A hydrophobic conductive strip with outstanding one-dimensional stretchability for wearable heater and strain sensor

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.