Liquid metals in plastics for super-toughness and high-performance force sensors

Electrically conductive and mechanically stretchable materials based on liquid metal-embedded elastomer compositions have been widely studied for stretchable sensors. However, liquid metal (LM) in plastics possessing outstanding mechanical properties have not been reported. Here, we fabricated a super-tough force sensor based on liquid metal-polyvinyl alcohol composites (LM-PVA) which exhibited unique sandwich structure with conductive LM composites between two insulated layers. Uniform dispersion of LM in PVA matrix was achieved due to the high viscosity of PVA solution and the surface interaction of PVA and oxide layer of LM. Besides, soft LM droplets remarkably toughened the PVA plastics with 12.3 times increase in toughness (74 vs 6 MJ/m3). The solvent-processed LM-PVA films showed phenomenal mechanical durability (>1000 cycles of stretching and compressing). Flexible resistance and capacitance sensors can be conveniently constructed to detect daily motions, such as stretching, finger bending and bicycle rolling, owing to its unique electrical sensitivity and mechanical durability. Compared with LM-elastomer sensors, LM-PVA showed excellent abrasive resistance and high temperature resistance. This work highlights the potential of LM-plastics in broad applications and can facilitate the realization of flexible sensing devices under engineering applications.