The energetics of magnetoelastic actuators is analogous to phase transformations in materials

A ferrogel is a composite system comprised of a polymeric matrix and magnetic filler particles. The elastic properties of the polymer can be coupled with the magnetic properties of the particles to create novel soft actuators. Understanding the mechanical behavior of ferrogels in an external magnetic field is essential to optimize actuator performance. The energetics of the mechanical behavior of cylindrical ferrogel specimens was found to be analogous to the energetics of chemical phase transformations in materials. Depending on the sample geometry, the elongation mechanism of ferrogel cylinders in an external magnetic field was identified as either a continuous or discontinuous deformation, analogous to a second- or first-order phase transformation, respectively. In analyzing mechanical strain as a function of magnetic field, the first and second derivatives of energy can be used to predict metastability and transitions in ferrogel deformation behavior.