Novel Retroreflective Structural Color Films Based on Total Internal Reflection Interference.

Structural color materials have tremendous applications and been extensively investigated in the past decades. Most of them involve either nanoscale periodic photonic crystal structure or film interference mechanisms. Herein, we report a novel retroreflective structural color film (RSCF) based on a combined effect of interference and total internal reflection (TIR). The RSCF is consisted of a microscale polymer hemisphere array formed on the same polymer matrix. When exposed to white light illumination, the non-hemisphere-side of the film exhibits non-iridescent color under coaxial illumination and observation, and iridescent color under noncoaxial illumination and observation. In contrary, the hemisphere-side of the film does not show any colors regardless of coaxial or noncoaxial illumination and observation. Furthermore, an elastic polyurethane-based RSCF can exhibit dynamically and reversibly changing colors during uniaxial tensile/compressive deformation.

Full-Textile Human Motion Detection Systems Integrated by Facile Weaving with Hierarchical Core-Shell Piezoresistive Yarns.

The tremendous progress of the wearable intelligent system has brought an urgent demand for flexible pressure sensors, especially for those possessing high sensing performances, simple manufacture technology, and efficient integration. In this work, hierarchical core-shell piezoresistive yarns (HCPYs), which contain internal silver-plated nylon electrodes and surface microporous structured carbon nanotubes (CNTs)/thermoplastic polyurethane (TPU) sensing layer, are designed and manufactured via facile wet-spinning accompanied by a water vapor coagulating bath. The obtained HCPY can either be inserted into traditional textiles to assemble a single-pressure sensor, or be woven into a textile-based flexible pressure sensors array with expected size and resolution, without compromising their comfort, breathability, and three-dimensional (3D) conformability. Simultaneously, to further enhance the sensing performance, the surface microporous structures of HCPYs are optimized by altering the treatment humidity and exposure time during the process of water vapor-induced phase separation. The wearable pressure sensors assembled by the optimal HCPY achieved a high sensitivity up to 84.5 N-1, a good durability over 5000-cycle tests, a fast response time of 2.1 ms, and a recovery time of 2.4 ms. Moreover, the wearable pressure sensors have been successfully used to monitor physical signals and human motions. The textile-based flexible pressure sensors array has also been seamlessly integrated with sportswear to detect movements of the elbow joint and map spatial pressure distribution, which makes HCPY a promising candidate for constructing next-generation wearable electronics.

Breathable and Large Curved Area Perceptible Flexible Piezoresistive Sensors Fabricated with Conductive Nanofiber Assemblies.

The rapid development of wearable electronics, humanoid robots, and artificial intelligence requires sensors to sensitively and stably detect external stress variations in large areas or on three-dimensional (3D) irregularly shaped surfaces while possessing the comfort. Most importantly, the flexibility and 3D compliance of sensors, and the fitting state of the interface between the sensor and the object are of great significance to the sensing accuracy and reliability. The ordered or random stacking and entangling of flexible and electrically conductive fiber materials can form a highly porous and mechanically stable fiber assembly. The changes in external stress can lead to the air trapped in the fiber assembly to flow in and out rapidly and repeatedly, as well as the reversible mechanical deformation of fiber materials. Correspondingly, the contact areas between electrically conductive fibers in the fiber assembly are reversibly changed, which makes the conductive and flexible fiber assembly be an ideal candidate for piezoresistive sensing material. It can be further expected that the statistical stability of contact points between conductive fibers under the stress may significantly increase with the decrease in fiber diameters. Herein, a new method to make a flexible piezoresistive sensor with conductive and porous fiber assembly was proposed. An ultrasensitive piezoresistive material was facilely prepared by fabricating conductive poly(vinyl alcohol-co-ethylene) (EVOH) nanofiber assemblies. The sensing performance of the piezoresistive sensor was optimized by regulating the nanofiber morphology, electrical conductivity, and mechanical properties. The flexible piezoresistive sensor exhibited a sensitivity of 2.79 kPa-1, a response time of 3 ms, and a recovery time of 10 ms. The sensing performance at different working frequencies was stable and durable within 4500 cycling tests. The flexible sensor showed good pressure-sensing accuracy and reliability when used on irregular surfaces and therefore was further applied in the static monitoring of large-area spatial pressure distribution and the wearable intelligent interactive device, demonstrating great application potential.