Piezoelectric polymers, capable of converting mechanical vibrations into electrical energy, are attractive for use in vibrational energy harvesting due to their flexibility, robustness, ease and low cost of fabrication. In particular, piezoelectric polymers nanostructures have been found to exhibit higher crystallinity, higher piezoelectric coefficients and 'self-poling', as compared to films or bulk. The research in this area has been mainly dominated by polyvinylidene fluoride (PVDF) and its co-polymers, which while promising, have a limited temperature range of operation due to their low Curie and/or melting temperatures. Here, we report the fabrication and properties of vertically aligned, and 'self-poled' piezoelectric Nylon-11 nanowires with a melting temperature of ~200 °C, grown by a facile and scalable capillary wetting technique. We show that a simple nanogenerator comprising as-grown Nylon-11 nanowires, embedded in an anodized alumina (AAO) template, can produce an open-circuit voltage of 1 V and short-circuit current of 100 nA, when subjected to small-amplitude, low-frequency vibrations. Importantly, the resulting nanogenerator is shown to exhibit excellent fatigue performance and high temperature stability. Our work thus offers the possibility of exploiting a previously unexplored low-cost piezoelectric polymer for nanowire-based energy harvesting, particularly at temperatures well above room-temperature.

Polypyrrole (Ppy) hydrogels are a promising new avenue for developing cheap wearable electronics and biotechnology. In particular, the use of conducting polymer hydrogels can impart elasticity and a high specific surface area, leading to great potential for sensors, cell growth scaffolds, and energy storage. However, their significantly low conductivity (compared to Ppy films and carbon or metallic microstructures), hydrophobicity, and low adhesiveness mean that they are currently unsuitable for most biological and wearable applications. Here, we show that by electropolymerizing a covalently bonded polydopamine (PDA) phase within polypyrrole hydrogels, we increased the conductivity by 2720% and adhesion by 2140% compared to pure polypyrrole hydrogels. Pyrrole monomers provided π-bond stabilization and prevented a π-stacked, auto-oxidized layer of PDA from forming. Instead, through potentiodynamic polarization of polypyrrole gels after dopamine incorporation, we produced covalently bonded 5,6-dihydroxyindole, producing an additional phase of conjugated polymer that interacted with the polypyrrole through noncovalent bonding. The PDA’s unoxidized catechol groups also led to increased hydrophilicity and adhesiveness of the hydrogels. These results are a further step toward the realization of fully polymer wearable electronics made with a simple, scalable technique, thereby removing the need for expensive, biologically unfriendly metals or carbon structures.

Flexibility plays a vital role in wearable electronics. Repeated bending often leads to the dramatic decrease of conductivity because of the numerous microcracks formed in the metal coating layer, which is undesirable for flexible conductors. Herein, conductive textile‐based tactile sensors and metal‐coated polyurethane sponge‐based bending sensors with superior flexibility for monitoring human touch and arm motions are proposed, respectively. Tannic acid, a traditional mordant, is introduced to attach to various flexible substrates, providing a perfect platform for catalyst absorbing and subsequent electroless deposition (ELD). By understanding the nucleation, growth, and structure of electroless metal deposits, the surface morphology of metal nanoparticles can be controlled in nanoscale with simple variation of the plating time. When the electroless plating time is 20 min, the normalized resistance (R/R0) of as‐made conductive fibers is only 1.6, which is much lower than a 60 min ELD sample at the same conditions (R/R0 ≈ 5). This is because a large number of unfilled gaps between nanoparticles prevent metal films from cracking under bending. Importantly, the Kelvin problem is relevant to deposited conductive coatings because metallic cells have a honeycomb‐like structure, which is a rationale to explain the relationships of conductivity and flexibility.

Intelligent human-machine interfaces (HMIs) integrated wearable electronics are essential to promote the Internet of Things (IoT). Herein, a curcumin-assisted electroless deposition technology is developed for the first time to achieve stretchable strain sensing yarns (SSSYs) with high conductivity (0.2 Ω cm −1) and ultralight weight (1.5 mg cm −1). The isotropically deposited structural yarns can bear high uniaxial elongation (>>1100%) and still retain low resistivity after 5000 continuous stretching-releasing cycles under 50% strain. Apart from the high flexibility enabled by helical loaded structure, a precise strain sensing function can be facilitated under external forces with metal-coated conductive layers. Based on the mechanics analysis, the strain sensing responses are scaled with the dependences on structural variables and show good agreements with the experimental results. The application of interfacial enhanced yarns as wearable logic HMIs to remotely control the robotic hand and manipulate the color switching of light on the basis of gesture recognition is demonstrated. It is hoped that the SSSYs strategy can shed an extra light in future HMIs development and incoming IoT and artificial intelligence technologies.

particular 3D structure, such as sponges, the electroconductivity is poorly containable because the 3D structure, as a spatial mask, decreases the uniformity and continuity of the deposited metal films initiated by gravity. [18] Recently, Liu et al. reported the polymer-assisted metal deposition by surface-initiated atomic transfer radical polymerization. [19] The designed polymer interface introduces covalent bonds between the surface of fibers and grafted polymer brushes and viscoelastic and high-swelling intrinsic properties of polymers provide the nanometer-scale mechanical interlocking of deposited nanoparticles within brushes. Although the resultant conductive yarns are highly durable and washable, the polymerization requires an inert N 2 protection and complex steps. Moreover, the target substrates have to contain abundant hydroxyl groups. On the other hand, with the booming development of novel materials, which can be employed in wearable electronics as their variety of performances, how to develop a new surface modification method which can be used in virtually any substrate and create conductive composites is important.According to Lee's report, [20] dopamine which mimics the adhesive chemistry of mussel plaque detachment allows the spontaneous deposition of nanoscale-thin, surface-adherent films of poly(dopamine) (PDA) on virtually all material surfaces such as polymers, ceramics, semiconductors, and novel metals by simple dip-coating in an alkaline solution. More importantly, secondary reactions can be used to produce a variety of ad-layers on the top of PDA, including metal films by electroless metallization. [21] In some reports, silver (Ag) was coated on different fibers, such as polyester polyethylene terephthalate (PET), meta-aramid, glass, cotton, and polyurethane, via PDA-assisted electroless deposition (ELD). [22][23][24][25][26] However, in accordance with Zheng's review work, [27] silver, as a conductive coating material, is much more expensive than copper and nickel. More importantly, according to the European Commission and its nonfood Scientific Committee on Emerging and Newly Identified Health Risks, there are still some arguments related to the toxicity of silver nanoparticles and additional adverse effects caused by the use of silver nanoparticles should be further evaluated.To address the challenges, we report here a simple, versatile, and scalable approach for preparing highly durable, washable, and electrically conductive fibers and yarns by electroless nickel (Ni) plating on fiber surfaces modified with PDA as adhesive layers. Copper (Cu) can be an alternative coating choice due to the high conductivity and low price. However, the Here a bioinspired facile and versatile method is reported for fabricating highly durable, washable, and electrically conductive fibers and yarns. Self-polymerized dopamine plays as adherent layers for substrates and then captures Pd 2+ catalyst for subsequent metal deposition on substrates. The Pd 2+ ions are chelated and partially reduced to nanoparticl...