11: Review of Dielectric Elastomers (DEs) as Smart Materials

Chapter 11 reviews dielectric elastomers (DEs). If rubbery elastomers like a silicone rubber sheet are sandwiched between two compliant electrodes, then any imposed electric field induces electrostatic forces (attraction) between the electrodes. Thus, the rubber sheet in between them can be compressed by the electrostatic forces, which then cause the rubbery sheet to expand sideways due to the Poisson's ratio effect and thus, actuation results. In 1880, Röntgen demonstrated this actuation by using two glasses as dielectrics, and once the opposing surfaces of these glasses were charged, small thickness changes were observed by Röntgen. Later electrostatically-induced pressures acting to compress dielectrics became known as the “Maxwell stress.” It was, however, Perline, Kornbluh, and Joseph in 1998 who introduced dielectric elastomer technology with compliant electrodes. They concluded that by deliberately choosing polymers with relatively low moduli of elasticity, the field-induced strain response due to Maxwell stress could be large. Polymer actuators designed to exploit Maxwell stress in this manner, became known as dielectric elastomers or DEs.