Dielectric elastomers can be actuated under electric field responding to electrostatic force. Compared with other electrical actuation technologies, the advantages of dielectric elastomer actuators include: light weight, good compliancy, large actuation strain, high energy density, quiet operation and low cost. As the active part of an actuator device, the dielectric elastomer material plays a central role. However, most popular elastomers used for dielectric actuation are commercial products designed for other applications. And their confidential formulations also make it difficult to understand the mechanism and further improve the actuation performances. Therefore, the development of new dielectric elastomers from molecular level is of great importance.
One subject in this dissertation is the synthesis of a group new dielectric elastomers from molecular level which demonstrate high actuation strains. These dielectric elastomers are polyacrylate formulations with n-butyl acrylates as the based monomer and formed through ultra-violet polymerization. The influences of acrylic acid in the formulation on the mechanical and dielectric properties are investigated. The optimal formulation demonstrates an area actuation strain of 186 %, a dielectric strength of 222 MV/m and an energy density as high as 1.4 MJ/m3.
As the dielectric constant of a dielectric elastomer plays a significant role in its actuation performances, one focus of this dissertation is to improve the dielectric constant by utilizing nanocomposites. Aluminum nanoparticles with a self-passivated oxide shell are used as the conductive fillers to increase the dielectric constant of a polyacrylate elastomer while retaining a high dielectric strength. With the addition of 4 vol% Al nanoparticles, the nanocomposite has a dielectric constant as high as 8.4 with a maximum actuation strain of 56 %, a dielectric strength of 140 MV/m and a maximum actuation pressure of 1.5 MPa.
Another focus of this dissertation is the innovation of a dielectric elastomer with tunable stiffness. This novel elastomer contains furan-maleimide Diels-Alder adduct moieties as the dynamic bonding. The moduli of these elastomers can be tuned reversibly and incrementally through modulating their crosslinking densities via thermal treatments at moderate temperatures. Capacitive sensors and actuators which can work in multiple modes were fabricated using the new materials.