Multifunctional resistive-heating and color-changing monofilaments produced by a single-step coaxial melt-spinning process

Multi-Stimuli Dually-Responsive Intelligent Woven Structures with Local Programmability for Biomimetic Applications

This work focuses on multi-stimuli-responsive materials with distinctive abilities, that is, color-changing and shape-memory. Using metallic composite yarns and polymeric/thermochromic microcapsule composite fibers, processed via a melt-spinning technique, an electrothermally multi-responsive fabric is woven. The resulting smart-fabric transfers from a predefined structure to an original shape while changing color upon heating or applying an electric field, making it appealing for advanced applications. The shape-memory and color-changing features of the fabric can be controlled by rationally controlling the micro-scale design of the individual fibers in the structure. Thus, the fibers' microstructural features are optimized to achieve excellent color-changing behavior along with shape fixity and recovery ratios of 99.95% and 79.2%, respectively. More importantly, the fabric's dual-response by electric field can be achieved by a low voltage of 5 V, which is smaller than the previously reported values. Above and beyond, the fabric is able to be meticulously activated by selectively applying a controlled voltage to any part of the fabric. The precise local responsiveness can be bestowed upon the fabric by readily controlling its macro-scale design. A biomimetic dragonfly with the shape-memory and color-changing dual-response ability is successfully fabricated, broadening the design and fabrication horizon of groundbreaking smart materials with multiple functions.

Tethering of twisted-fiber artificial muscles

Twisted-fiber artificial muscles, a new type of soft actuator, exhibit significant potential for use in applications related to lightweight smart devices and soft robotics. Fiber twisting generates internal torque and a spiral architecture, exhibiting rotation, contraction, or elongation as a result of fiber volume change. Untethering a twisted fiber often results in fiber untwisting and loss of stored torque energy. Preserving the torque in twisted fibers during actuation is necessary to realize a reversible and stable artificial muscle performance; this is a key issue that has not yet been systematically discussed and reviewed. This review summarizes the mechanisms for preserving the torque within twisted fibers and the potential applications of such systems. The potential challenges and future directions of research related to twisted-fiber artificial muscles are also discussed.

The Electrical-Triggered High Contrast and Reversible Color-Changing Janus Fabric Based on Double Side Coating

A sensitive electro-thermochromic Janus fabric driven by voltage is demonstrated via a facial double side coating. The graphene forms a conductive layer that allows Joule heating to supply the thermal resource for the electro-thermochromic behavior of polyester fabric. The thermochromic dye with reversible color-changing property is coated on the opposite side of the graphene layer. The color of electro-thermochromic Janus fabric changes from blue to white with a gradual heating that exceeded 45 °C at the applied voltage of 10 V. The switching rate of color is rapid with the increase of temperature from the room temperature to above 45 °C in 8 s, resulting from the superior resistive heating of the graphene. The electrical conductivity of the electro-thermochromic Janus fabric is not disturbed once undergoing a bending angle range from 30° to 150° and the temperature remains stable after 1000 bending cycles which clearly indicates the excellent flexibility of the fabric. The steady signal in the heating/cooling curve is observed after 500 cycles, pointing out the outstanding durability of the electro-thermochromic Janus fabric under the supplied voltage. It is realizable that the color of electro-thermochromic Janus fabric is triggered accurately by varying the supplied voltage. The simplicity of this design makes it attractive for the application of flexible electro-thermochromic textile, such as active visual camouflage, personal thermal management, and information displays.

Coaxial Spinning of All-Cellulose Systems for Enhanced Toughness: Filaments of Oxidized Nanofibrils Sheathed in Cellulose II Regenerated from a Protic Ionic Liquid

Hydrogels of TEMPO-oxidized nanocellulose were stabilized for dry-jet wet spinning using a shell of cellulose dissolved in 1,5-diazabicyclo[4.3.0]non-5-enium propionate ([DBNH][CO₂Et]), a protic ionic liquid (PIL). Coagulation in an acidic water bath resulted in continuous core-shell filaments (CSFs) that were tough and flexible with an average dry (and wet) toughness of ∼11 (2) MJ·m^-3 and elongation of ∼9 (14) %. The CSF morphology, chemical composition, thermal stability, crystallinity, and bacterial activity were assessed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, liquid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, pyrolysis gas chromatography-mass spectrometry, wide-angle X-ray scattering, and bacterial cell culturing, respectively. The coaxial wet spinning yields PIL-free systems carrying on the surface the cellulose II polymorph, which not only enhances the toughness of the filaments but facilities their functionalization.

Continuous and rapid fabrication of photochromic fibers by facilely coating tungsten oxide/polyvinyl alcohol composites

Photochromic fibers have attracted great attention due to their wide use in areas of military camouflage, safety warnings, anti-counterfeiting, entertainment, etc. Compared with photochromic organic materials, inorganic photochromic tungsten trioxide (WO₃) materials have been extensively studied, because of their good stability and cost efficiency. In this work, we report the continuous fabrication of photochromic fibers in a simple and low-cost way by dip-coating WO₃/PVA composites. The prepared photochromic fibers show fast and reversible color switch from light yellow to dark blue upon UV irradiation and infrared heating treatment. The obtained photochromic fibers can be produced on a large scale and be woven into various patterns with good mechanical strength and washability, showing great potential in developing photochromic textiles.

Photochromic fibers have attracted great attention due to their wide use in areas of military camouflage, safety warnings, anti-counterfeiting, entertainment, etc.

Red, green, blue (RGB) electrochromic fibers for the new smart color change fabrics

These fibers are prepared using stainless steel wires (SSWs) as a substrate. Three kinds of electrochromic materials (poly(3,4-ethylenedioxythiophene), poly(3-methylthiophene), and poly(2,5-dimethoxyaniline)) are quickly deposited on the surface of the SSWs by electrochemical polymerization. A polymer gel electrolyte is then coated onto the electrochromic layer, and another finer stainless steel wire is twisted on, in succession. The obvious RGB colors and gradient color phenomenon from gray to dark blue are observed by the naked eye besides color changes from oxidized to reduced states. Moreover, these electrochromic fibers have very short response times (millisecond scale), excellent flexibility, and good structural stability even though the bending and folding occurred. They also can be implanted into fabrics to achieve more color combinations through regulating the voltages and parallel connection of different circuits.