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Piezoresistive pressure sensors based on conductive polyurethane (PU) sponge have attracted much attention due to their facile fabrication, convenient signal collection and good stability, yet it is a challenge to prepare a cost-effective PU composite for pressure sensing with good sensitivity and a wide strain range. Herein, a conductive poly(vinyl alcohol)/sulfuric gel electrolyte@PU (PVA/H2SO4@PU) composite is fabricated by impregnating commercial PU sponge into a PVA/H2SO4 gel electrolyte. The conductivity of the as-prepared composite is provided by the gel electrolyte and the carbonized PU sponge by sulfuric acid. Due to the typical porous structure of the elastic PU sponge and the high elasticity of the PVA/H2SO4 gel electrolyte, the composite shows excellent compression performance. The PVA/H2SO4@PU-based piezoresistive pressure sensor exhibits a good sensitivity of 0.080 kPa−1 in a tiny and low pressure range (0.51–3.01 kPa), a wide sensing range (0–80.0%) and a long durability over 1800 s (1325 cycles). Thereafter, the pressure sensor was used to monitor facial muscle movements, airflow, finger bending, grasping different amounts of weights, etc. This indicates that the pressure sensor obtained in this work has broad application prospects in human activity monitoring. Furthermore, the PVA/H2SO4 gel electrolyte is readily available and inexpensive, which reduces the cost of the composites for pressure sensing.

Conductive polymer composites (CPCs) are popular materials for strain sensors that can detect joint movements and monitor human health. However, it is still a challenge to balance the mechanical strength, resistance, wide function range and durability of CPCs. Herein, a textile-based CPCs, PFNS (polypyrrole/β-FeOOH modified nylon (containing 30% polyurethane)), has been prepared via in-situ hydrolysis of Fe3+ and in-situ polymerization of pyrrole. The stacked acicular β-FeOOH constructs more space for polypyrrole growth, rendering PFNS lower resistance (5 cm, 0.308 kΩ) and higher electrothermal temperature (50.4 °C at 12 V) than PNS (without β-FeOOH, 5 cm, 0.493 kΩ, 41.3 °C at 12 V). The rough polypyrrole layer endows PFNS with good hydrophobicity that can be still maintained under 100% strain and after electrothermal heating. The PFNS possesses outstanding one-dimensional stretchability (100% strain), fast response time (0.39–0.61 s) and recovery time (0.55–0.92 s) for the strains of 2.5%-10%, good sensitivity (3.24 MPa−1 in a high stress of 0.123 MPa and gauge factor of 3.06 in a 20% strain), and long-term sensing function (>1500 cycles). Furthermore, PFNS presents excellent detection capability for subtle, middle and large joint movements (e.g., pronouncing, back bending, push-up exercise, walking and jumping), indicating its flourishing prospect in wearable strain sensors.

Electrothermal heater (ETH) is very promising in wearable electronic area for its potential thermotherapy and electrical-warming garment applications. To fabricate a suitable conductive material for wearable ETH, knitted cotton is used as substrate for in-situ polymerization of pyrrole monomers, producing conductive polypyrrole/knitted cotton fabric (PKCF) with good flexibility and stretchability. A parallel strategy for current collectors is taken to enhance the temperatures of prepared PKCF from 37.0 to 51.0 °C at 8 V. This PKCF provides a service time about 13.5 h in a continuous electrothermal process, keeping a temperature above 35 °C. Besides, the PKCF still shows good electrothermal performances after bent or stretched several thousand times, and can be sewn on fabric to realize its electrothermal function in garments, which indicates a promising wearable market.

Thermal energy storage has attracted more and more attentions due mainly to its ability of peak load shifting. Shell-and-tube configuration is a typical heat exchanger for thermal energy storage. T ...