Fiber Surface/Interfacial Engineering on Wearable Electronics

Zebra-Patterned Stretchable Helical Yarn for Triboelectric Self-Powered Multifunctional Sensing

Smart textiles capable of both energy harvesting and multifunctional sensing are highly desirable for next-generation portable electronics. However, there are still challenges that need to be conquered, such as the innovation of an energy-harvesting model and the optimization of interface bonding between fibers and active materials. Herein, inspired by the spiral structure of natural vines, a highly stretchable triboelectric helical yarn (TEHY) was manufactured by twisting the carbon nanotube/polyurethane nanofiber (CNT/PU NF) Janus membrane. The TEHY had a zebra-stripe-like design that was composed of black interval conductive CNTs and white insulative PU NFs. Due to the different electron affinity, the zebra-patterned TEHY realized a self-frictional triboelectric effect because the numerous microscopic CNT/PU triboelectric interfaces generated an alternating current in the external conductive circuit without extra external friction layers. The helical geometry combined with the elastic PU matrix endowed TEHY with superelastic stretchability and outstanding output stability after 1000 cycles of the stretch-release test. By virtue of the robust mechanical and electrical stability, the TEHY can not only be used as a high-entropy mechanical energy harvester but also serve as a self-powered sensor to monitor the stretching or deforming stimuli and human physiological activities in real time. These merits manifested the versatile applications of TEHY in smart fabrics, wearable power supplies, and human-machine interactions.

Preparation of a Novel Formaldehyde-Free Impregnated Decorative Paper Containing MnO2 Nanoparticles for Highly Efficient Formaldehyde Removal

The loading of catalytic manganese dioxide (MnO₂) nanoparticles onto an impregnated decorative paper has been an effective method for the removal of indoor formaldehyde (HCHO) pollutants. However, its preparation can present numerous challenges, including instability in dipping emulsions and leaching. In this investigation, a novel and stable formaldehyde-free polyacrylate dipping emulsion containing MnO₂ particles was prepared and then back-coated on a decorative paper. To improve the dispersion and fixation, the MnO₂ was modified with silane. HCHO can undergo physical adsorption on the cellulosic fibers present in the paper, while it can also undergo chemical degradation into CO₂ within the MnO₂ groups. The silane not only enhanced the interfacial adhesion to a polyacrylate resin but also increased the interlayer distance, thereby creating a larger space for HCHO absorption. The impregnated decorative paper back-coated with 10 wt % of silane-modified MnO₂ exhibited a removal efficiency of approximately 90% for HCHO at 20 °C. The removal rate further improved to approximately 100% when the temperature was increased to 60 °C. Moreover, it is worth noting that the release of volatile organic compounds was exceptionally minimal. Additionally, the particleboard bonded with this impregnated decorative paper exhibited an extremely low emission of HCHO, with a value that approached 0 mg·L^-1. Furthermore, the bonding strength of the surface remained unaffected. Therefore, this study provides a simple and eco-friendly method for effectively removing HCHO, which can enhance indoor air quality.

Surface Mechanical Properties and Topological Characteristics of Thermoplastic Copolyesters after Precisely Controlled Abrasion

Due to the high probability of surface-to-surface contact of materials during routine applications, surface abrasion remains one of the most challenging factors governing the long-term performance of polymeric materials due to their broad range of tunable mechanical properties, as well as the varied conditions of abrasion (regarding, e.g., rate, load, and contact area). While this concept is empirically mature, a fundamental understanding of mechanical abrasion regarding thermoplastics remains lacking even though polymer abrasion can inadvertently lead to the formation of nano-/microplastics. In the present study, we introduce the concept of precision polymer abrasion (PPA) in conjunction with nanoindentation to elucidate the extent to which controlled wear is experienced by three chemically related thermoplastics under systematically varied abrasion conditions. While depth profiling of one polymer reveals a probe-dependent change in modulus, complementary results from positron annihilation lifetime spectroscopy confirm that the polymer density changes measurably, but not appreciably, with depth over the depth range explored. After a single PPA pass, the surface moduli of the polymers noticeably increase, whereas the corresponding increase in hardness is modest. The dependence of wear volume on the number of PPA passes is observed to reach limiting values for two of the thermoplastics, and application of an empirical model to the data yields estimates of these values for all three thermoplastics. These results suggest that the metrics commonly employed to describe the surface abrasion of polymers requires careful consideration of a host of underlying factors.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

Fast and Integral Nano-Surface-Coating of Various Fiber Materials via Interfacial Polymerization

Surface coating is essential and critical to endow fiber materials with various functions for broad applications. However, it is still a great challenge to achieve a fast, fully covered, and robust surface coating on multiple fibers. In this work, a nanoscale surface coating with superior stability was rapidly and integrally formed on various fiber materials (such as Nylon mesh, nonwoven fabrics, and stainless-steel mesh) by highly reactive interfacial polymerization (IP) between polyethylenimine (PEI) and trimesoyl chloride (TMC). The resulting polyamide (PA) layer with an ultrathin thickness of tens of nanometers wholly and uniformly covered the surface of each fiber of the constituent material. Due to the synergistic effect of the PA layer with inherent robustness and the fully covered structure between the outer PA layer and the inner fiber, the nanosurface-coating exhibited outstanding mechanical stability, good acid resistance, and excellent organic solvent resistance. The functional modification of the nanosurface-coating can be easily carried out by using the abundant carboxyl groups in the PA layer. By introducing sulfobetaine zwitterionic copolymers via either "grafting from" or "grafting to" methods, the surfaces presented prominent underwater antioil-adhesion property and exceptional protein adhesion resistance. The surface coating based on IP process opens up an avenue in the field of surface modification. It is expected to offer a generally feasible strategy for the fabrication of fiber materials with robust and multifunctional coatings.

Piezoresistive Fibers with Large Working Factors for Strain Sensing Applications

Piezoresistive fibers with large working factors remain of great interest for strain sensing applications involving large strains, yet difficult to achieve. Here, we produced strain-sensitive fibers with large working factors by dip-coating nanocomposite piezoresistive inks on surface-modified polyether block amide (PEBA) fibers. Surface modification of neat PEBA fibers was carried out with polydopamine (PDA) while nanocomposite conductive inks consisted of styrene-ethylene-butylene-styrene (SEBS) elastomer and carbon black (CB). As such, the deposition of piezoresistive coatings was enabled through nonconventional hydrogen-bonding interactions. The resultant fibers demonstrated well-defined piezoresistive linear relationships, which increased with CB filler loading in SEBS. In addition, gauge factors decreased with increasing CB mass fractions from ∼15 to ∼7. Furthermore, we used the fatigue theory to predict the endurance limit (C_e) of our fibers toward resistance signal stability. Such a piezoresistive performance allowed us to explore the application of our fibers as strain sensors for monitoring the movement of finger joints.

Recent Advances in ZIF-Derived Atomic Metal-N-C Electrocatalysts for Oxygen Reduction Reaction: Synthetic Strategies, Active Centers, and Stabilities

Exploring highly active, stable electrocatalysts with earth-abundant metal centers for the oxygen reduction reaction (ORR) is essential for sustainable energy conversion. Due to the high cost and scarcity of platinum, it is a general trend to develop metal-N-C (M-N-C) electrocatalysts, especially those prepared from the zeolite imidazolate framework (ZIF) to replace/minimize usage of noble metals in ORR electrocatalysis for their amazingly high catalytic efficiency, great stability, and readily-tuned electronic structure. In this review, the most pivotal advances in mechanisms leading to declined catalytic performance, synthetic strategies, and design principles in engineering ZIF-derived M-N-C for efficient ORR catalysis, are presented. Notably, this review focuses on how to improve intrinsic ORR activity, such as M-N_x -C_y coordination structures, doping metal-free heteroatoms in M-N-C, dual/multi-metal sites, hydrogen passivation, and edge-hosted M-N_x . Meanwhile, how to increase active sites density, including formation of M-N complex, spatial confinement effects, and porous structure design, are discussed. Thereafter, challenges and future perspectives of M-N-C are also proposed. The authors believe this instructive review will provide experimental and theoretical guidance for designing future, highly active ORR electrocatalysts, and facilitate their applications in diverse ORR-related energy technologies.