Mechanical characterization of granular actuators

Phase-change granular actuators combine the high volumetric expansion and actuation stress of bulk phase-change systems with the tunable properties of granular materials. One form of these actuators utilizes microcapsule grains made from an elastic matrix encapsulating multiple solvent cores, where phase changes from liquid to gas drive volumetric expansion. Previous work demonstrated grain expansions up to 700%, though material selection was not optimized. This study explores how shell and core material choices affect the synthesis and performance of phase-change granular actuators. We identify specific combinations of solvents and silicone matrices that influence encapsulation efficiency, grain morphology, and processing requirements. Results show that increasing shell stiffness and core solvent boiling point raises actuation temperatures, while softer shells enable greater volumetric expansions. Overall, tuning the material composition allows for control of actuation metrics.