Transient Electrically Driven Stiffness-Changing Materials from Liquid Metal Polymer Composites

Stiffness-changing materials (SCMs) have received lots of interests due to their reversible transition between their soft and rigid states for modern applications. However, the irreversible stiffness transition, slow response, and sustained external stimuli strictly hinder the broad utilizations of SCMs. Here, this work reports electrically driven SCMs based on supercooled liquid metals (LMs). A small voltage (5 V) can successfully initiate the stable and reversible stiffness change of the SCMs in electrolyte solution. Surprisingly, the LM-based SCMs (LM-SCMs) exhibited a significant change in 1000 times difference of moduli (65 kPa versus 79 MPa). Moreover, such a stiffness transition of the LMSCM was ultrarapidly completed in a few seconds (<30 s). Importantly, after transient stimulation of LM nucleation, the rigidity of the LM-SCM could be maintained when the external stimulus (voltage) was removed, highly different from previously reported SCMs that require sustained energy to maintain their mechanical states. Based on the unique features of LM-SCMs, advanced robotics like smart valves and mechanical paws in seawater were successfully fabricated.

Automated summary

This study reports electrically driven stiffness-changing materials based on supercooled liquid metals, which can achieve stable and reversible stiffness change with significant modulus differences, and complete the hardness transition within seconds. Unlike previously reported materials, this material can maintain rigidity after the stimulus is removed.