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Land subsidence has threatened the safety of municipal infrastructures and even that of inhabitants. As one of the deformation monitoring methods, distributed optical fibre sensing (DOFS) technology has been developed for the investigation of land subsidence. The deformation coordination between the optical fibre and soil (DCf-s) under different conditions is critical for land subsidence monitoring with DOFS. In this paper, a medium-sized triaxial apparatus was modified for testing the DCf-s. Consolidated drained triaxial tests were conducted to investigate the effect of sand types on the DCf-s. By linearly fitting the deformation of the sensing cable with that of the triaxial specimen, the other factors that affect the DCf-s, such as the confining pressure, dry or wet state of the soil and cyclic variation of the loads, can be discussed. The experiments reveal that better DCf-s comes with a larger particle size, poor gradation of sand and larger confining pressure. The DCf-s of wet sand is better than that of dry sand. The DCf-s coefficient tends to be stable with an increase of loading cycles. The DCf-s obtained and its dependence on influencing factors can be used to modify the measured cable strain in practical land subsidence monitoring with DOFS. [ABSTRACT FROM AUTHOR]

Hydrogels are ideal materials for flexible electronic devices based on their smooth ion channels and considerable mechanical flexibility. A substantial volume of aqueous solution is required to enable the smooth flow of ions, resulting in the agony of low‐temperature freezing; besides, long‐term exposure to bending/tensile tress triggers fatigue issues. Therefore, it is a great challenge to prepare hydrogels with both freeze‐resistance and long‐term durability. Herein, a polyacrylic acid‐based hydrogel with both hydrophobic interaction and dynamic reversible covalent bonding cross‐linking networks is preparing (DC‐hydrogel) by polymerizing a bi‐functional imidazole‐type ionic liquid monomer with integrated disulfide and alkene bonds (DS/DB‐IL) and an octadecyl methacrylate, achieving self‐healing. The DS/DB‐IL anchored into the polymer backbone has a high affinity with water, reducing the freezing point of water, while the DS/DB‐IL with free ions provides superior ionic conductivity to the DC‐hydrogel. The polyacrylic acid with abundant carboxyl gives hydrogel good self‐adhesiveness to different substrates. Ionotronics with resistance‐type sensors with stable output performance are fabricated and explored its application to joint motion and health information. Moreover, hydrogel‐based sensing arrays with high resolution and accuracy are fabricated to identify 2D distribution of stress. The hydrogels have great promise for various ionotronics in many fields. [ABSTRACT FROM AUTHOR]

The emergence of novel e-textile materials that combine the inherent qualities of the textile substrate (lightweight, soft, breathable, durable, etc.) with the functionality of micro/nano-electronic materials (conductive, dielectric, sensing, etc.) has resulted in a trend toward miniaturization, integration, and intelligence in new electronic devices. However, the formation of a conductive network by micro/nano-conductive materials on textiles necessitates high-temperature sintering, which inevitably causes substrate aging and component damage. Herein, a bis-hydroxy-imidazolium chloride salt as a hard segment to synthesize a waterborne polyurethane (WPU) adhesive is designed and prepared. When used in nano-silver-based printing coatings, it offers strong adherence for coatings, reaching 16 N cm−1; on the other hand, the introduction of chloride ions enables low-temperature (60 °C) chemical sintering to address the challenge of secondary treatment and high-temperature sintering (>150 °C). Printed into flexible circuits, the resistivity can be controlled by the content of imidazolium salts anchored in the molecular chain of the WPU from a maximum resistivity of 3.1 × 107 down to 5.8 × 10−5 Ω m, and it can conduct a Bluetooth-type finger pulse detector with such low resistivity. As a flexible circuit, it also offers high stability against washing and adhesion, which the resistivity only reduces less than 20% after washing 10 times and adhesion. Owing to the adjustability of the resistivity, we fabricated an all-textile flexible pressure sensor that accurately differentiates different external pressures (min. 10 g, ~29 Pa), recognizes forms, and detects joint motions (finger bending and wrist flexion). [ABSTRACT FROM AUTHOR]

Presently, it is necessary to develop fully flexible sensors for the next generation of wearable electronics, and in this case, hydrogel-based flexible sensors are highly attractive due to their unique mechanical performances. However, the low-temperature freezing and bending fatigue of hydrogels severely hinder their application in flexible sensors. Herein, a polymeric dual-function hydrogel (DF-hydrogel) integrating self-healing and anti-freezing properties was prepared by building a dual dynamic network for application as ionic skin with excellent and reliable sensing performances. In DF-hydrogel, ethylene glycol (EG) and disulfide bonds were anchored in the molecular structure of double-bond-capped water-based polyurethane crosslinkers (DB-waPU) and subsequently introduced into the molecular backbone of the hydrogel via free radical polymerization. A multi-hydrogen bonding network was formed by the copolymerization of acrylamide with 2-ureido-4[1H]-pyrimidinone (UPy)-functionalized 1-vinylimidazole ionic liquid. Due to the dual dynamic network, DF-hydrogel exhibited exceptional self-healing capabilities and mechanical properties such as high healing efficiency, stretchability, compressibility, and self-adhesion. The anchored EG molecule in the polymer backbone endowed the hydrogel with intrinsic freeze-resistance without compromising its mechanical properties. The introduced poly(ionic liquid) provided free ions to the hydrogel, enhancing its ionic conductivity up to 9.6 mS cm−1 in the absence of applied electrolyte salts. The DF-hydrogel-based ionic skins exhibited rapid, reversible, and dependable resistance changes with a wide range of strain sensing capabilities (10–300%). Moreover, a prototype 2D sensor array was fabricated to detect strains or pressures in two dimensions, strongly showing potential for the preparation of electronic skin, touch-pads, biosensors, and other applications. [ABSTRACT FROM AUTHOR]