e.g. healing time, initial crack width, age at cracking and water-to-cement ratio) has been investigated. Small cracks with a width of around 10 ?m can quickly heal within several days by immersion into water. Mechanical regain up to 80 % of an uncracked specimen is observed for several water-to-cement ratios and is proportional to the initial crack width and mainly depends on the age at cracking. These mesoscopic results are confirmed by the development of healing products at microscale: calcium silicate hydrates, portlandite and ettringite, which can growth very quickly when a narrow crack is created at early age. SEM and EDS analysis revealed the porous aspect of the CSH created inside the crack which can explain their relatively poor mechanical properties. Microindentation tests established a weak bonding between portlandite created inside the crack and the crack lips which can lead to the brittle behaviour of healed mortar specimens. Moreover, mechanical properties around the crack are lower than the ones inside the matrix.
Poster Session I - incl. 3 min Poster Presentation : -
Authors : A. Shaaban, N. Hohlbein, A. M. Schmidt
Affiliations : Department für Chemie, Universität zu Köln, Luxemburger Str. 116, D-50939 Köln, Germany
Resume : The research interest on remote-controlled multiple responsive materials has increased over the last few decades. Magnetic nanoparticles have the potential to convert magnetic energy of external alternating fields into thermal energy. The combination of magnetic nanoparticles with soft materials offers new possibilities towards smart adaptive materials that can be manipulated by external magnetic fields. In particular, the local heat dissipation by magnetic nanostructures in oscillating electromagnetic fields (OEMF) provides the option to increase the temperature locally and thus stimulate dynamic processes, e. g. for self-healing. In this work, we systematically investigate the influence of the size, shape, composition and magnetocrystalline anisotropy of the magnetic nano-antennas in an acrylate-based ionomeric elastomer on the heating and healing characteristics. Furthermore the influence of the particle on the dynamic and mechanical properties of the used ionomers is taken into account. The locally dissipated thermal energy in the particles environment triggers a thermal transition in dynamic polymeric matrices activating the self-healing process. In comparison to known thermally activated systems, the incorporation of nanoscopic heat sources leads to a faster response and allows the contactless, remote-controlled triggering of the sample shape. Under optimized conditions, a particle volume fraction as low as 0.05 vol% is sufficient to reach a healing efficiency of 90 % and higher after 15 min of irradiation.
Authors : Simone Bonetti, Matteo Farina, Michele Mauri, Kaloian Koynov, Hans-Jürgen Butt, Michael Kappl, Roberto Simonutti
Affiliations : Materials Science Department, University of Milano-Bicocca, Via R.Cozzi 55 20125 Milan,Italy; Max-Plank-Institut für Polymerforshung, Ackermannweg 10 55128 Mainz, Germany
Resume : Degradation, damage and failure must be faced in any material application. Within the material formulation self-healing additives improve reiliability and duration of products, enhancing the customer-perceived quality and value. Here the synthesis and characterization of Poly(n-butylacrylate)/Polystyrene nanoparticles (PBA/PS NPs) as potential capsule-based healing system are presented. PBA/PS NPs indeed combine the adhesive properties of PBA with the structural stability and low cost per unit weight of PS. The NPs are prepared via semicontinous miniemulsion polymerization, easy to scale-up and performed with eco-friendly solvents (i.e. water). Dynamic Light Scattering is used to monitor the PBA core formation and the PS shell growth, while the NPs morphology is studied via SEM and AFM. Composition and local mobility of the system are probed with Solid state NMR (TD-1H-NMR, CP-MAS and SPE 13C-NMR). All the data fit a morphological core-shell sharp interface model, demonstrating the sequestration of the PBA core into the PS shell and probing that the peculiar mobility of each phase is preserved. Single particle nanomechanics is performed with AFM force spectroscopy: a controlled increase in the external force acting on the NP triggers the plastic deformation of PS shell; a futher increment leads to the ultimate NP baroplastic collapse. AFM images monitor the mechanism of the NP breakdown, while force spectroscopy simultaneously allows the estimation of the forces involved.
Authors : T. Mes, A.W. Bosman
Affiliations : SupraPolix
Resume : Supramolecular polymers using hydrogen-bonding interactions between the macromolecules are eminently suitable as self-healing materials. The quadruple hydrogen bonding ureidopyrimidinone (UPy) unit is a particularly effective and versatile design motif for this. Due to the sensitivity of hydrogen bonding to temperature, concentration and to the environment, the hydrogen bonds are continuously formed and broken. By tuning the equilibrium of open and closed hydrogen bonds, self-healing behavior can be obtained as an intrinsic material property without the need of any external stimulus or the inclusion of chemicals, catalysts, or plasticizers. Self-healing can be obtained by the incorporation of UPy motifs into a broad range of polymer backbones on an industrial scale. The necessary chemistry is highly compatible with commonly used polymer chemistry, resulting in a wide variety of polymers with self-healing properties, such as hydrogels, polyurethanes, poly(meth)acrylates and polysiloxanes. Self-healing cycles can be repeated over and over again as no material is consumed and furthermore, the thermo-reversible nature of UPy-based self-healing materials allows thermal processing methods like extrusion. In this presentation, supramolecular polymers modified with the UPy-unit will be presented, and their self-healing applications related to aeronautical composites, biomedical applications, coatings, and prototyping, will be highlighted and discussed
Authors : Niels Van Herck, Duchan Laplace, Filip E. Du Prez
Affiliations : Ghent University - Polymer Chemistry Research Group, Belgium
Resume : Throughout the years, self-healing has become a broad and important research field within polymer chemistry. However, the majority of existing polymer systems focus on the repair of damage on the submicron scale, which leads to inadequate healing when a large-volume damage site is created. The deficiency of these polymer systems to heal damage on the macro scale is a consequence of mainly two issues, being the limited volume of healing agents and the inability to reunite the crack edges. In 2014, White et al. (Science) proposed a vascular two-stage polymer system for the restoration of large-scale damage, thereby broadening the limits for damage repair. However, the difficult architecture hinders direct implementation in any commercial industrial process and simpler concepts are desired. In 2014, Rivero et al. (Macromolecules) proposed a polymer system for the healing of polyurethanes upon heating, using a combination of shape-memory and reversible furan-maleimide chemistry to reunite and repair crack edges. Although good mechanical properties were obtained after healing, the time needed for healing (12h at 50°C) is susceptible for improvement. In this project, the slow furan-maleimide chemistry is replaced with the ultrafast triazolinedione (TAD) chemistry (Billiet et al., Nat. Chem.) in order to reduce the healing time. In addition, sonochemistry experiments are presented to confirm mechanical breaking of the reversible TAD-indole bond, which is vital for efficient healing.
Authors : A. M. Grande, R. Martin, J. Bijleveld, I. Odriozola, S. J. Garcia, S. van der Zwaag
Affiliations : Novel Aerospace Materials, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, the Netherlands; Materials Division, IK4-CIDETEC Research Centre, Paseo Miramón 196, 20009, Donostia-San Sebastián, Spain
Resume : In the last decade, significant efforts have been made by the chemistry community to research and synthetize new elastomeric materials with self-healing functionality. Although several chemical concepts have been proposed no commercially available material has been reported combining both high mechanical properties and a substantial healing efficiency. To date, healable polymers based on polysulphide linkages are promising systems to reach the market level, however a low understanding of the true interfacial healing potential of these new materials is reported. In this research, a poly(urea-urethane) elastomer incorporating dynamic disulphide bonds is selected to elucidate the different aspects playing a role in the interfacial healing process. Rheological and fracture measurements are performed to achieve a clear understanding of the phenomena involved. While small amplitude oscillatory shear rheometry, allow to identify the main relaxation processes in the polymeric network, a fracture testing procedure based on the evaluation of the critical J-integral is used to investigate and quantify the recovery of the mechanical properties at the repaired interface following healing cycles at different time and temperature. Activation energies for the two studied phenomena (relaxation and healing) are calculated and comparable temperature dependence was found highlighting the direct link between rheological and fracture properties to healing.
Authors : M. Hernández, S.J. García, S. van der Zwaag
Affiliations : Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
Resume : Healing of local mechanical damage is especially challenging in vulcanized rubbers, where the confinements imposed by the high density of cross-links restrict polymer chains to diffuse and form new bonds across former (pre-) fractured surfaces. In this research, interfacial healing was achieved in conventionally sulfur-cured natural rubber (NR). NR compounds were prepared and vulcanized at different temperatures and times, such that the potential influence of sulfur bonds on the healing properties of NR could be evaluated. Circular rubber samples were cut to half of their diameter. Subsequently, the damaged samples were placed in an in-house developed set-up, i.e healing cell, and healed under controlled temperature and pressure conditions enabling chain inter-difussion and/or rebonding of sulfur bonds across the interface. The recovery of the damaged interface was probed by dielectric spectroscopy measurements, revealing the molecular dynamics involved in the healing process. The segmental relaxations of the pristine, damaged and healed samples were compared. It was found that the dynamics of the NR compounds changes with the degree of curing, while healing is only achieved at curing degrees lower than 50%. A new correspondence between the relaxation times of pristine and healed samples was observed; the parameters derived from the Havriliak-Negami fitting of the relaxation times indicate that locally a more heterogeneous structure is formed in the rubber during the healing.
Authors : X. Tsilimigkra , A. Baltopoulos, S. Tsantzalis, A. Kotrotsos, E.Giannaros, V. Kostopoulos
Affiliations : Applied Mechanics Laboratory, Department of Mechanical Engineering & Aeronautics, University of Patras, Patras University Campus, GR 265 00 Patras, Greece
Resume : In the area of self healing materials,tapered double-cantilever beam (TDCB) has been widely adopted along literature for measuring the recovery rate between the virgin and the healed material,in terms of the inherent material property of fracture toughness.In house work on TDCB with self healing functionality pointed out that the propagating crack exhibited a tendency to deviate considerably from the centre-line,resulting in arm breaking.In light of this issue,a modified configuration of the existing Compact Tension(CT) specimen was investigated.The main concern was to avoid the sudden catastrophic failure which is expected in brittle materials and prevents the healing efficiency study. Thus,efforts are towards introducing CT specimen,with a drilled hole along the centerline of the crack tip as crack stopper.Potentially, the modified specimen would arrest the crack at the introduced drilled hole and allow the crack to be healed and tested again at the same conditions. A numerical study has been carried out using finite element analysis.Several cases were analyzed regarding two main parameters:the hole distance from the crack tip and the its diameter.The criterion for selecting the proper location is the stress distribution around the hole.Validation against experimental results confirmed the hole effectiveness.Adopting the developed geometry,tests on CT specimens were performed,containing capsules filled with the healing agent,in order to confirm the self healing functionality
Authors : Wataru Nakao, Shunsuke Yoshioka, Teturo Yanaseko
Affiliations : Yokohama National University, Faculty of Engeneering Division of Materials Science and Chemical Engineering, Japan
Resume : Self-healing materials for high temperature use needs advanced material design using backcast on the applications, because self-healing materials exhibit the functions using chemical reaction and chemical reactions often affect strongly the surrounding temperature. Thus, in order to develop the available self-healing ceramics, chemical reaction inducing the self-healing function should be adjusted to be suitable for the service conditions of the application. Furthermore, adequate arrangement of the healing agent in the material is important to maximize the chemical reaction effect to strength recovery behavior. Based on the above concept, fiber-reinforced self-healing ceramics was developed to be available to the turbine blade of jet engine. Thus, the heterogeneous layer consisting of TiSi2 and SiC was employed as the healing agent to adjust the available healing temperature to service temperature. Moreover, the healing agent was arranged at only the interlayer between ceramic fiber bundle and ceramics matrix. The above materials design produces the high active self-healing behavior, by which the introduced cracks was completely re-bonded at 1000 oC for 10 min, and the self-healing function is enough high to apply the middle pressure turbine blade.
Authors : P.J. Antunes, A. M. Grande, A.M. Moura , S. J. Garcia, J. C. Viana, S. van der Zwaag
Affiliations : Critical Materials S.A., Avepark - Science and Technology Park, 4805-017, Guimarães, Portugal; Novel Aerospace Materials group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, The Netherlands
Resume : In recent years self-healing polymers have become an attractive and challenging research topic. Researchers have developed intrinsically self-healing polymers and elastomers which are about to enter the market. It is foreseen that designers will soon start to adopt such materials for real-life applications. Hence they will require new numerical tools to predict the damage and healing response of such materials as a function of the mechanical loading history. This contribution presents a numerical framework to evaluate the intrinsic dynamic nature of a supramolecular elastomer with intrinsic self-healing capabilities. First, the viscoelastic behaviour of such a material under small and large uniaxial deformations was studied experimentally for different loading conditions. To this aim, uniaxial tensile tests, as well as stress relaxation and cyclic tensile experiments were performed at different strain rates and maximal strain levels. The response of the material was described by means of hyper-elastic, viscoelastic and damage evolution laws and implemented in a commercial non-linear Finite Element code (Abaqus). The results obtained demonstrate how the complex mechanical response exhibited by the supramolecular elastomer studied can be modelled with conventional constitutive equations. However, a derivative-free global numerical optimisation procedure, based on a FE model-based inverse problem formulation is required to properly extrapolate the various model parameters. The
Authors : Seppe Terryn, Glenn Mathijssen, Joost Brancart, Guy Van Assche, Bram Vanderborght
Affiliations : Vrije Universiteit Brussel (VUB) Robotics & Multibody Mechanics (R&MM) Physical Chemistry and Polymer Science (FYSC), Belgium
Resume : Next generation robots contain an intrinsic compliance, which ensures energy efficiency and safety during interaction with humans and unstructured, dynamic surroundings. A large part of these soft robots move using soft pneumatic actuators, which are entirely constructed out of flexible elastomeric materials and are actuated by compressed air. Although these actuators have the ability to resist mechanical impacts, they are in general susceptible to damages caused by fatigue and by sharp objects found in the unstructured environments. These are damages which can be healed if the actuator is built entirely out self-healing (SH) polymers. This novel feasibility research examines the potential of developing robotic soft pneumatic actuators entirely out of available SH-polymers, making them able to autonomously heal cuts and perforations caused by sharp object. To do so, a single soft pneumatic cell (SPC) was built entirely out of SH-elastomeric polymer. These are dynamic covalent polymer network systems based on the reversible Diels-Alder (DA) reaction between a bismaleimide and a furan 4-functionalized component. Macroscopic damages in these non-autonomous DA-polymers can be healed using relatively low temperatures (< 70°C). Macroscopic damages in the SPC can be completely healed using a SH-procedure and the mechanical properties of the actuator are recovered, proving the potential for further investigation on the use of DA-polymers and other SH-polymers in soft robotics.
Authors : Mikhail Perelmuter
Affiliations : Institute for Problems in Mechanics of the Russian Academy of Science
Resume : The bridged and cohesive crack models are used for evaluation the self-healing efficiency of cracked structures. In the frames of this modeling approach is assumed: there are artificial bonds between crack surfaces (the interface layer); any zone of these bonds is considered as the crack process zone (bridged or cohesive) with distributed nonlinear spring-like ligaments between the crack surfaces. The bonds properties variation define the stress state at the crack process zone and, hence, the fracture toughness of the healed material. The choice of the process zone model (cohesive or bridged) depends on the materials type and self-healing mechanism. The transition between cohesive and bridged models is considered. The main task of the modeling consists in the computational analysis of the stresses distribution in the process zone and in the computing of the stress intensity factors which are the main characteristics of self-healing efficiency. The mathematical background of the stresses problem solution is based on the singular integral-differential equations method and the boundary elements method. Different self-healing methods (microcapsules filled with a self-healing agent, microvascular fibres, mendable polymers) with various mechanisms of self-healing are analyzed. The thermo-fluctuation kinetic model is used to evaluate the regeneration and formation of the crack process zone. The non-local fracture criterion is used to evaluate the fracture toughness and the critical external loading in the frames of the bridged crack model. The model can be use for the evaluation of composite materials healing and durability. Some results of self-healing processes analysis are presented and discussed.
Authors : Juan Yang, Huaitian Bu, Nicolas Rival, Susie Jahren, Christian Simon, Ferdinand Männle, Emmanuel Cailleux
Affiliations : Materials and Nanotechnology Sector, SINTEF, Forskingsveien 1, 0314, Oslo, Norway; CSTC-WTCB-BBRI, Avenue Pierre Holoffe 21, 1342 Limelette, Belgium
Resume : Capsule-based repairing systems are one of the most commonly-used healing materials, where active agents are encapsulated by a polymeric/inorganic shell and released either by external stimuli (temperature, pH etc.) or mechanical force. The polymeric capsules should be able to protect the healing agent for a long time, and release the healing agent when cracking in a matrix material occurs. At the same time, the capsules should not influence the workability of the matrix (for example concrete). To this end, the capsule shells should have good barrier properties against both water vapour and oxygen, certain brittleness to release the healing agent and certain mechanic strength to survive the mixing process. In the present work, functional polyhedral oligomeric silsesquioxane (POSS) hybrid nanomaterials with hydrophobic modification were prepared via a two-step synthesis including a sol-gel process. NMR results showed the formation of amide functionality on the POSS. PET was selected as the polymer system and was blended with different amount of hybrid additives. It was found that the addition of modified POSS nanomaterials (5%) improved the mechanical strength while decreasing the impact strength (increasing the brittleness of PET). Preliminary testing results of the polymer blend indicated an oxygen barrier level which is comparable to unmodified PET, while water transmission rate will be measured. It could be suggested that the polymer blend (PET and the hybrid POSS nanomaterials) is a potentially interesting candidate as capsule wall for encapsulation of healing agents in self-healing concrete. Acknowledgement The research is supported by Research Council of Norway via the European research project CAPDESIGN Encapsulation of polymeric healing agents in self-healing concrete: capsule design through EU funded network M-era.Net program (Project number 233018/O70)
Authors : Joost Brancart, Maria Mercedes Diaz Acevedo, Jonas Van Damme, Otto van den Berg, Guy Van Assche
Affiliations : Physical Chemistry and Polymer Science, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, België; Polymer Chemistry Research Group, Universiteit Gent, Krijgslaan 281 S4-bis 9000 Gent, Belgium
Resume : Research in the field of smart materials that exhibit self-repair mechanisms has greatly expanded over the last few years. This is especially true for polymers and polymer composite materials. Reversible polymer network systems that use dynamic covalent bonds as a means to repair sustained damage are one of these smart polymer systems. Currently a range of different dynamic covalent bonds is considered, of which the reversible Diels-Alder chemistry has drawn most attention. Reversible covalent bonds have been successfully incorporated into polymer network structures based on the Diels-Alder reaction between a furan and a maleimide. Also photoreversible covalent bonds, such as the photoreversible dimerization of substituted anthracene functional groups, have drawn a lot of attention for various applications, including self-healing coatings. The reversibility of both types of dynamic covalent systems is studied using various spectroscopic and thermal analysis techniques. The self-healing properties are assessed using Atomic Force Microscopy. Different types of defects of controllable size and geometry are created using the nano-lithography option and then healed using in-situ heating.
Authors : Seyed Hosein Payandeh GharibDoust, Parinaz Jafarzadeh, Sepideh Khoee
Affiliations : Department of Chemistry, Tehran University, P.O.Box 14155-6455 Tehran, Iran
Resume : Key words: self-healing, response surface methodology, epoxy resin, nanocapsule, urea formaldehyde. Inspired by living systems, self-healing polymers are designed to automatically repair damages in coatings and composites, thus providing a means to significantly extend the service life and reliability of polymeric structural composites. It has been shown that micro/nanocapsules embedment is among the most successful approaches to provide self-healing ability in polymers . Here a model is provided that demonstrate the effect of different synthesis parameters on the properties of nanocapsules containing epoxy resin. The most effective parameters on the properties of nano-capsules such as surfactant concentration, agitation rate and sonication time are selected and the response surface method is used to determine the effect of these parameters on the nanocapsules size and core content. Using the modified variables, nanocapsules with a size of 165 nm and a core content of 68.7% are prepared. Thermogravimetric analyses reveal that the nanocapsules are stable up to 200 °C which makes them applicable for future wide spread use in self-healing coatings and composites.  H. Wei, Y. Wang, J. Guo, N.Z. Shen, D. Jiang, X. Zhang, et al., Advanced micro/nanocapsules for self-healing smart anticorrosion coatings, J. Mater. Chem. A. 3 (2015) 469480. doi:10.1039/C4TA04791E.
Authors : Ragnhild Hancke , Wen Xing, Zuoan Li, Marie-Laure Fontaine, Mtabazi Sahini, Tor Grande, Truls Norby
Affiliations : University of Oslo; SINTEF Materials and Chemistry; Norwegian University of Science and Technology
Resume : Gas separation technologies making use of robust and efficient ceramic mixed conducting (oxide ion/proton and electron) membranes are expected to contribute to significant cost reduction and higher efficiency of carbon capture and storage in power production and industrial processes. Finding materials which combine high flux density with long term stability is the major hindrance for developing better ceramic gas separation membranes. Instability arises from thermal stress and materials creep in the chemical gradient, resulting in leakages and membrane failure. This causes the breakdown of entire modules whose replacement is complex and expensive. On these bases, self-healing ceramic membranes with increased robustness and lifetime will be a major breakthrough in the development of ceramic membranes for gas separation technology. In the Norwegian funded SEALEM project we are investigating several self-healing concepts which will give ceramic membranes an inbuilt healing ability. The membranes are fabricated with architectures consisting of a stacking of porous and dense layers with various materials composition. These architectures are designed so that whenever a crack or pinhole occurs across the dense membrane, the difference in chemical potentials on either side of the membrane initiates the repair mechanisms. We have, as of today, tested the concept on a number of materials combinations, enabling identification of a set of system requirements for a successful repair.
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Session 4 : -
Authors : Costantino Creton, Koichi Mayumi, Thomas Guyon, Tetsuharu Narita, Chung Yuen Hui, Jingyi Guo
Affiliations : ESPCI ¨Paris Tech, 10 Rue Vaquelin, 75231 Paris Cedex 05, France; Cornell University, Mechanical and Aerospace Engineering, USA
Resume : It has been well established that combining self-healing bonds with permanent bonds, can significantly increase the fracture toughness of soft hydrogels. Yet the details of how this actually occurs and in particular the link between bond breaking and healing dynamics and fracture properties, is not yet known. In this work we investigate in detail the rheology in small and large strain and the fracture behavior of a model hydrogel based on polyvinyl alcohol crosslinked both chemically with glutaraldehyde, and physically with a borax solution. We carried out a series of crack propagation experiments on prenotched gel samples over a wide range of loading rates and measured both the critical energy release rate where the crack propagates, and the average crack propagation velocity for each case. Using a recently proposed 3D mechanical model to describe the breaking and healing of the reversible bonds we can simulate the energy stored and dissipated ahead of the crack and we attempt to explain quantitatively how the physical bonds affect the fracture process of the hybrid hydrogels.
Authors : Roberto Martin, Alaitz Rekondo, Alaitz Ruiz de Luzuriaga, Germán Cabañero, Hans J. Grande and Ibon Odriozola
Affiliations : Materials Division, IK4-CIDETEC Research Centre, Paseo Miramón 196, 20009 Donostia-San Sebastián, Spain
Resume : The introduction of dynamic (covalent 1,2 and supramolecular 3) bonds into polymer systems has been recently used as a powerful approach towards the design of intrinsically self-healing materials. The idea is to reconnect the bonds which are broken when a material fractures, restoring the integrity of the material. This dynamic self-healing approach based on reversible links has been applied using both covalent chemistries and supramolecular interactions. In this sense, the rich chemistry of sulphur offers unique possibilities for the design of reversible interactions. Here we describe different polymer systems, all based on sulphur chemistry, which have been designed to have reversible crosslinks: i) a polyethylene glycol (PPG) hydrogel crosslinked by disulphide bonds and gold thiolates; ii) a poly(urea-urethane) elastomer crosslinked by aromatic disulfide bridges, and iii) a silicone elastomer crosslinked by Ag nanoparticle/thiol interactions. References: 1) P. T. Corbett, J. Leclaire, L. Vial, K. R. West, J. L. Wietor, J. K. M. Sanders and S. Otto, Chem. Rev., 2006, 106, 36523711. 2) S. J. Rowan, S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders and J. F. Stoddart, Angew. Chem., Int. Ed., 2002, 41, 898952. 3) L. R. Hart, J. L. Harries, B. W. Greenland, H. M. Colquhoun and W. Hayes, Polym. Chem., 2013, 4, 48604870.
Authors : N. Hohlbein, A. Shaaban, A. M. Schmidt
Affiliations : Department für Chemie, Universität zu Köln, Luxemburger Str. 116, D-50939 Köln, Germany
Resume : The development of self-healing mechanisms that allow the repair of elastomers instantaneously on the molecular level is highly demanded in order to result in more reliable and durable elastomers. Ionomeric materials that are crosslinked exclusively by dynamic bonds are recently shown to be of potential for autonomous or on-demand self-healing in flexible polymeric materials. In this respect, the use of ionomers represents a promising approach. The strong interaction between ionic moieties within a non-polar matrix leads to microphase separation in a thermally reversible network. The long lifetime of the ionic association and the temperature-reversible formation of ionic cross-links is an essential feature for the ability of intrinsic self-healing. The implementation and parameter optimization, however, requires a profound understanding of the structure-property relationships. For this purpose, we developed a model system for self-healing ionomeric elastomers that allows a detailed insight into the interrelations of molecular structure, ion fraction, counter-ion nature, and the resulting mechanical and self-healing properties. Our results deliver a clear indication for the important impact of the inner structure of ionomer-based elastomers on their mechanical properties, both on their frequency-dependent, dynamic behavior as well as on their thermal characteristics, and that both parameters are essential for the self-healing ability and material reliability in these materials. The self-healing efficiency of the model ionomers is evaluated by tensile tests on macroscopically cut and healed samples. The damaged samples are healed under different thermal conditions and time ranges. The results clearly illustrate the principal potential of ionomers for the development of self-healing materials, and that an optimization of the self-healing effect with respect to the counter-ion nature and the ion fraction is possible.
Session 5 : -
Authors : Yusuf Çağatay Erşan, Nele De Belie, Nico Boon
Affiliations : Ghent University,Magnel Laboratory for Concrete Research,Technologiepark Zwijnaarde 904,B-9052 Ghent, Belgium; Ghent University, Laboratory of Microbial Ecology and Technology (LabMET) Coupure Links 653, B-9000 Ghent, Belgium
Resume : Repair of the concrete cracks is essential to prevent the corrosion of the steel reinforcement and increase the durability of the structure. Recent studies focused on development of self-healing mechanisms to replace the extrinsic maintenance. One of the strategies is the use of bacterial healing agents to induce CaCO3 precipitation in the crack. So far, as a healing agent, axenic cultures have been proposed. Yet, non-axenic cultures can be advantageous by their enhanced performance and resilience. In this study, we compared the self-healing performances (crack width range 200 600 µm) of mortar prisms containing either an axenic denitrifying culture, or a non-axenic denitrifying culture named activated compact denitrifying core (ACDC). Granular activated carbon (GAC) (0.5 -2 mm) was used as protective carrier to incorporate Diaphorobacter nitroreducens cells into the mortar. ACDC particles, due to their self-encapsulated structure, were added into the mortar mix without using any additional protective carrier. After 4 weeks immersion in water, GAC protected axenic culture induced crack closure up to 350 µm while addition of ACDC provided self-healing of cracks up to 500 µm. Microbial healing could be distinguished from autogenous healing by formation of CaCO3 minerals on the inner crack surface and traces of bacterial healing agents on these minerals. Compared to autogenous healing of 450 µm crack, healing by means of ACDC and Diaphorobacter nitroreducens reduced water absorption of prisms by 60±6 and 32±4 %, respectively. The non-axenic ACDC culture appears to supersede the axenic cultures in development of microbial self-healing concrete by avoiding the need for protective carriers and improving the self-healing capacity.
Authors : Amir Tabaković, Wouter Post, Santiago Garcia, Erik Schlangen
Affiliations : Delft Technical University, The Netherlands
Resume : When the cracks within the surface layer of the asphalt pavement are still in an early phase, it is possible to spray a rejuvenator over the surface of the asphalt pavement to prevent further crack propagation and pavement failure. Rejuvenators are engineered cationic emulsions containing maltenes and saturates. Their primary role of a rejuvenator is to reduce the stiffness and restore the viscoelastic properties of the oxidized asphalt binder. Such a process may increase the life span of the asphalt pavement by several years. However, this method only impacts on the top centimetres of the pavement, cracks originating at the bottom of the asphalt layer will not be healed. The inclusion of encapsulated rejuvenators into the asphalt pavement mix presents the potential for overcoming these problems to heal the entire pavement. The principle behind this approach is that the fracture energy at the tip of the cracks generated in the pavement will break open the capsules, and release the contained rejuvenator. The rejuvenator will then diffuse within the asphalt binder, thereby sealing the crack and preventing its further propagation. This work proposes the use of compartmented sodium alginate fibres as a new method for incorporating rejuvenators into asphalt pavement mixtures. Such an approach can potentially offer advantages over spherical microcapsules, such as: alginate is an organic material and poses no environmental/leaching risks, due to the high aspect ratio of the compartments in the alginate compartmented fibres there is a higher potential that the containers will encounter a fracture, while at the same time locally releasing higher amounts of healing agent (i.e. rejuvenator), if not opened via fracture contact, alginate fibres will degrade over time, releasing the healing agent rejuvenator and presenting a secondary self-healing trigger mechanism. This work presents the proof of concept of the encapsulation process, embedding of the fibres in asphalt mixtures and the survival rate of fibres in the asphalt mixture and healing events obtained using such concept. The research findings support the potential for compartmented sodium alginate fibres to contribute to the further development of self-healing asphalt pavement systems.
Authors : P. Minnebo; E. Tsangouri, K. Van Tittelboom, D. Van Hemelrijck
Affiliations : Vrije Universiteit Brussel (VUB), mechanics of materials and constructions (MEMC), Belgium; Unversiteit Gent (UGent) Magnel Laboratory for concrete research, Department of structural engineering, Belgium
Resume : Concrete is a material which is very susceptible to cracks, these cracks (however harmless or tiny they may seem) enable liquids and gasses to potentially reach the steel reinforcement. It should at all times be avoided that this reinforcement can corrode since this entails structural problems. The concept of autonomous self-healing concrete by embedding capsules or tubes into the concrete matrix can heal cracks. The first goal should be to fill the cracks, a second goal is that these cracks are also repaired and mechanical properties are regained (or even increased). The ultimate goal of developing self-healing concrete is to increase the life-time of concrete structures which leads to increased sustainability and reduced cost of repair and maintenance. As stated in literature, lab conditions differ drastically from real conditions, e.g. with respect to casting of the concrete and the care of placing the self-healing system. Meanwhile it became also clear that glass, is not a suitable encapsulation material. This is because unwanted alkali-silica reactions occur, which cause degradation of the concrete and of the self-healing system. Alternative materials to glass should be investigated. These materials should possess the following properties: brittle behavior, resistant to humid conditions, contain the healing-agent, minimal chemical interaction with the healing-agent, good adhesion with the surrounding cementitious material, no degradation of the capsule in time, resistant to the concrete mixing process and a minimal fabrication cost. The advantage of capsules is that they can be distributed in the concrete volume and could ultimately simple be added to the concrete mix. However, enough capsules should break to release enough healing agent to repair the crack and the capsules should survive the concrete mixing process. The advantage of working with tubes is that much more healing agent can be provided once a tube is cracked and that the tubes can be placed very efficiently in the tensile zones. However, placing of these tubes and make sure that they dont break when the concrete is poured still remain a challenge. Proposing and testing of solutions to these problems are described in this work. The proposed solutions are, to design more robust capsules or protect the capsules with an additional coating or material and to design tubes whom deflect the impact when the concrete is casted or protect the tubes with something (e.g. the reinforcement) above it. All of this is done taken into account material parameters and shape. This text presents options to take self-healing using capsules and a vascular system to real scale by considering shape and material parameters to make these systems survive the concrete mixing and casting. A better understanding of this will lead us one step closer to take self-healing concrete to the market.
Authors : Livia Souza, Dr. Antonis Kanellopoulos, Prof. Abir Al-Tabbaa
Affiliations : Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom
Resume : Self-healing cementitious materials are a class of smart materials aimed at the passive repair of minor damage without the need of external intervention. To achieve this goal, one promising and versatile strategy relies on the incorporation of microcapsules filled with healing agent into the matrix: when a crack propagates, it ruptures the microcapsules and releases the healing agent into the damaged area. Ideally, this healing agent should react with the matrix or with a component added to the matrix, producing solidified products that will repair the damage. However, few methodologies allow the encapsulation of adequate healing agents and even fewer encapsulate water-based cores which play an important role on the cementitious healing. Thus, in this work we report the use of a microfluidic approach to develop microcapsules ranging between 80-90 µm with water based core and acrylate shell. After production, the capsules were integrated in the cement paste and exhibited a good survivability from the mixing process as well as good dispersion and no undesirable reaction with the matrix. Scanning electron microscopy (SEM) was used to investigate rupture of the microcapsules under cracks at 7, 14, 28 and 56 days and observations show both broken and debonded capsules. These initial results place the microfluidic approach as a promising technology for the production of the capsules and further optimization it is necessary to improve the breakage upon crack.
Session 6 : -
Authors : Alicja Stankiewicz
Affiliations : School of Engineering & the Built Environment, Edinburgh Napier University, 10 Colinton Road, Edinburgh, EH10 5DT, United Kingdom
Resume : Inspired by biological systems, artificial self-healing materials are designed for repairing local damage caused by external factors. The rapidly expanding field of self-healing systems contains among others materials with well-defined surface properties. Undoubtedly, surface functionalisation by applying smart coatings enjoys an extensive interest. The self-healing ability is particularly essential property for corrosion protection strategies, especially when the use of one of the most effective corrosion systems, based on chromium(VI) compounds, is banned by the current REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation. Self-healing protective coatings are produced using macromolecular compounds, ceramics, metals and composites. Considering the wide range of available materials, the number of potential combinations seems to be unlimited. The self-healing action of such coatings are activated by appropriate stimuli: temperature changes, radiation, pH changes, pressure changes and mechanical action. In this keynote, I will explore the research and practice implication of the various approaches to achieving self-healing functionality of protective coatings, as well as the future directions in this developing area.
Authors : Matthias Uebel, Ashokanand Vimalanandan, The-Hai Tran, Michael Rohwerder
Affiliations : Max-Planck-Institut für Eisenforschung GmbH
Resume : An important conventional way for achieving corrosion protection of metals is the application of barrier-type coating systems which contain corrosion inhibitors. AN increasingly problematic drawback of such standard coating systems is the uncontrollable leaching of inhibitor into the environment, which is leading to pollution and a shortened corrosion protection lifespan. The need to solve these problems sparked intensive research in the field of smart corrosion protection which stands for a targeted delivery of corrosion inhibitors and self-healing agents to the corrosion site only when this starts to actively corrode. Regardless of the chosen trigger for the corrosion sensitive release of the active agents, there are two critical challenges that need be solved for making such coating system really interesting for technical application: the long term performance of the coatings, i.e. whether they retain their active function also after many years of inactive exposure, and their suitability for healing also larger defects, such as scratches of one to two millimetres width. It will be shown in this presentation that there are already promising concepts to deal with the first challenge and also strategies for achieving sufficiently fast release of very high amounts of active agents for healing large defects. First results will be presented and the need for novel coating concepts will be discussed.
Authors : Jayaprakash Krishnasamy, Willem G. Sloof, Sybrand van der Zwaag, Sergio Turteltaub
Affiliations : Department of Aerospace Structures and Materials, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands; Department of Material Science and Engineering, Faculty of Mechanical, Maritime and Material Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands
Resume : Thermal Barrier Coating (TBC) systems are protective layers deposited on critical structural components operating in the high-temperature sections of gas turbine engines. These systems undergo thermo-mechanical cyclic loading leading to nucleation of micro-cracks in the coating system. Upon further cycling, these micro-cracks grow and coalesce, ultimately leading to complete failure of the thermal insulation functionality. To delay such coalescence, a self-healing mechanism is introduced into the TBC system, thereby extending its lifetime. A typical TBC system consists of three different layers, namely a ceramic top coat (TC), a thermally-grown oxide (TGO) layer and a metallic bond coat (BC). The proposed healing mechanism involves dispersing suitable healing particles in the TBC layers. Upon cracking in the TBC, the micro-cracks interact with the healing particles, which subsequently heals the cracks. For the design of an optimal self-healing TBC system, it is critical to understand its failure behavior. In particular, the locations at which cracks are likely to initiate need to be identified to judiciously distribute the healing particles. To achieve this, finite element fracture analyses employing cohesive elements are conducted. Distinct fracture properties and microstructural features such as interface roughness and porosity are considered in the simulations. The interactions between cracks and healing particles are analyzed under thermal loading. Several configurations for the healing particles have been considered in order to assess the influence of the particle distribution. This study helps to identify the optimal configuration of the healing particles for successful activation of the healing mechanism.
Poster Session II - incl. 3 min Poster Presentation : -
Authors : O. Speck, S. Anandan, C. Paul-Victor, A. Cegna, K. Schmauder, A. Rudolph, T. Speck
Affiliations : Plant Biomechanics Group and Botanic Garden, University of Freiburg, Germany; Freiburg Materials Research Center (FMF), Germany; Competence Network Biomimetics, Germany
Resume : Over the course of evolution plants and animals have evolved a variety of wound reactions. In general, a rapid self-sealing phase and a subsequent self-healing phase can be identified . In the framework of the European Marie Curie Initial Training Network Self-Healing Material: from Concepts to Market" (SHeMat) studies were carried out enabling a deeper understanding of self-repair mechanisms in plant with the aim to learn for the development of bio-inspired technical composite materials with self-repair function. Anatomical and biomechanical studies were conducted on various model plants. The selected plants were injured along the respective plant organ in longitudinal and in transversal direction and compared with undamaged control plants. During a healing time of up to four weeks a variety of anatomical features could be observed due to purely mechanical damage: (1) rolling in of the wound edges, (2) opening or closing of the wound, (3) formation of a boundary layer by the deposition of lipophilic substances (lignin, suberin, cutin) in or on the cell walls in the wound region, (4) discharge and coagulation of latex, and (5) formation of a wound periderm. Biomechanical test series showed significant change in elastic and viscoelastic properties of injured plant organs compared with undamaged control plants.  Speck T., Mülhaupt R., Speck O. (2013) Self-healing in plants as bio-inspiration for self-repairing polymers. In: W. Binder (ed.), Self-Healing Polymers, 61-89.
Authors : M. Grandcolas, N. Rival, H. Bu, S. Jahren, R. Schmid, H. Johnsen
Affiliations : SINTEF Materials and Chemistry, P.O. Box 124 Blindern, N-0314 Oslo, Norway
Resume : The concept of an autonomic self-healing material, where initiation of repair is integrated to the material, is now being considered for engineering applications (LG released in 2014 a mobile phone using a self-healing finish (LG G Flex)) and is a hot topic in the literature (SciFinder: 2090 references were found containing the concept "self-healing material"). Among several concepts/techniques, two are most interesting: i) Capsules: Integration of microcapsules in or at the surface of coatings or fibre-like structures has recently gained much attention. Upon damage-induced cracking, the microcapsules are broken by the propagating crack fronts resulting in release of an active chemical (healing agent) by capillary action, subsequently repairing and avoiding further crack growth. ii) Self-healing polymers: Interestingly, the introduction of dynamic covalent bonds into polymer networks has also recently been used as a powerful approach towards the design of various intrinsically self-healing polymer systems. The idea behind this is to reconnect the chemical crosslinks which are broken when a material fractures, restoring the integrity of the material and thereby prolonging its lifetime. We propose here to integrate both self-healing concepts (capsules, self-healing polymers) in electrospun fibres and coatings. Different capsule preparation approaches have been investigated in SINTEF. The most advanced method to produce capsules is based on emulsification to create a water-in-oil emulsion before polymerization. The healing agent is a polyurethane-based dispersion that was encapsulated in shell materials consisting of urea-benzaldehyde resins. Results showed successful preparation of microcapsules and release of the agent when capsules break. Since capsules are produced in water-in-oil systems we mainly investigated organic solvent based coatings while a major challenge resides in the incorporation of capsules into water-based coatings. We also focused on developing more robust microcapsules to prevent premature rupture of the capsules. The capsules have been characterized in terms of size, and encapsulation and release might be visualized by incorporating fluorescent dyes and examine the capsules by microscopy techniques. Alternatively, Electrospinning is an innovative technique that has attracted enormous attention due to unique properties of the produced nano-to-micro fibers, ease of fabrication and functionalization, and versatility in controlling parameters. Especially roll-to-roll electrospinning is a unique method which has been used in industry to produce nanofibers continuously. Electrospun nanofibers can usually reach a diameter down to 100 nm, depending on the polymer used, which is of interest for the concept with self-healing polymer systems. In this work we proved the feasibility of fabrication of POSS-based (POSS: polyhedral oligomeric silsesquioxanes, tradename FunzioNano) nanofibers via electrospinning. Two different formulations based on aqueous or organic solvents have shown nanofibres with diameter between 200 450nm with low defects. The addition of FunzioNano in the polymer blend also showed enhanced properties in term of wettability, promising for e.g. membrane technology. The self-healing polymer systems developed are here POSS-based materials synthesized to develop dynamic soft brushes.
Authors : Brennan M. Bailey, Yves Leterrier,S.J. Garcia, S. van der Zwaag, Véronique Michaud
Affiliations : Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; Novel Aerospace Materials group, Department of Aerospace Engineering, Delft University of Technology, 2629 HS, Delft, The Netherlands
Resume : The goal of the research to be presented is the development of electrically conductive epoxies having the ability to autonomously restore their mechanical integrity and electrical conductivity after a local fracture event. Such materials are often used in micro-electronic devices and are prone to cracking after long term usage. Our approach focuses on the use of microcapsules filled with a solvent, epoxy monomers and carbon nanotubes (CNTs) in combination with a conductive CNT epoxy composite (ECNT) containing unreacted monomers and residual hardener. Opening of microcapsules and subsequent solvent release upon crack propagation locally increases the mobility of epoxy chains and swells the matrix. This solvent-triggered reaction of the monomers with the residual hardener leads to crack closure. Herein, two different self-healing coatings and two controls based on ECNT with approximately 20% CNTs were fabricated. Electrochemical impedance spectroscopy (EIS) confirmed that coatings possessing microcapsules with an EPA:ECNT or EPA:EPON core lead to improved barrier restoration. A novel in situ electro-tensile test was developed and demonstrated that in coatings containing both microcapsules comprised of EPA and ECNT restoration of both electrical conductivity and mechanical properties to 64% (± 23) and 81% (± 39) was achieved. Most recently, a series of electro-fatigue bending tests under controlled strain amplitude were carried out using a computer-controlled apparatus equipped for electrical resistance measurements. Such testing should enhance understanding of the interplay between self-healing mechanisms and damage accumulation processes under cyclic loading, which control the fatigue endurance.
Authors : Zofia Jagoda, Alicja Stankiewicz, Katarzyna Zielińska, Irena Szczygieł
Affiliations : Department of Inorganic Chemistry, Faculty of Engineering and Economics, Wrocław University of Economics, Komandorska 118/120, 53-345 Wrocław, Poland; School of Engineering & the Built Environment, the Edinburgh Napier University, 10 Colinton Road, Edinburgh, EH10 5DT, United Kingdom; The School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, United Kingdom
Resume : The selection of construction material is often based on a compromise between desired properties and price. When the only shortcoming of such material are insufficient surface properties, the surface is secured by protective coating. It is required for modern coatings to have an ability to reproduce their original properties after damage. This is an especially important property for anticorrosion coatings. Of particular interest are coatings containing micro- or nanocapsules filled with suitably selected corrosion inhibitor e.g. cerium ions. It is desirable that the inhibitor carrier has been built with environmentally friendly materials. The new approach to the subject is use a microgels instead of a capsules. In the research we used gelatine as a carrier of active compound. The aim was to determine the conditions of preparation of microgels by the thermal gelation method in water-in-oil emulsion. The microgels were filled with brilliant blue FCF in order to facilitate of microscope observation. The influence of the process temperature, stirring rate and addition of various surfactants was examined. The best results was obtained in 80°C with the stirring rate of 1000 rpm and addition of surfactant BRIJ30 to corn oil. Prepared microgels filled with fluorescein were codeposited with Ni-P coating. The analysis of the coating with the use of the fluorescence optical microscope have confirmed the codeposition of gelatine microgels with Ni-P coating.
Authors : Liberato Ferrara, Visar Krelani
Affiliations : Department of Civil and Environmental Engineering, Politecnico di Milano Piazza Leonardo da Vinci 32, 20133 Milano, Italy
Resume : Todays huge development of concrete for civil engineering is facing the need of thinking higher. Intelligent cement based materials which sense the presence of the damage and respond with their capacity to heal the damage or, in case, recovery their pristine level of performance represent one of best response to facing this challenge. At Politecnico di Milano a comprehensive project on engineering self-healing capacity of cement based materials through the use of crystalline admixtures is ongoing for about a lustrum, whose main results are going to be summarized in this paper. Reference has been made to both a normal strength concrete and a high performance fiber reinforced cementitious composites. A methodology has been developed to assess the self-healing capacity of the investigated cementitious composites, based on either 3- or 4-point bending tests on un-cracked and pre-cracked beams, subjected to exposure to suitable environmental conditions for scheduled durations. A better and more stable recovery was shown by the concrete with crystalline additive and its interaction with fiber reinforcement is also likely to yield promising achievements, paving the way for the concept investigated in this study to be applied for engineering applications on the market. Healing indices have also been defined, to quantify the self-healing capacity as a function of the investigated variables, to reliably incorporate the effects of healing into a durability based design approach.
Authors : Sara Irico, Andrea Bovio, Geo Paul, Enrico Boccaleri, Daniela Gastaldi, Leonardo Marchese, Luigi Buzzi, Fulvio Canonico
Affiliations : Università del Piemonte Orientale A. Avogadro,Viale T. Michel 11, 15121, Alessandria, Italy; Buzzi Unicem S.p.A, Via Montesanto 5, 13039, Trino (VC), Italy
Resume : The identification of affordable healing agents for cement based materials, able to promote autonomous crack healing, is a challenge to improve the durability of building structures. In this study, a deep investigation of the reactivity and of the final properties of hydrated Portland cement powders with sodium silicate solutions, as healing agents, have been carried out. The goal is to quantitatively assess the chemical reactivity and actual binding capacity of sodium silicate. Mechanical recovery was evaluated with a healing agent compressive strength test on powdered cement, where mixing of sodium silicate gave a compressive strength up to 10.9 MPa. XRPD and Solid-state NMR allowed to define reaction times, the involved species, the nature and the stability of the reaction products. Highlights show that sodium silicate reacts not only with portlandite, but also with aluminate phases (AFt, AFm, TAH) to extract calcium and/or aluminum ions, with the formation of crystalline/semi-crystalline C-S-H/C-A-S-H tobermorite phase.
Authors : Maria Araújo, Sandra Van Vlierberghe, Peter Dubruel, Nele De Belie
Affiliations : Polymer Chemistry and Biomaterials Group (Department of Organic and Macromolecular Chemistry) and Magnel Laboratory for Concrete Research (Department of Structural Engineering); UGent, Belgium
Resume : Cracking in concrete is frequently a concern since these cracks can provide easy entry channels for the penetration of aggressive liquids and gases into the concrete, leading to deterioration. The repair of these cracks is, therefore, indispensable. However, manual crack repair is expensive and difficult when cracks are not visible or accessible. Thus, the design of concrete with self-healing properties would be highly beneficial to improve its durability. One of the crack repair approaches makes use of capsules sequestering polymer-based healing agents. The self-healing mechanism is triggered upon crack formation, leading to release and reaction of the healing agent in the zone of damage. In the present work, we aimed at determining the most suitable polymer backbone to be applied for self-healing of cementitious materials. For this purpose, several key prerequisites such as viscosity, curing time and mechanical properties of different polymeric precursors including siloxane-, urethane-, epoxy- and polyester-based have been evaluated. To assess the effect of high alkalinity on the degradation of the polymerized healing agents, stability tests have been performed. The results indicate that different healing agent solutions show adequate curing time, viscosity and mechanical properties. The various healing agent solutions were manually injected into cracks of mortar samples to evaluate their sealing capability and strain capacity.
Authors : Tanvir Qureshi and Abir Al-Tabbaa
Affiliations : Department of Engineering, University of Cambridge, Trumpington Road, Cambridge CB2 1PZ, United Kingdom
Resume : Excessive drying shrinkage in the concrete is one of the major concerning issues for longevity and reduced strength performances in the structure. It can causes formation of cracks in the concrete. This research aimed to improve the autogenous self-healing capacity of traditional Portland cement (PC) systems adding reactive magnesium oxide (MgO) in terms of drying shrinkage crack healing. Two different reactive grades (high N50and moderately high 92-200) of MgO were added with PC. Cracks were induced in the samples with restraining end prisms due to natural drying shrinkage over 28 days after casting. Samples were than cured under water for 28 days and self-healing capacity was investigated in terms of mechanical strength recovery and crack sealing efficiency. Finally, microstructures of the healing materials were investigated using FT-IR, XRD, and SEM-EDX. Overall N50 mixes shows higher expansion and drying shrinkage compared to 92-200 mixes. Mechanical strength regain of the MgO containing samples were much higher compared to control (only PC) mixes. Cracks up to 500 µm were sealed in most MgO containing samples after 28 days. In the microstructural investigations, highly expansive hydromagnesite bridges were found along side with traditional calcium based self-healing materials (calcite, portlandite, calcium silicate hydrates and ettringite).
Authors : Eleni Tsangouri;Grigorios Karaiskos;Pieter Minnebo;Dimitrios Aggelis;Danny Van Hemelrijck
Affiliations : Department of Mechanics of Materials and Constructions (MeMC), Free University of Brussels (VUB) & SIM program, Belgium
Resume : The research done from the idea catching to the market release consists of two main tasks: 1. design of material with self-healing ability; 2. test to evaluate the materials' innovative performance. Regarding the building materials, such as concrete and polymer composites, the evaluation mostly considers the mechanical resistance to damage after healing. The research done the previous 4 years at the Department of Mechanics of Materials and Constructions (MeMC-VUB) and with the financial support of SIM program regards the experimental assessment of healing efficiency. Both polymer composites (self-healing microencapsulation approach) and concrete (self-healing hollow-tube encapsulation approach) elements are tested and their mechanical response is extensively investigated by combining several advanced experimental techniques. It is shown that the quantification of the healing efficiency is not a straight-forward measurement and requires the combination of fracture mechanics theories (modelling the crack phenomena and measurement of the resistance of the self-healed material to damage), optical (visualization and continuous inspection of crack evolution) and acoustic (detection of healing activation and assessment of toughness built after repair) techniques.
Authors : P.T.M. Albers, L.G.J. van der Ven, R.A.T.M. van Benthem, A.C.C. Esteves, G. de With
Affiliations : Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; Laboratory of Materials and Interface Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; Dutch Polymer Institute (DPI), Eindhoven, the Netherlands; DSM Ahead BV Netherlands, Geleen, The Netherlands
Resume : The lubricous character of hydrophilic coatings is particularly important for bio-medical devices which are in contact with the human body in order to increase the patients comfort and reduce the risk of device-associated infections. The potential reduction of hydrophilic groups at the surface, by hydrolysis or wear, lowers the lubricating performance. In order to maintain high performance during an increased service lifetime of the coated device, an autonomous replenishing mechanism for restoring the lubricious surface functionality would be desired. Implementing a self-replenishing mechanism into a hydrophilic lubricious coating requires a profound knowledge of the actual friction behavior of hydrophilic networks. Although used since long, the aqueous friction mechanics of hydrophilic networks are very complex and still poorly understood. In order to increase insight in the structure-property relations of hydrophilic coatings and to tune their lubricity properties, a study of the relation between the network parameters, the mechanical properties and resulting wet friction behavior of well-defined hydrophilic networks is needed. We report our progress on the study of the influence of the network parameters on the network and wet friction properties of well-defined PEG-based hydrophilic PU networks. In a following step, this knowledge will be used to introduce a self-replenishing mechanism into the hydrophilic networks aiming for the recovery of the lubricious character.
Authors : I. Jiménez-Pardo, P. P. W. Mommers, L.G.J. van der Ven, R.A.T.M. van Benthem, A.C.C. Esteves, G. de With
Affiliations : Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; Laboratory of Materials and Interface Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; DSM Ahead BV Netherlands, Geleen, The Netherlands
Resume : Functional marine coatings are permanently in contact with water and inevitably accumulate organisms on their surface, i.e. bio-fouling, which increases drag reduction and fuel consumption. Furthermore, they are constantly subjected to damage by the maneuvering and transport operations, requiring maintenance and dry-dock repair. Several anti-fouling (AF) strategies have been reported for marine coatings. However, once the surface characteristics are lost, upon damage or attachment of the first organisms, the AF properties are no longer effective and the ships, boats or platforms will become fouled rapidly. Introducing a self-repairing mechanism, which can intrinsically replenish the damaged surface with new AF chemical moieties, will allow a high performance level throughout the life-time of the coatings, with major economic and environmental benefits. Our current studies focuses on developing hydrophilic self-replenishing coatings, targeting application areas such as marine AF coatings. To this purpose, we designed systems with polyurethane-based networks containing PEG moieties, i.e. dangling chains, which preferentially orient towards the water-coating interfaces, providing AF properties. Preparation of the AF hydrophilic networks and their characterization by CA, AFM and QCM measurements will be presented. In future work, systems will be tuned to have self-healing characteristics, recovering the surface functionalities, such as hydrophilicity and AF behavior.
Authors : E. Iype, L.G.J. van der Ven, R.A.T.M. van Benthem, A. C. C. Esteves, G. de With
Affiliations : Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; Laboratory of Materials and Interface Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands; DSM Ahead BV Netherlands, Geleen, The Netherlands
Resume : Anti-fouling hydrophilic polymer coatings are of high interest for marine and biomedical applications. However, these coatings will rapidly lose their performance, if the surface characteristics are lost. Introducing a self-replenishing mechanism into hydrophilic coatings, will improve performance and life-time of the coated surfaces. Polyurethane (PU) cross-linked networks are good candidates for self-replenishing hydrophilic polymer coatings. PU networks have been reported to exhibit characteristic phase separation between hard and soft segments. Understanding this phase-separation behavior, is imperative to design efficient self-healing polymer coatings. Most of the studies on the morphology of cross-linked networks are experimental only. We present a Dissipative Particle Dynamics simulation study of the behavior and network characteristics of model hydrophilic polymer networks, consisting of PU with and without mPEG dangling chains. We analyzed the systems using a number of tools such as, radial distribution function, cross-link distribution, Voronoi volume, etc. While the network without dangling chains is homogeneous, a clear phase separation is observed when introducing dangling chains. In spite of the significant phase separation, the amount of cross-linker molecules connected only to dangling chains, i.e, not connected to the main network, is negligibly small. Thus, the morphology of these cross-linked polymers shows a stable network, yet phase separated.
Authors : Rajeswari Narayanasamy, Gerardo del Jesús Fajardo San Miguel, Héctor Herrera Hernández, Nagamani Balagurusamy
Affiliations : Facultad de Ingeniería, Ciencias y Arquitectura de la Universidad Juárez del Estado de Durango; Facultad de Ingeniería Civil de la Universidad Autonoma de Nuevo Leon; Centro Universitario, Universidad Autonoma del Estado de Mexico; Facultad de Ciencias Biologicas, Universidad Autonoma de Coahuila, Mexico
Resume : In this study, the novel technique of microbial induced precipitation of carbonate (MICP) to improve the physical properties of sand, concrete and stone was employed. Soil bacteria isolated from the region of the Laguna Region, North east Mexico and shown the ability to form calcite by means of urease activity were selected. Two bacterial strains, ACRN 3 and ACRN 5 were added at different concentrations to the mixture of cement and sand at a ratio of 1: 2.75 to study their effect on the maximum resistance of mortar cubes in comparison with conventional mortar cubes (control). This results demonstrated a significant increase in compressive strength of mortar cubes at a bacterial concentration of 105 per millitres. Between the bacterial strains tested, ACRN 5 perfomed better than ACRN 3. Studies on electrical resistivity and quick permeability tests of the mortar cubes showed that bacterial addition improved their characteristics. XRD, ESEM, XRF and EIS analyses of the biomortars are under progress. Key words: bacteria, biomortar, compressive strength, resistivity, permeability
Authors : Liam Carter
Affiliations : University of Cambridge, Department of Engineering, United Kingdom
Resume : A microcapsule based self-healing method for cementitious materials was investigated as a feasibility study, using microfluidically produced polymer shell microcapsules. Double emulsions formed using a commercially available microfluidic chip were used to produce liquid core microcapsules by UV polymerisation of the acrylate monomer shell. The effect of fluid volumetric flow rate on the capsule dimensions was investigated. Capsules were cast in small cement paste prisms to view their behaviour in a fracture plane. Upon fracture of freshly de-moulded samples, capsules were seen to pull out of the matrix rather than fracture, indicating poor bond strength with the cement matrix. Continued hydration of samples for 3 days gave improved results, the liquid core of the capsules was observed to have flown from damaged capsules using scanning electron microscopy. However, capsule fracture only appeared to occur due to crushing under compressive load and bonding was still not sufficiently strong to inhibit pull out in tensile loading. Should a healing agent be encapsulated within the shell, the fracture may facilitate self-healing behaviour. In conclusion, although further work is required to increase the capsule-cement bond strength, there is promise for the use of microfluidics in self healing cementitious materials.
Authors : Elke Gruyaert, Ghislain Louis, Damien Betrancourt, Yusuf Ersan Cagatay, Christine Lors, Denis Damidot, Nele De Belie
Affiliations : Magnel Laboratory For Concrete Research, Technologiepark Zwijnaarde 904, 9052 Ghent, Belgium; Ecole des Mines de Douai, Boulevard Lahure 741, 59500 Douai, France
Resume : CaCO3 precipitation is one of the main mechanisms to heal cracks in bacterial based self-healing concrete or self-healing concrete incorporating superabsorbent polymers (SAPs), but also in traditional concrete, cracks can be healed autogenously due to CaCO3 precipitation. To study the mechanical properties of the CaCO3 precipitated in the cracks of these three types of concrete, the indentation technique was used. A scanning electron microscope (SEM) equipped with a special stage to combine the indentation technique with SEM/EDS (energy dispersive X-ray spectroscopy), was used in this study. The advantage of this system is that the location of the indentation test can be accurately determined and it is known for certain for which phase the mechanical properties are measured and calculated. The results show that there is no significant difference in the Martens hardness of the calcite formed in autogenously healed specimens and specimens incorporating bacteria or SAPs. Furthermore, the mechanical properties of the cement paste were also measured and the influence of the strength class of the cement (CEM I 42.5 N vs. CEM I 52.5 N) and presence of SAPs was investigated. This work was supported by the SHeMat project "Training Network for Self-Healing Materials: from Concepts to Market" within the scope of the Seventh Framework Programme [FP7/2007-2013] under grant agreement no 290308 by the European Commission's Marie Curie programme.
Authors : Ali Behnood, Christian Simon, Emmanuel Cailleux, Yegor Morozov, Fatima Montemor, Sviatlana. Lamaka, Kim Van Tittelboom, Nele De Belie
Affiliations : Magnel Laboratory for Concrete Research, Department of Structural Engineering, Faculty of Engineering and Architecture, Ghent University, Technologiepark Zwijnaarde 904, B-9052 Ghent, Belgium; SINTEF Materials and Chemistry, Forskningsveien 1, 0314, Oslo, Norway; Belgian Building Research Institute, Avenue Pierre Holoffe 21, B-1342, Limelette, Belgium; Centro de Quimica Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Portugal 5Magnesium Innovation Centre, Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Germany
Resume : Recently, self-healing concrete has been introduced as a novel construction material which can result in a considerable reduction in annual maintenance costs of concrete structures such as bridges, tunnels and retaining walls. Although many research works have been done for optimizing properties of self-healing concrete, the bottleneck for its valorisation is the encapsulation method of the healing agent because the capsules have to demonstrate multifunctional properties. They (i) have to protect the healing agent over long time, (ii) have to release the healing agent upon crack formation and (iii) should not affect the fresh concrete workability and the early and long term mechanical properties. Moreover, it is essential that capsules can easily be mixed in concrete and/or can survive during concrete casting. Consequently, the concrete production process is not remarkably affected and the processing costs will almost not increase. In addition, the capsules should provide good barriers against both oxygen and water to protect the healing agent. These requirements may cause difficulties in finding a suitable encapsulation material because the capsules should not be broken during concrete preparation whereas they should break immediately upon crack formation. Although no commercial product seems suitable for these purposes, within the CAPDESIGN project it is aimed to develop, optimize and test novel types of capsules for application in self-healing concrete. Hybrid nanoparticles developed at SINTEF will be used to improve both mechanical properties and barrier properties of the capsules. Within this project, it is also the aim to develop capsules which can be applied to the concrete via an innovative placement technique. The advantage of capsules which survive during mixing/operation are (i) decreasing the cost of self-healing concrete, (ii) facilitating production of self-healing concrete by companies, (iii) open the possibility to valorise self-healing concrete. Consequently, mass production of self-healing concrete structures which do not require maintenance costs will result into a lot of economic, environmental and social advantages such as less traffic jams or higher safety levels.
Authors : J. Feiteira, E. Gruyaert, N. De Belie
Affiliations : Magnel Laboratory for Concrete Research, Ghent University, Technologiepark-Zwijnaarde 904, 9052 Ghent, Belgium
Resume : Self-healing concrete aims at the autonomous healing of small cracks, with widths in the order of a few hundred micrometers. This way, the service life of reinforced concrete structures can be extended and their watertightness guaranteed for longer periods, while costly and potentially complex repair works can be avoided. As with other emerging concrete technologies, this novel repair technique poses new challenges regarding the conception of new test methods that are able to assess its performance in realistic conditions and able to continuously monitor it. Thus, this paper presents results of applying the transmission of ultrasonic shear waves for continuous monitoring of small scale cement mortar specimens cracked and healed with encapsulated precursors of flexible polymers. Preliminary results on larger concrete specimens showed already that this technique successfully detects the continuous hardening of the precursors after rupture of the capsules and further filling of the crack, corresponding to an increase of the amplitude of shear waves transmitted through the healed crack. Additionally, the reverse was observed when failure occurred, due to rupture of the polymers matrix or to its detachment from the crack walls. In this study, the transmission of ultrasonic shear waves is used to assess the limits of the elongation of the polymers bridging the cracks and their resistance to fatigue while healing a moving crack induced by cyclic loads. The polymer precursors used include moisture curing polyurethanes forming solid films or foams with closed-cell structure. ACKNOWLEDGEMENTS The research has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 309451 (HEALCON).
Authors : Rami Alghamri, Abir Al-Tabbaa
Affiliations : Department of Engineering, University of Cambridge, Cambridge, United Kingdom
Resume : Utilization of expansive agents and mineral admixtures as an approach for self-healing of cementitious composites has been the subject of extensive research over the last two decades. However, it has been consistently shown that the main challenges of this approach are the significant loss in workability of fresh concrete and the occurrence of early reactions with cementitious materials, which would decrease the self-healing efficiency. Therefore, this work aims to study the influence of incorporating coated pellets with different cargoes of expansive minerals into the cementitious composites on the crack self-healing performance with the elapse of time. Four different types of pellets containing (1) Blend of high reactive Magnesium Oxide (MgO) and Bentonite, (2) Blend of MgO and Silica fume, (3) Low reactive MgO and (4) Medium reactive MgO were used. The first two types were developed in the laboratory while the latter two are commercial pellets. All of them are with (1-2) mm diameter and they were coated by a film layer of polyvinyl alcohol (PVA) to control the time of autonomic healing. These coated pellets were added to mortar mixes as partial sand replacement. Controlled width cracks of 300 µm were induced in three prism specimens from each mix after 7 days of curing in water. Then monitoring of cracks closure using optical microscope images was applied every 7 days for 28 days. Thereafter, the specimens were re-cracked by three point bending test to examine their flexural strength recovery. The results indicate that the mortar samples containing the coated pellets possessed promising crack self-healing performance compared to the control samples with superiority to those developed in laboratory.
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Session 7 : -
Authors : J. M. García-Aznar, M. J. Gómez-Benito, E. Javierre
Affiliations : University of Zaragoza, Aragón Institute of Engineering Research, Dept. of Mechanical Engineering, Campus Rio Ebro, 50018 Zaragoza, Spain
Resume : Both soft and hard tissues are able to adapt their mechanical properties in response to the mechanical demands that they are supporting, even they are able to regenerate or heal when a fracture or injury occurs. The main actuators that regulate this adaptive and regenerative behaviour are the cells. These are able to sense the mechanical alterations and regulate their activity in order to remove dead tissue and/or create new tissue. Therefore, understanding how cells are able to regenerate tissues under complex and multiphysics conditions can define the biomimetics guidelines to heal inert or traditional engineering materials. In this work, we present a combination of experiments and different kind of multiscale and multiphysics models in order to understand how mechanics is regulating some mechanisms at cell and tissue level. This combination of results aims to get insight in the development of novel strategies for self-healing materials, mimicking the behaviour induced by cells and biological tissues.
Authors : S.Anandan, T.Speck, O.Speck
Affiliations : Plant Biomechanics Group and Botanic Garden, University of Freiburg, Germany; Freiburg Materials Research Center (FMF), Germany; Competence Network Biomimetics, Germany
Resume : During evolution succulent plants have evolved the ability to store water and to rapidly seal wounds and subsequently heal injuries as an adaptation to survive in dry arid environments . The current study about self-repair in succulent plants is part of the European Marie Curie Initial Training Network for Self-Healing Materials - from Concepts to Market (SHeMat). The results will provide fundamental knowledge on self-repair in plants and to biomimetic innovations for constructing innovative technical self-healing materials. After a screening three species Sansevieria cylindrica, Rhipsalis baccifera ssp. mauritiana and Euphorbia tirucalli were selected based on their outstanding self-sealing and self-healing performance along with uniform rod shaped succulent stems or leaves. After artificial damages in cross-sectional and longitudinal direction of the plant organs, anatomical changes were carefully analysed. Thin sections of the wound region were stained with the overview staining Fuchsin Chrysoidine Astra Blue (FCA) and a special staining for lignified tissues (Acridine Orange). The plants were observed for a period of 21 days, on a daily basis for the first 3 days and later each second or third day, to have an impression of structural changes occurring during the self-repair processes in the plants.  Speck T., Mülhaupt R., Speck O. (2013) Self-healing in plants as bio-inspiration for self-repairing polymers. In: W. Binder (ed.), Self-Healing Polymers, 61-89.
Authors : T. Speck, G. Bauer, R. Mülhaupt
Affiliations : Plant Biomechanics Group and Botanic Garden, University of Freiburg, Germany; Freiburg Materials Research Center (FMF), Germany; Freiburg Centre for Interactive Materials and Bioinspired Technologies (FIT), Germany; Institue for Macromolecular Chemistry, University of Freiburg, Germany
Resume : Self-sealing and self-healing are common in living beings and occur on all hierarchical levels from macromolecules to entire organisms. In manmade materials, on the other hand, self-repair remains largely unexplored. Based on the self-repairing processes found in latex bearing plants, bio-inspired solutions are being developed in interdisciplinary R&D-projects. One type of these biomimetic materials are self-repairing elastomers for mechanically highly loaded sealing gaskets and dampers inspired by the self-repairing processes found in latex plants such as weeping fig, rubber tree and various spurges which very efficiently seal fissures by latex coagulation [1,2]. In the most promising approach bio-inspired multiphase blends of nitrile butadiene rubber (NBR) with liquid polymers (hyperbranched polyethyleneimine, PEI) as self-repairing agent were developed. This represents an alternative to micro-encapsulation of self-reparing agents avoiding the micro-capsule by phase separation, and the liquid polymer is under a high internal pressure in the micro-phase separated domains. For vulcanized NBR/PEI blends the self-healing efficiency amounts to 44% (measured as %-recovery of tensile strength of strips cut in half and then rejoined) .  Bauer G., Gorb S., Klein M.C., Nellesen A., v. Tapavicza M., Speck T. (2014) PLoS ONE 9. e113336. DOI: 10.1371/journal.pone.0113336.  Bauer G., Friedrich C., Gillig C., Vollrath F., Speck T., Holland C. (2014) Journal of The Royal Society Interface, 11. DOI.org/10.1098/rsif.2013.0847.  Speck T., Mülhaupt R., Speck O. (2013) Self-healing in plants as bio-inspiration for self-repairing polymers. In: W. Binder (ed.), Self-Healing Polymers, 61-89.
Session 8 : -
Authors : D. H. Turkenburg, H. R. Fischer, T. S. Coope, R. Luterbacher, I. P. Bond
Affiliations : TNO Science and Industry,The Netherlands; University of Bristol, United Kingdom
Resume : For aerospace composites, the possibility of self-healing functionality would be of high added value. Thermoset epoxy amine systems are commonly used because of their excellent mechanical properties, compatibility with carbon fibers and chemical inertness. Once the composites are cured however there is not much that can be done about defects (micro-cracks and fiber-resin delamination). We developed a process that allows to combine Diels-Alder functional components with a conventional epoxy amine system. The obtained material displays an interesting mixture of properties some of which are typical for classical thermoset polymers, others for thermoplastics. The thermo-reversible nature of the Diels-Alder reaction allows the material to flow and self-repair at temperatures >120°C as is characterized using rheological studies. Self-healing of test specimens has been demonstrated. In analogy to epoxies, due to its rigidity, mechanics and thermoset behavior (high crosslink density proven by solvent resistance) the developed material could be used to construct fiber reinforced polymer composites. The synthetic route does not require complex equipment or process conditions and the starting materials are cost efficient (no catalyst is needed), large scale available and commonly used by the aerospace industry. Multiple temperature triggered self-healing event have been established with high healing efficiency. This work was funded by the EU http://www.hipocrates-project.eu/
Authors : Federica Sordo, Véronique Michaud
Affiliations : Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
Resume : We propose a novel approach to develop self-healing composites by using an intrinsic self-healing polymer as the matrix, and high volume fraction fabrics as the reinforcement. Reverlink® HR-NR (from Arkema), a commercially available partially supramolecular, partially cross-linked elastomeric material, was selected as the matrix. Its self-healing ability derives from the presence of reversible hydrogen bonds within a disordered network, that are able to reform, once broken, with an efficiency of about 65% for the tension energy at break, after 24 hours at room temperature. High quality glass fibers reinforced composites, characterized by a fiber volume fraction of 50% and a porosity of max 4%, were produced using an adapted vacuum assisted resin infusion molding process (VARIM) into stacks of woven twill 2x2 E-glass fabric (Suter-Kunststoffe AG) with a nominal areal weight of 390 g/m2. The thermo-mechanical properties of the composites were quantified by tensile test and dynamic mechanical analysis (DMA). The composites were relatively stiff in the fiber direction, with an average ultimate strength of 1.37GPa, maintaining high damping properties in the direction orthogonal to the weave. Their self-healing ability was evaluated with 3-point bending and impact tests. A high recovery of the flexural properties, around 94% for the elastic modulus and 54% in yield strength was achieved after a resting period of 24 hours at room temperature. Recovery after impact was also observed.
Authors : A. Kotrotsos, A. Baltopoulos, S. Tsantzalis, X. Tsilimigkra, P. Tsokanas, D. H. Turkenburg, H. R. Fischer, V. Kostopoulos
Affiliations : Applied Mechanics Lab., Department of Mechanical Engineering and Aeronautics, University of Patras. Patras University Campus, GR 265 00 Patras, Greece
Resume : The extension of the working life and safety of the fiber reinforced plastics (FRPs), are lately under investigation. In that sense, the development of a new class of cross-linked polymers capable of healing internal cracks and delaminations through thermo-reversible bonds is currently proposed. In the present investigation, bis-maleimide (BMI) prepolymer powder with particle size of 100μm was successfully incorporated in the mid-plane of CFRPs. Reference and samples with 60, 120 and 240 grams per square meter (gsm) were produced and tested under mode I and mode II remote loading conditions. All the samples contain 22 layers of UD carbon pre-preg, while the manufacturing root was that of autoclave. The incorporation of the BMI-prepolymer powder was predefined along the crack propagation region, according to AITM 1.0005 and 1.0006 standards. After the manufacturing process all the samples were tested under mode I and II fracture tests and the results were compared against the reference one. The modified with BMI powder composites showed a slight increase for the interlaminar fracture energy both in mode I and II (GIC & GIIC). After the crack propagation up to a certain length, the samples were heated and fractured again several times in order to calculate the healing efficiency. It was shown the higher the BMI gsms, the higher the healing efficiency value under mode I experiments while all the mode II samples showed high healing efficiency values.
Authors : T. S. Coope, R. Luterbacher, D. H. Turkenburg, H. R. Fischer, I. P. Bond
Affiliations : Advanced Composites Centre for Innovation and Science (ACCIS), University of Bristol; TNO Materials, The Netherlands
Resume : Internal microscopic damage is ubiquitous in composites that have been subjected to damage, whether this be during the manufacturing process (i.e. via thermal stresses), from machining (i.e. drilling holes), during component assembly or ultimately from in-service loading. In this research, specific industry relevant fibre reinforced polymer (FRP) composite component features have been investigated and re-engineered to incorporate an in-situ repair mechanism. Functionally reactive agents (i.e. self-healing agents) were embedded into carbon and glass FRP prepreg-based laminates and tested in double cantilever beam (DCB), open-hole tension (OHT) and skin-stiffener debond specimens; to represent specific areas or design features of high stress concentration where damage predominately occurs during manufacture and in-service. The embedded self-healing agents are thermally activated post-damage to repair the internal structure. Specific self-healing chemistries (i.e. via epoxy-amine polymers containing Diels-Alder based thermo-reversible bonds and/or epoxy resin healing agents) have been utilised to achieve multiple healing cycles in order to address and manage damage generated throughout a composite components life cycle. From an initial proof of concept study, results have shown that a material recovery value of greater than 50% fracture strength has been achieved in a high performance prepreg-based FRP composite material using conventional composite manufacturing techniques.
Session 9 : -
Authors : Jasper Michels, Jolt Oostra, Paul Blom
Affiliations : Max Planck Institute for Polymer Research, Mainz, Germany; Zernike Institute for Advanced Materials,University of Groningen, Groningen, The Netherlands
Resume : Production of large area organic light-emitting diodes (OLEDs) and solar cells (OSCs) suffers from a high scrap cost due to the occurrence of defects leading to device short circuiting. These defects relate to imperfections in the organic thin film stack and are a consequence of particle contamination or incomplete coverage. The fact that these flaws are already present prior to cathode deposition makes post-production repair procedures cumbersome. Innovative strategies are desired that annihilate the detrimental consequences of such flaws during device production itself. This contribution proposes a highly effective repair procedure based on the interruption of the electronic conductivity of the organic anode by means of local over-oxidation by aqueous hypochlorite. Transient conductivity loss is understood in terms of a percolation model integrated with an effective oxidation rate law. The model allows for the definition of a suitable processing window in terms of oxidizer concentration and treatment time. Treatment of defected OLEDs and OSCs gives complete recovery of device performance, both optically and electronically. In the case of OSCs a more general alternative strategy is discussed by means of equivalent circuit modeling. Validated by current-voltage measurements these calculations define cathode design rules that maximize robustness against current leakage without sacrificing performance efficiency.
Authors : S. Zhang, E. Brück, S. van der Zwaag, N.H. van Dijk
Affiliations : Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft, The Netherlands; Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
Resume : When exposed to moderate stress levels at elevated temperatures for long times steel components can exhibit creep fracture, which arises from the formation, growth and coalescence of (initially) nanoscale pores at the grain boundaries. Self healing of such pores is a promising new approach to enhance the component lifetime. We demonstrate that self healing is achieved by precipitation of substitutionally dissolved Au and Mo atoms in the iron lattice on the creep cavity surface slowing down or even stopping further growth. The creep behaviour and microstructure evolution is studied for Fe-Au and Fe-Mo model alloys for different applied stress levels at a constant temperature of 550 oC. We found that an efficient self healing of creep damage can be achieved in the Fe Au alloy by selective precipitation of solute Au at the creep cavity surface . The self healing of creep damage by site-selective Au precipitation results in and improved creep life time. A similar site-selective precipitation at creep defects was also observed for solute Mo in the Fe Mo alloy. The mechanism for the improved creep lifetime is clarified further by microstructural studies of the Fe-Au and Fe Mo alloys after creep failure using Electron Microscopy (SEM, TEM, EBSD, EBSD) and Atom Probe Tomography (APT). For lower stress levels pore filling fractions of up to 80% have been observed.  S. Zhang, C. Kwakernaak, W.G. Sloof, E. Brück, S. van der Zwaag, N.H. van Dijk, Adv. Eng. Mater. 17 (2015) 598.
Session 10 : -
Authors : Antonio Feula, Xuegang Tang, Ioannis Giannakopoulos, Ann M. Chippindale, Clive R. Siviour, C. Paul Buckley, Ian W. Hamley, Wayne Hayesa
Affiliations : Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, United Kingdom; Department of Engineering Science, Oxford University, Parks Road, Oxford, OX1 3PJ, United Kingdom
Resume : In this paper, we report the synthesis and healing ability of a supramolecular polyurethane network whose mechanical properties can be recovered efficiently (> 99%) at the temperature of the human body (37 ?C). Rheological analysis revealed an acceleration in the drop of the storage modulus above 35 ?C, on account of the dissociation of the supramolecular polyurethane network, and this decrease in viscous nature enables the efficient recovery of the mechanical properties. Microscopic and mechanical characterisation has shown that this material is able to recover mechanical properties across a damage site with minimal contact required between the interface than previously reported systems, and also demonstrated that the mechanical properties improved when compared to other low temperature healing elastomers or gel-like materials. This supramolecular network material also exhibited excellent adhesion to pig skin and could be healed completely in situ post damage indicating that biomedical applications could be targeted, such as artificial skin or wound dressings with supramolecular materials of this type.
Authors : M. von Tapavicza, A. M. Schmidt, A.Nellesen
Affiliations : Fraunhofer Institute for Environmental, Safety, and Energy Technology, UMSICHT, Osterfelder Str. 3, 46047 Oberhausen, Germany; University of Cologne, Faculty of Mathematics and Natural Science, Department of Physical Chemistry, Luxemburger Str. 116, 50939 Cologne, Germany
Resume : Towards the past years, the development of elastomers that possess a self-healing capability gathered more and more attention in scientific research. Different chemical and physical principals were applied to trigger the restoration of mechanical properties and different characterization methods were applied to prove the concept. Some of those presented conceptions and the resulting materials are foreseen to reach market maturity and considerable technical influence. As maximum stress and strain at break are usually some of the most crucial parameters to describe properties and determine applications of a compound, tensile testing using macroscopically ruptured and standard specimen is applied to quantify the healing effectiveness. Those quantification methods are mostly inaccurate and results may differ widely due to small contact areas while reassembling cut through samples and flexibility and deformability of the material. In this research, an advanced technique to mechanically quantify the abilities is presented. Non-standard cylindrical testing specimens are prepared of different low-filled NBR based compounds featuring self-healing capacities. The samples are macroscopically damaged, healed and tensile tested. Due to enhanced cross-sectional areas, this method allows a more precise and reproducible quantification of the desired healing values, in this particular case the tensile strength. Furthermore, the geometrical shape leads to a uniform deformation of the healed surface achieving regular distribution of stress.
Authors : A. M. Grande, S. J. Garcia, S. van der Zwaag
Affiliations : Novel Aerospace Materials, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, The Netherlands
Resume : Nowadays several approaches have been developed to add healing functionality in elastomers adopting different reversible chemistries (e.g. hydrogen bonding, disulphide bridge or ionomers) and different healable polymeric materials have been recently presented in literature. A thorough understanding of the healing phenomena is then required for the further development and application of such materials. However there is no generally accepted method for evaluation of healing efficiency and most researchers have used the recovery of tensile strength of broken samples as the measure of the healing preventing a comprehensive comparison of the true healing potential exhibited by these novel materials. In this research, a fracture mechanics testing procedure, based on the evaluation of the J-integral parameter, is proposed to investigate the healing behaviour of healable elastomers. Various materials based on different reversible chemistries are tested under tensile and fracture experimental conditions. The obtained results demonstrate how the fracture protocol is more suitable to identify the relevant physical and chemical processes across the interface between two former fracture surfaces providing more quantitative information on the healing behaviour respect to the tensile testing procedure. Furthermore a first comparison of the healing performance is presented highlighting the pros and cons of the different healable elastomeric systems.
Authors : Javier Lopez, Robert Blo?e, Eckhard Weidner
Affiliations : 1) GKT Gummi und Kunststofftechnik Fürstenwalde, Tränkeweg 3 15517 Fürstenwalde, Germany; 2) RUB Bochum University, Universitätsstr. 150 44801 Bochum, Germany; 3) Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT, Osterfelder Str.3 46047 Oberhausen, Germany
Resume : Isobutylene Isoprene Rubber (IIR) is a material used for producing tire mousse for motocross competition. By normal using its mechanical properties decrease dramatically. Temperature and pressure on tires, both caused by friction, provoke the appearance of cracks and several important structure failures. The objective of this research is the production and evaluation of a polymer based on IIR which is capable to recover autonomously its mechanical properties using heat as thermal activation. For this purpose, cracks should be closed using a functional additive. It is based on an ionomeric cluster mechanism which it heals cracks on IIR. It can prevent and reduce creation and propagation of cracks that limit or collapse the original functionality of the material. The temperature of normal use of the material is used in the ionomeric mechanism to lead to an autonomic self-healing triggering a reorientation of the bonds structure closing partially the formed cracks. In this research, it is formed a mixed polymeric system based on a previous defined composition for IIR with different grades of a selected carboxyl functional ionomer (SURLYN) in weight composition and also vulcanized to low pressures and temperatures in order to get a mousse structure. A razor blade was used for conducting an artificial crack in the material. Several temperature conditions have been tested to trigger self-healing behaviour. Samples were treated at different temperatures and time steps. Tensile strength tests have been carried out as self-healing quantification method by registering tensile strength at break and strain. After a reproducible crack and healing treatment with temperature, an improvement of recovery of mechanical properties was observed for among grades of IIR-ionomer system respect to reference material recovery of IIR values. This work was supported by the SHeMat project "Training Network for Self-Healing Materials: from Concepts to Market" within the scope of the Seventh Framework Programme [FP7/2007-2013] under grant agreement no 290308 by the European Commission's Marie Curie programme.
|18:00||Best Student Presentation Awards Ceremony and Reception (Main Hall)|
No abstract for this day
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