Indentation and temperature response of liquid metal/hydrogel composites

Abstract

The volume transition of thermo-responsive hydrogels has been investigated for various applications such as soft actuators, sensors, drug delivery systems, and bioelectronics. Nonetheless, issues such as poor mechanical properties, slow transition rates, and limited volume change windows have prompted the development of hydrogel composites. Gallium (Ga), a liquid metal, is combined with poly(N-isopropyl acrylamide) (PNIPAm) with varying composite structures in this work. Ga's melting point is close to PNIPAm's volume transition temperature. The introduction of Ga particles into PNIPAm improves both the indentation resistance and the transition rate of the hydrogel. Microchannel structure can further improve the transition rate by increasing the water diffusion rate. The relatively fast thermal conduction of the Ga phase in anisotropic composites causes fast deswelling of Ga-rich regions, resulting in unique double bending behavior. The double bending behavior was utilized to hold irregularly shaped objects firmly. These results offer a useful design strategy of composites for the development of novel responsive smart systems.