Yangyang Han

Highly Sensitive, Stretchable, and Wash-Durable Strain Sensor Based on Ultrathin Conductive Layer@Polyurethane Yarn for Tiny Motion Monitoring

Strain sensors play an important role in the next generation of artificially intelligent products. However, it is difficult to achieve a good balance between the desirable performance and the easy-to-produce requirement of strain sensors. In this work, we proposed a simple, cost-efficient, and large-area compliant strategy for fabricating highly sensitive strain sensor by coating a polyurethane (PU) yarn with an ultrathin, elastic, and robust conductive polymer composite (CPC) layer consisting of carbon black and natural rubber. This CPC@PU yarn strain sensor exhibited high sensitivity with a gauge factor of 39 and detection limit of 0.1% strain. The elasticity and robustness of the CPC layer endowed the sensor with good reproducibility over 10,000 cycles and excellent wash- and corrosion-resistance. We confirmed the applicability of our strain sensor in monitoring tiny human motions. The results indicated that tiny normal physiological activities (including pronunciation, pulse, expression, swallowing, coughing, etc.) could be monitored using this CPC@PU sensor in real time. In particular, the pronunciation could be well parsed from the recorded delicate speech patterns, and the emotions of laughing and crying could be detected and distinguished using this sensor. Moreover, this CPC@PU strain-sensitive yarn could be woven into textiles to produce functional electronic fabrics. The high sensitivity and washing durability of this CPC@PU yarn strain sensor, together with its low-cost, simplicity, and environmental friendliness in fabrication, open up new opportunities for cost-efficient fabrication of high performance strain sensing devices.

Flexible, highly transparent and iridescent all-cellulose hybrid nanopaper with enhanced mechanical strength and writable surface.

With the development of flexible electronic devices, there is increasing requirement for the inexpensive and environmental-friendly substrates. Cellulose paper has gained great attention because of its abundance, biodegradability and renewability. In this paper, we designed a hybrid nanopaper by introducing native cellulose nanofibrils (CNFs) into cellulose nanowhiskers (CNWs) matrix, which achieved a high optical transmittance while retaining iridescence under polarizing film. This nanopaper is less expensive than neat CNFs-based nanopaper and more feasible for large-scale production. Besides, our transparent hybrid nanopaper possesses the writable surface like regular paper. Compared with commercial paper, however, hybrid nanopaper shows superior optical properties and low surface roughness. The combination of these characteristics makes this nanopaper an excellent candidate for substrates of flexible electronic devices.

Self-Healing, Highly Sensitive Electronic Sensors Enabled by Metal–Ligand Coordination and Hierarchical Structure Design

Electronic sensors capable of capturing mechanical deformation are highly desirable for the next generation of artificial intelligence products. However, it remains a challenge to prepare self-healing, highly sensitive, and cost-efficient sensors for both tiny and large human motion monitoring. Here, a new kind of self-healing, sensitive, and versatile strain sensors has been developed by combining metal-ligand chemistry with hierarchical structure design. Specifically, a self-healing and nanostructured conductive layer is deposited onto a self-healing elastomer substrate cross-linked by metal-ligand coordinate bonds, forming a hierarchically structured sensor. The resultant sensors exhibit high sensitivity, low detection limit (0.05% strain), remarkable self-healing capability, as well as excellent reproducibility. Notably, the self-healed sensors are still capable to precisely capture not only tiny physiological activities (such as speech, swallowing, and coughing) but also large human motions (finger and neck bending, touching). Moreover, harsh treatments, including bending over 50000 times and mechanical washing, could not influence the sensitivity and stability of the self-healed sensors in human motion monitoring. This proposed strategy via alliance of metal-ligand chemistry and hierarchical structure design represents a general approach to manufacturing self-healing, robust sensors, and other electronic devices.

Biological phytic acid as a multifunctional curing agent for elastomers: towards skin-touchable and flame retardant electronic sensors

Strain sensors have attracted extensive attention for wearable electronic applications. However, for many reported electronic sensors, the utilization of noxious agents brings about potential damage to human health and the inferior flame retardance increases the risk of circuits burning out. In this work, a skin-touchable and flame retardant electronic sensor is fabricated by integrating green chemistry with nanostructure design. Specifically, renewable and biocompatible phytic acid (PA) is used as a multifunctional curing agent to cross-link epoxidized natural rubber for the first time and the obtained elastomer exhibits excellent mechanical and flame retarding properties. Then, an electronic sensor is prepared by depositing a nanostructured conductive layer on the elastomer substrate for human-motion monitoring. The resultant sensor shows the abilities to precisely detect not only large-scale physiological activities (finger and wrist bending) but also small-scale human motions (such as speech, coughing and expression). Notably, the electronic sensor is capable of self-extinguishing after ignition owing to the presence of phosphorus-rich groups in the PA-cured elastomer and could come into contact with the skin at liberty. This highly sensitive, skin-touchable and noncombustible electronic sensor, together with its simplicity and eco-friendliness in fabrication, is attractive for next generation wearable electronics.

Spirally Structured Conductive Composites for Highly Stretchable, Robust Conductors and Sensors

Flexible and stretchable electronics are highly desirable for next generation devices. However, stretchability and conductivity are fundamentally difficult to combine for conventional conductive composites, which restricts their widespread applications especially as stretchable electronics. Here, we innovatively develop a new class of highly stretchable and robust conductive composites via a simple and scalable structural approach. Briefly, carbon nanotubes are spray-coated onto a self-adhesive rubber film, followed by rolling up the film completely to create a spirally layered structure within the composites. This unique spirally layered structure breaks the typical trade-off between stretchability and conductivity of traditional conductive composites and, more importantly, restrains the generation and propagation of mechanical microcracks in the conductive layer under strain. Benefiting from such structure-induced advantages, the spirally layered composites exhibit high stretchability and flexibility, good conductive stability, and excellent robustness, enabling the composites to serve as highly stretchable conductors (up to 300% strain), versatile sensors for monitoring both subtle and large human activities, and functional threads for wearable electronics. This novel and efficient methodology provides a new design philosophy for manufacturing not only stretchable conductors and sensors but also other stretchable electronics, such as transistors, generators, artificial muscles, etc.

In situ doping enables the multifunctionalization of templately synthesized polyaniline@cellulose nanocomposites

Cellulose aerogels have been widely studied as promising environmentally friendly materials due to their low density, biocompatibility and degradability. However, their applications are limited due to their highly combustible nature. In this study, polyaniline (PANI) decorated bacterial cellulose (BC) composite aerogel has been synthesized with in situ polymerization of aniline monomer on the surface of BC scaffold. The PANI decorated BC composite aerogel has a very high specific area of 124.0m2/g and well-preserved nanoporous structure, while its conductivity drastically increased to 10.44S/m. Interestingly, phosphate groups were incorporated onto PANI backbones due to its unique doping/dedoping structure. The resultant composite aerogel presented excellent flame retardancy, which can be self-extinguished within 1s. Moreover, PANI@BC composite hydrogel exhibited self-motion behavior under low voltage electric field, illustrating potential electromechanical actuator application. This simple and sustainable in situ doping method opens up new opportunities for cost-efficient fabrication of multifunctional cellulose-based electronics.