Cellulose electronics and photonics: a new challenge for materials a new opportunity for devices

Resume : Cellulose nanocrystals (CNCs) are lyotropic colloidal liquid crystals (LCs). They can easily be obtained from wood and other biomass, and typically have dimensions of 5-10 nm × 100-500 nm. When prepared with sulfuric acid, the CNCs are modified with sulfate half-ester groups that impart a surface charge and enable them to form stable colloidal suspensions in water. Owing to the large aspect ratio and inherent chirality of the CNCs, they can spontaneously form left-handed chiral nematic LC structures at low concentrations (~4 wt.%). Chiral nematic liquid crystals (CNLCs), also known as cholesteric LCs, are important for displays and other applications owing to their periodic helical structures. Responsive photonic crystals have potential applications in mechanical sensors and soft displays; however, new materials are constantly desired to provide new innovations and improve on existing technologies. To address this, we have developed a suite of scientific solutions based on the actuating and piezoelectric responses of CNCs and stretchable CNC-polymer nanocomposite systems. For instance, stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites can be prepared to exhibit reversible visible colour upon the application of mechanical stress. When stretched (or compressed) the colourless materials maintain their chiral nematic structure but the helical pitch is reduced into the visible region, resulting in coloration of the CNC-elastomer composite. By increasing the percentage elongation of the material (ca. 50–300%), the structural colour can be tuned from red to blue. Moreover, CNC-polymer nanocomposite films can be prepared in a straightforward manner to produce cost-effective stretchable piezoelectric materials (d33>50 pC/N) that outperform PVDF and some ceramics. We have meticulously documented the structure-property interrelations influencing these responses, and have examined concentration, pH, ionic strength, and electromagnetic field effects. Our presentation will detail these fundamental criteria and how they influence performance and functionality in select end-use application platforms.

Resume : Developing a cellulosic fibre-based actuator opens up for new fields of cellulosic materials with added value and new types of applications. Being cellulosic potentially offers biodegradability and sustainability as well as low costs of any products. In addition, being textile leads to compatibility with the human body and pliability. Textiles can be transformed into actuators, where the textile construction enables guidance of the actuation direction and amplification of stress and strain. We have selected a regenerated cellulosic fiber (Lyocell) as the main substrate. Fibers were functionalized with nitrate functional groups and then electrostatic grafting of PEDOT:PSS onto cellulose nitrate fibers took place by a dip-coating method to provide electrical conductivity. PEDOT:PSS solution was modified with D-sorbitol and a non-ionic polyurethane-based thickener. Next, polypyrrole (PPy) was electro-synthesised to form a yarn actuator. Further, the impact of optimization of PEDOT:PSS solution, and the role of textile structures in the actuation mechanism, was studied. Using this, we achieved a highly stable conductive electrode coating. Optimization of PEDOT:PSS coating not only increased the conductivity of the E-textile (up to 75%) but also gives a stable electrochemical synthesis of PPy. As a result, the common large electrical conductivity drop during the redox reaction is prevented. We also studied the actuation mechanism of textile structures made. It was observed that the efficiency of actuation highly relies upon the fabric structure and its topology.

Resume : Laser induced graphene/graphite (LIG) is a method of converting a carbon rich precursor into highly conductive graphene using a laser. This method has shown great promise as a versatile and low-cost patterning technique. Here we show for the first time how an ink based on cellulose and lignin can be patterned using screen printing followed by laser graphitization. Screen printing is one of the most commonly used manufacturing techniques in printed electronics, making this approach compatible with existing processing of various devices. The use of forest-based materials opens the possibility of producing green and sustainable electronics and pre-patterning of the ink precursor enables carbon patterns without residual precursor between the patterns. We investigated the effect of the ink composition, laser parameters and additives on the conductivity and structure of the resulting carbon and could achieve record low sheet resistance of 3.8 Ω/sq and a surprisingly high degree of graphitization. We demonstrated that the process is compatible with printed electronics and finally manufactured a humidity sensor which uses lignin as the sensing layer and graphitized lignin as the electrodes.

Resume : Wearable sensors with a non-invasive platform have garnered significant interest over the recent years in the area of personalised healthcare monitoring. Extensive research is being carried out in this field as it utilises recent technology for the fabrication of smart sensors which aims in addressing the demands of epidermal sensing where durability, lightweight, and intimated skin conformance are core requirements. Yet, further progress in this area has been hindered due to the lack of efficient chemical sensors and biosensors, able to monitor the chemical constituents residing on the epidermis of the wearer’s body. In this context, electrochemical sensors offer promise as wearable chemical sensors due to their high performance, inherent miniaturization and low cost. A wide range of electrochemical sensors and biosensors have been developed for real-time non-invasive monitoring of electrolytes and metabolites in sweat, tears, saliva as indicator of wearer’s health status. Substantial progress in this field of electrochemical sensors has led to the development of commercial hand analysers such as ACCU-CHECK (Roche Diagnostics, Inc.), iSTAT (Abbot, Inc.), or Lactate Scout (Sports Resource Group, Inc.), for detecting metabolites and electrolytes. The present work demonstrates the fabrication and characterization of a wearable sensor which can help in real-time, non-invasive monitoring of metal ion levels (K+, Zn2+) in perspiration directly from human epidermis. Potassium, one of the major constituents in sweat after sodium is important for the normal functioning of the human body in regulating blood pressure, normal water balance, muscle contractions and maintain pH balance of the body. It is also an important electrolyte present in the human body. Deficiency in potassium can lead to high blood pressure, muscle paralysis, breathing problems, irregular heart rhythms and constipation. Zinc, another metal present in trace levels in human perspiration; is a primary biomarker for muscular stress and fatigue. It is an important trace metal ion as it is involved in functioning of biochemical processes relevant to enzymes, hormones, and transcription related factors. Perspiration represents an efficient pathway for the release of potassium and zinc which leads to its deficiency in the body. Thus, monitoring of these metal ions in the body from perspiration becomes essential for athletes and for persons engaged in strenuous physical activity for the detection of wide ranging physiological states. Changes of potassium concentration in perspiration beyond optimal concentration (0.2 g/l) and zinc (1.56 µg/ml) can be used as indicators for physiological state of human body, such as low blood pressure and muscular stress and fatigue. While identifying the loss of these metal ions during physical activity is very important, currently very few tools exist for real-time detection of metal ion levels in perspiration. Electrochemical techniques such as stripping voltammetry have also been employed extensively for qualitative and quantitative detection of metal ions from the body. In-situ measurements have been demonstrated using micro-fabricated three-electrode assemblies utilizing expensive and laborious lithographic techniques. Although miniaturized and portable, such systems are not reusable and therefore are expensive and not scalable. Besides, their integration for real-time monitoring has been a challenge. Thus, the need of the hour is a detection system that combines ease of handling, real-time, in-situ analysis and specific detection of these metal ions in perspiration without compromising on the sensitivity reusability and cost-effectiveness; thus paving the way for “Smart” diagnostics. In order to achieve this, we have utilized novel molecular nanomaterials as transducers onto which the ion-selective receptors were immobilized. Specifically, the detection assembly consisted of cellulose fibres that were conformally coated with single wall carbon nanotubes (SWNTs). This resulted in a synergistic relation with the cellulose matrix providing the porosity and SWNTs providing the high specific surface area and electrical conduction pathway for signal transduction resulting in the fabrication of CNT-thread. Achieving ultrahigh sensitivity over a wide concentration range of analyte has been a persistent, mutually exclusive challenge for real-time analytical detection and diagnostics. To this end, we demonstrate a miniaturized, coaxial, cable-type electrochemical sensor comprised of a carbon nanotube immobilized cellulose yarn (CNT-thread) to achieve ultrahigh sensitivity (<1 ppm) across a wide dynamic range (0.1−500 ppm) for the rapid (∼60 s) detection of K+ and Zn2+. The sensor comprises of two cables of CNT-thread, one coated with a polymeric, ion-receptor (tetrakis(p-aminophenyl) porphyrin for Zn2+) and Valinomycin for K+ acting as the working electrode and the other being a reference electrode of pristine CNT-thread. The sensor is extremely tolerant to interference (selectivity coefficient 10−3−10−5) from a wide range of cations (Na+, Mg2+, Cd2+, Ca2+, Fe2+, and Cu2+) and anions (Cl−, NO3−, PO43−, and CH3COO−) enabling real-time detection of K+ and Zn2+. Importantly, excellent signal consistency (<5% deviation) across multiple electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, and chronoamperometry is demonstrated. Minimal deviation (<6%) between the analyte concentrations estimated from the sensor and those estimated from atomic-absorption techniques is observed. Finally, the lifetime and mechanical sturdiness of the sensing platform is illustrated through elaborate experiments involving bending and seamless interfacing with human skin for non-invasive point-of-care analysis. Thus, this portable electrochemical platform enables the real-time analysis of metal ions in human perspiration without compromising on its sensitivity, reusability and cost-effectiveness. References [1] Bariya, Mallika., Nyein, Y.Y Hnin., Javey, Ali., Nature Electronics 2018, 162 , 160–171. [2] Heikenfeld, J. Nature 2016, 529, 475–476. [3] Mondal, S., Subramaniam, C., ACS Sustainable Chem. Eng. 2019, 7, 17, 14569-14579.

Resume : Increased energy demands have triggered efforts to explore new routes for fabricating energy efficient materials that combine efficient performance and environmentally friendly operation. Thermoelectric materials are promising candidates in this realm as they are able to transform waste heat into energy via a process involving zero emissions. Good thermoelectric performance requires good electrical conductivity coupled with low thermal conductivity. Current thermoelectric materials involve, for example, bismuth and selenium compounds tethered in layered structures. These elements are expensive and have toxicity issues. To tackle these challenges, this study aims at constructing hybrid films of advanced thermoelectric performance by combining the increased electrical conductivity of zinc oxide and the thermal insulation of cellulose, i.e., the most abundant biopolymer. Layer alternation was achieved via consequent steps of spin coating nanocellulose and atomic layer deposition of zinc oxide. The alternating organic/inorganic layers were characterized by atomic force microscopy and x-ray reflectivity. Electric and thermal conductivity measurements were applied to assess the thermoelectric performance of the multilayer structures. Overall, a new route of fabricating thermoelectric films was revealed.

Resume : In electrochemical energy storage devices, electrolyte solutions are essential. Alike electrodes, electrolytes also effect the performance such as specific energy, cyclic stability, longevity and self-discharge of device. Herein, we have synthesized a cost effective and environment friendly polyacrylic acid-based water in salt (WIS) electrolyte and used it to fabricate a device which include wood-based lignin with carbon as positive electrode and polyimide with carbon as negative electrode. The cost-effective biopolymers based pseudocapacitive device in WIS displayed a maximum of 16 Wh/kg specific energy, 6800 W/kg of power density, good cyclic stability (65% retention in specific capacity) up to 2500 cycles and remarkably slow self-discharge rate. The open circuit potential drops to 0.67 V from initial 1.7 V in 5 days. Our study can provide a facile pathway to assemble a cost-effective, environment friendly, stable and safe lignin based electrochemical energy storage device.

Resume : We report a fully printed (Direct-ink-Writing) nanocellulose-based supercapacitor with a specific capacitance of 5 F/g, a state-of-the-art performance for fully printed supercapacitors. With the exponentially growing number of sensors and connected-objects brought by the Internet-of-things era, the development of recyclable materials and sustainable manufacturing techniques is of crucial importance. The supercapacitor we present here is exclusively composed of biosourced materials and carbon. In particular, we use nanocellulose as a rheology modifier, structural material and binder in the development of several functional inks. The device is printed as two half-cells that are then folded together to form a 1 mm thick and 2.25 cm2 working device. Each half-cell is composed of four different layers: substrate, current collector, electrode and electrolyte. A substrate of plasticized cellulose is first printed, resulting in a low-surface roughness (2.5 μm RMS) and flexible substrate. A metal-free current-collector is printed on top of the substrate, exhibiting an electrical conductivity of 200 S/m and a surface resistance of 20 Ω/□. An hygroscopic cellulose-carbon electrode and a glycerol- NaCl electrolyte are subsequently printed on top of the current collectors. The materials and fabrication processes presented in this work advance the field of printed electronics and could be used for the fabrication of other passive and active components, from simple wiring to eco-friendly sensors.

Resume : The use of carbon-free renewable energy sources are needed to create a sustainable society. However, the two most popular sources of renewable energies; namely the solar and wind power are intermittent, they cannot match with the energy demand of human activity. Hence large-scale batteries are emerging as integral components of the energy solutions for the future to enable constant power delivery on the electrical grid. The current technologies for large scale electrical energy storage are based on the materials that have limited abundance or expensive to manufacture. In this regard, we report the development of a safe and sustainable bio-based battery components using materials that are abundant and recyclable. Lignin being one of the most abundant biopolymers, meets the requirement, as it has quinone-aromatic chemical groups that can be employed to store and deliver electrical charges by reversible Faradaic reactions. But lignin is also an electrical insulating material. To enable those Faradaic reactions, we composite lignin with a conducting polymer and obtain a nanocomposite that is conducting electricity and thus provide electrons and ions to lignin. More specifically, we report the preparation and optimization of the composite electrode containing lignosulfonate (LS) (lignin) and the conducting polymer (poly 3, 4-ethylenedioxythiophene; PEDOT) for energy storage application. Scaled-up synthesis route in aqueous media for low-cost environmentally friendly technology to make large volume batteries will be discussed. The results of the battery concept incorporating this lignin/PEDOT based-positrode) and a bio-based negatrode; PACA (poly(1-amino-5-chloroanthraquinone)/PEDOT in a water- based electrolyte along with cellulose based separator will be presented.

Resume : The conversion of biomass into valuable carbon composites as an efficient non-precious energy storage electrode material has elicited extensive research interests. As synthesized partially graphitized iron oxide-carbon composite material (Fe3O4/Fe3C@C) shows an excellent property as an electrode material for supercapacitor. X-ray diffraction analysis, high resolution transmission electron microscopy, X-ray photo-electron spectroscopy and Brunauer-Emmett-Teller analysis is used to study the structural, compositional and surface areal properties. The electrode material shows a specific surface area of 827.4 m2/g. Due to the synergistic effect of graphitic layers with iron oxide/carbide, Fe3O4/Fe3C@C hybrid electrode materials display high-performance for supercapacitor with excellent capacity of 878 F/g at a current density of 5 A/g (3-electrode) and 211.6 F/g at a current density of 0.4 A/g (2-electrode) in 6M KOH electrolyte with good cyclic stability.

Resume : Transparent wood with high strength and low thermal conductance has shown potential as an energy-saving building material with high optical transmittance. However, the transmittance degrades with material thickness due to high haze, which mainly stem from scattering of light at interfaces between the wooden template and the polymer matrix. In this work, such scattering interfaces were limited by introducing a low polymerization shrinkage thiol-ene thermoset as a matrix into a modified lignin wood template. The transparent wood was found to have a significantly lower haze due to favorable interactions between the thermoset and the modified lignin template. Delignified wood templates, commonly used for transparent wood, were also tested and did not show a similar decrease in haze.

Resume : There are many examples of development of devices, which use materials elaborated on the base of cellulose. Those are sensors, drives, flexible electronics components, etc. However, cellulose and derived materials are not often used or studied as optical systems or systems where optical phenomena can be inquired. The development of solar radiation dosimeters consisting of an organic dye and titanium oxide as a photocatalyst printed on the cellulose substrate is one of the examples. Cellulose fibers containing specific luminescent compounds as markers and simultaneously as effective modifiers for textile products, papers and plastic is other example. The aim of this work was to develop micro/nanostructured composites based on microcrystalline cellulose (MCC) as matrix and oxide compound as filler. The essential advantage of oxide fillers is their stability. In this work we described the procedure of synthesis, manufacturing, structural and optical (luminescent) characteristics of the MCC – oxide composites made by cold pressing method. Simple oxides (ZnO, ZrO2) as well as complex oxides (BiPO4:Eu; K2Eu(PO4)(MoO4)) were incorporated into MCC matrix. Some carbon species (CNT, graphen, expanded graphite) were added to the composites as modifiers. Characteristics of these composites were compared to characteristics of similar compositions prepared on the base of nanocellulose. The morphological, structural and optical, especially luminescence, characteristics were studied that confirmed the perspectives of practical application of the composites under study. The correlation between structural, morphological characteristics and physical properties of composites was found and discussed.

Resume : Transparent wood (TW) is an attractive cellulosic-based composite for optically transparent and structural applications. TW is obtained from native wood veneer via a three-step procedure that includes the removal of the lignin, modification of the delignified wood template, and subsequent infiltration by a polymer matrix with matching refractive index. However, the chemicals used to remove the lignin (e.g. sodium chlorite), modify the template (e.g. pyridine, DMF) and the infiltrated polymer systems (e.g. polymethyl methacrylate, epoxy) are petroleum-based and environmentally hazardous. This study presents a sustainable TW alternative with comparable materials properties as previously reported for petroleum-based TW composites. The fully bio-based TW was prepared via an environmentally friendly delignification method followed by a green surface activation of the template. Subsequently, a novel bio-renewable acrylic monomer was synthesized and infiltrated in the wood template. The morphology of the materials, the physical, optical and thermo-mechanical properties of the bio-based TW were investigated.

Resume : In pursuance of the Paris Agreement’s climate goals, our societies must promptly transition towards renewable energies. Unlike their fossil counterparts, renewable energies inherently rely on intermittent sources (i.e. sunlight, wind and tidal power) and need to be stored to further meet the variations of the electric demand on the power grid. Consequently, there is a growing societal need for the production of low-cost and high-capacity energy storage materials, preferably from renewable resources. The forest, pulp and paper industries could play a key role in this transition, possessing infrastructures designed for large-scale preparation of renewable materials and aiming at new high-added value applications for their wood-based products. Among the different available wood derivatives, cellulose nanofibers (CNFs) have shown great promise in the design of durable, environmentally friendly and high-capacity energy storage materials. Owing to their high aspect ratios (diameter = 4 nm, length = 1–5 µm), CNFs have unique colloidal properties that enable the preparation of materials showing a wide array of structures such as films, foams, aerogels or nanocomposites. These materials are readily functionalized with electrically-active materials, making them suitable for energy storage applications. For that purpose, conjugated polymers such as polyethylenedioxythiophene (PEDOT) are of a great interest, showing a high electrical conductivity as well as a great chemical affinity towards CNFs. In this study, we present a novel, efficient and environmentally friendly method for preparing nanoporous materials – also referred to as aerogels – from CNF and alginate, a biopolymer extracted from brown algae. Based on successive freezing, thawing and ambient-drying steps, this simple method could meet the industrial requirements both in terms of production rate and energy consumption. The present findings indicate that these aerogels can be given virtually any shape (using 3D-printing) while also displaying tunable microstructures and mechanical properties (by controlling the ionic conditions during preparation). Using a scalable in-situ polymerization procedure, the aerogels can be functionalized with high loadings of PEDOT nanoparticles (as high as 1.7 g g-1), providing them with high electronic conductivity (146 S m-1) and specific capacitance (78 F g-1) and consequently enabling their use as energy storage materials.

Resume : The polysaccharide cellulose is next to chitin the most abundant biopolymer on earth and is considered an almost inexhaustible source of raw material for the increasing demand for environmentally friendly and biocompatible products.[1] We recently synthesized a bio-based photoresist, where a photo-reactive cellulose-derivative is dissolved in an organic solvent together with a photoinitiator. This novel photoresist is curable by two-photon absorption at 780 nm in a direct laser writing (DLW) system (Nanoscribe Photonic Professional GT). With this setup, two-dimensional architectures with a linewidth of less than 250 nm and a minimum line distance of 500 nm are achieved. Our bio-based photoresist allows three-dimensional structuring of cellulose on the µm scale via DLW.[2] Curing of our cellulose derivative is generally possible in liquid and solid state via two-photon absorption. In contrast to common photoresists, which are based on polymers sourced from mineral oil, our approach conserves resources through replacing those polymers by sustainable materials such as polysaccharides. The presented research includes the functionalization of cellulose to enable photo-crosslinking for generating biopolymer-based hierarchical architectures. This chemical modification is a prerequisite for the fabrication of two- and three-dimensional structures by DLW. Disorder on the nano-scale is created by the surface roughness of the DLW-fabricated structures and can be tuned via the concentration of the photoinitiator. Moreover, this polysaccharide-based photoresist enables manufacturing of biomimetic architectures, which consist entirely of a natural bulking material. Additionally, this cellulosic photoresist is curable via one-photon absorption with a UV-lamp (365 nm) in liquid as well as in dried state. Our resist opens up a new class of photo-curable polymers based on sustainable and renewable materials. [1] D. Klemm, et al. Angew. Chem. Int. Ed. 2005, 44, 3358. [2] M. Rothammer, et al., Cellulose 2018, 25, 6031.

Resume : Concerns about sustainability, environ benignity in material science to develop new electrode materials have attracted a great interest in renewable materials from nature as emerging solutions to a range of technological challenges. In particular, bio-derived materials are not only biocompatible and earth-abundant but also have nature-provided intrinsic structures for potentially transformative impact. Herein, we are presenting the room temperature synthesis of lignin/cellulose based electrode material for energy storage device (e.g. supercapacitor). The as synthesized material shows capacitance ~1005 F/g at discharge current density of 2 A/g in 6M KOH as calculated using GCD. Such lignin/cellulose material has potential applications in development of sustainable, eco-friendly electrode material for energy application and for academic and industrial applications.

Resume : I this talk, I will discuss the use of direct laser writing on commercially available hydrophobic papers as a low cost and potentially scalable technique to rapidly prototype and manufacture a variety of microfluidic and transducing components and devices. Ubiquitous availability of cheap hydrophobic-layer-coated papers for culinary and food products combined with the bench-top lab-scale CO2 laser systems capable of selectively scanning and converting hydrophobic to hydrophilic regions allows for mask-less fabrication of disposable paper-based devices. After a brief description of the laser assisted fabrication technique, I will discuss several devices developed in my lab over the past few years including a variety of sensors targeted for interrogation of wound microenvironment. Next, I will describe a flexible smart wound dressing/patch capable of generation (via catalytic conversion of hydrogen peroxide delivered via a network of microfluidic channels) and sensing (via an integrated optical sensor) of oxygen fabricated using an integrated paper-PDMS platform. Finally, I will discuss challenges and opportunities in developing scalable manufacturing processes for successful commercialization of paper-based devices.

Resume : This talk will explore the new realm of using threads as an ultimate platform for flexible and stretchable devices. Threads offer unique advantages of universal availability, low cost, material diversity and simple textile-based processing. In this talk, I will report reel-to-reel fabrication to make functional smart threads for variety of sensing and electronics application. For example I will report on nanomaterial-infused smart threads for strain and temperature sensing. Threads will be presented for sensing pH, glucose, and other chemical biomarkers. Interestingly, threads also provide an ideal platform for passive microfluidic sampling and delivery of analytes. I will show our recent work on using this toolkit of thread-based microfluidics, sensors and electronics for application as surgical sutures and flexible smart bandages for chronic wounds. Our recent work on using threads for closed loop spatiotemporal dosage controlled drug delivery will also be presented. I will conclude the talk by providing an outlook on future research directions in the field of textile-based flexible bioelectronics.

Resume : With the rapid growth of wearable electronics and IoT, there is an increasing demand for compatible power sources such as wearable batteries. Organic biopolymer composites which combine electrical conductivity and redox activity have emerged as a promising class of electrode materials to realize cost-effective, eco-friendly and flexible batteries. However, the lack of stretchability and elasticity has limited their applications in wearable batteries that must function under dynamic and repetitive mechanical stresses. Here, we report a quaternary biocomposite that combines high electrical and ionic conductivity, originating from the conducting polymer and ionic liquid components, with the high energy storage capacity of nature-based quinones, and superior mechanical properties of a polyurethane elastomer matrix. The incorporation of multiple functionalities from different components was successfully achieved by the formation of favorable percolation networks and dynamic bonding between the components. Based on the strong adhesion of the polyurethane matrix, in combination with a polyether-polyurethane-ionic liquid electrolyte, we demonstrate all-organic solid-state stretchable batteries by laminating elastic electrodes and electrolyte produced from aqueous blends of composites.

Resume : Biodegradable electronic devices gain a lot of interest in research in the past years, since the negative influence of e-waste on our world and our quality of life is dramatically increasing. Among electronic devices, wearables are a rapidly growing field in research combining conformable, stretchable and electronic properties. Possible applications are electronic skin, on-skin diagnostics or displays. The branch of wearable electronics will benefit from up-scalable, low-cost production methods like printing techniques. Wearables will be considered disposable due to short lifecycles and therefore massively contribute to the amount of e-waste. The use of biomaterials in electronic devices is one way to enhance sustainability. Electrochromic devices thereby provide opportunities for developing low-cost, biodegradable display applications. They´re advantages are low power consumption, low operating voltages and a simple device architecture. Here, we present on a biodegradable, wearable electrochromic display, which was fully produced by inkjet printing. Furthermore, its biodegradability was validated according to the international standard ISO 14855, demonstrating the successful use of biomaterials in electronic devices. The electrochromic devices were fabricated on a biodegradable cellulose di-acetate substrate. Gold electrodes and the electrochromic poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer were deposited via inkjet-printing. Finally, the devices were encapsulated by a gelatin-based electrolyte. The influence of different natural salts on the device performance was investigated. The finalized electrochromic displays change reversibly between a transparent and a deep blue state with high contrast. Its adhesive and conformable properties enable the use of the displays as wearables directly on skin. The fabricated devices exhibit a sufficient contrast, efficiency and lifetime to be used in disposable, biofriendly consumer and health care applications.

Resume : Electronic textiles (e-textiles) attracted huge attention as they enable advances in numerous applications ranging from health monitoring sensors, energy storage, energy generators to wireless systems. Considering the advances in energy autonomy for digital health and self-health management and monitoring, e-textiles have potential scope in energy storage applications for powering the sensors and electronics in wearable systems. In this work we fabricated a wearable supercapacitor (SC) on cellulose/polyester based cloth with PEDOT: PSS electrode as an electrode. Here the PEDOT: PSS coated cloth act as both current collector and active material of the SC. We observed that, the excellent wet absorption capacity of the cloth due to the polyester content in it (55% cellulose and 45% polyester) adsorb the PEDOT: PSS solution in the bulk of cloth material. The electrochemical properties of the SCs were investigated in three type of electrolytes such as H3PO4, sweat (artificial and human) and room temperature ionic liquid. Among this, SC in H3PO4 electrolytes shows excellent performance (the lowest value of equivalent series resistance (ESR) is 2.2 Ω). However considering the wearability, SC in sweat shows more suitability with electrolytes biocompatibility and easy to replenishing. The fabricated SC shows energy and power density of 1.36 Wh. kg-1 (1.63 µWh.cm-2) and 329.70 W.kg-1 (0.40 mWcm-2) respectively for 1.31 V (its specific capacitance 5.65 F.g-1) in an artificial sweat.

Resume : Electronic textiles are fabrics that have incorporated electronics for medicine, health monitoring and other functional purposes. Using wood cellulose in electronic textiles will enable comfortable, biocompatible and sustainable products. In this work, a new and efficient nonwoven technique solution blown was used to produce flexible conductive wood cellulose nonwovens. This technique introduces conductive carbon black (CB) nanoparticles in the cellulose solutions prior the fiber formation. The flexible and continuously regenerated cellulose/CB fiber filaments were formed by extruding the solution through multiple micro-nozzles and drawn by high velocity air to form fiber networks. The process allows versatile tailoring of functionalities of the cellulose and varying of the microstructures and the porosity of the nonwoven. The relationships between the material properties and process parameters have been explored. The scanning electron microscopy study showed that the CB and cellulose were combined homogenously; the fiber diameters were varied from 1-100 µm for different processes. For the nonwovens with the same CB/cellulose ratio, the 4-point probe measurements showed that the area resistance was decreased from ca. 5000 Ω/□ to 700 Ω/□ with decreased porosity. The moisture content also showed effect on the area resistance. The nonwoven has charge storage capability. Promising applications include, e.g., energy storage, moisture sensors and near body heater.

Resume : Cotton is established as an innovative foundation for smart wearable energy storage devices with appealing properties. The challenge is that the current approaches using either additional coating or direct carbonization mostly lead to mechanically fragile or electrochemically poor textile. We demonstrate that the coating of metal oxide on the cotton and subsequent pyrolysis readily turn cotton into the conductive textile with high porosity and excellent toughness. The resulting textile has an energy density of 2.24 mWh/cm3 (nearly 3 times higher than other commercial supercapacitors) and a power density of 585 mW/cm3 (over 2-orders-of-magnitude higher than that of the lithium battery). We show that the metal oxide assisted carbonization allows metal atoms to migrate into the graphite-like layers of the carbonized cotton. It appears that the migrated metal atoms and the phase transformation of the coated metal oxides play a critical role in considerable changes in the microstructure and porosity of the carbonized cotton.

Resume : Due to the intensive growth of electronics and telecommunications, electromagnetic (EM) pollution has become a serious concern of the modern world. Apart from the public health impact of EM pollution, such as brain tumor and leukemia, it also causes interference to the working of many nearby devices. In this regard, wearable electromagnetic interference (EMI) shielding materials such as conducting textiles have emerged to protect human as well as sensitive electronics from EM pollution. In this work, zinc oxide (ZnO) and reduced graphene oxide (rGO) coated wearable cellulose-based textile are prepared for the application of EMI shielding in X-band (8.2-12.4 GHz). The uniform coating of ZnO nanoparticles is achieved by the in-situ sol-gel method, whereas the uniform coating of rGO is achieved by simple spraying of graphene oxide solution followed by thermal reduction. The total EMI shielding effectiveness increases with the rGO loading, however, the return loss decreases owing to improved conductivity of the fabric. The as-prepared rGO/ZnO coated cotton achieves high total EMI shielding effectiveness of ~99.999% (54.7 dB), which is shared by ~17.783% of reflection and ~82.216% of absorption. Such high absorption dominant EMI shielding is attributed to highly conductive rGO sheets, highly dielectric ZnO nanoparticles and the core-shell structure of the coated cotton fabric. Keywords: Cellulose-based composites, Wearable electro-conductive textile, EMI shielding