Hybrid Metallic Foam with Superior Elasticity, High Electrical Conductivity, and Pressure Sensitivity

Growing interest has been received in metallic foams for their combined features of metals and porous structures. Coating metals on polymers have been the most prevalent method to fabricate hybrid metallic foams to inherit both the merits of metals and the mechanical flexibility of polymers. However, direct coating metals on foams is challenging and requires tedious synthesis, such as electrolysis and chemical reduction. This work reported a facile strategy to build hybrid metallic foams via in situ foaming of liquid metals (LM) and polyurethane. The fluidity and incompatibility of LM with porous polyurethane allow the coating of LM on polymers. LM-Foams exhibit high electrical conductivity (3.9 × 10⁴ S/m), low density (ρ < 1 g/cm³), phenomenal elasticity (recover at 95% strain), and excellent mechanical stability (stable with 1000 compressive cycles). Interestingly, the ease of deformation for fluidic fillers in elastic polyurethane generates additional resistive change under pressure, showing unique sensory behaviors which were not observed in conventional conductive foams, such as high response sensitivity (gauge factor >25), short response time (202 ms), and outstanding electrical stability. The nonuniform size distribution of pores leads LM-Foams to show unusual position-dependent sensitivity, enabling advanced applications as password pads and electrical protection foams.