Flexible enhanced energy density composites for dielectric elastomer actuators

Dielectric elastomer actuators deform due to voltage-induced Maxwell-stress, which interacts with the mechanical properties of the material. Such actuators are considered for many potential applications where high actuation strain and moderate energy density comparable to biological muscle are required. However, the high voltage commonly required to drive them is a limitation, especially for biomedical applications. The high driving voltage can be lowered by developing materials with increased permittivity, while leaving the mechanical properties unaffected. Here, an approach to lowering the driving voltage is presented, which relies on a grafted nano-composite, in which conducting nanoparticles are integrated directly into a flexible matrix by chemical grafting. The conducting particles are π-conjugated soft macromolecules, which are grafted chemically to a polymer matrix flexible backbone. Dielectric spectroscopy, tensile mechanical analysis, and electrical breakdown strength tests were performed to fully characterize the electro-mechanical properties. Planar actuators were prepared from the resulting composites and actuation properties were tested in two different modes: constant force and constant strain. With this approach, it was found that the mechanical properties of the composites were mostly unaffected by the amount of nanoparticles, while the permittivity was seen to increase from 2.0 to 15, before percolation made further concentration increases impossible. Hence, it could be demonstrated that the socalled "optimum load" was independent from the permittivity (as expected), while the operating voltage could be lowered, or higher strains could be observed at the same voltage.