Exploring the complex deformation behavior of liquid metal polymer composites through experimental and novel computational approaches

Unique among traditional fillers, the metallically conductive liquid metal galinstan has emerged as an inherently deformable alternative for polymer composites. Galinstan exhibits high electrical conductivity with liquid-like flow, which sets it apart from the solid metals and ceramics typically used to impart electrical behavior to polymers. Upon exposure to atmospheric oxygen, galinstan forms a solid oxide shell that adds mechanical complexity when blended with polymers to create liquid metal polymer composites (LMPCs). This study investigates the mechanical behavior of LMPCs under tension, compression, and torsion as a function of LM droplet size and loading. Experimental analysis and computational modeling reveal distinct behaviors in LMPCs depending on the applied force and droplet characteristics that do not follow the classic composite models like Eshelby theory or more recent, updated versions thereof. Despite the large modulus difference between the LM and oxide shell, focusing exclusively on individual droplet mechanics overlooks the importance of surface energy dynamics within the system. By incorporating interfacial energy into a novel model, the origins of the LMPC mechanical response under deformation were illustrated. Our findings contribute to a broader understanding of composite materials with implications for soft robotics, where material response to various deformations is crucial for functionality.