Novel coiling behavior in magnet-polymer composites

Magnet-polymer (Magpol) composites have an interesting ability to undergo large strains in response to an external magnetic field. The contraction behavior of composites of silicone and micron sized iron particles induced by an external magnetic field was studied. Simply by changing boundary conditions, Magpol can exhibit shape change from axial contraction to a novel coiling mechanism due to buckling. The analytically predicted magnetic fields for buckling agreed well with the measured values. The strain versus magnetic field relationship suggested that postbuckling behavior is a stable symmetric bifurcation, which is useful for continuous actuation. The coiling mode of Magpol exhibited high actuation strain (up to 60%) and actuation stress (up to 184 kPa), thus shows good potential for use in soft actuators.