Synthesis and characterization of silicones containing cyanopropyl groups and their use in dielectric elastomer actuators

Polydimethylsiloxanes (PDMS) have recently been used as dielectric elastomer materials in electromechanical actuators. When they are soft enough, electric fields can change their shape. However, due to their low dielectric permittivity, large electric fields are required to induce a change. The approach presented here is to chemically modify silicones with cyanopropyl groups in order to increase their permittivity. Samples containing repeat units with cyanopropyl groups from 3 to 23% were synthesized, different methods being employed. The prepared polymers were cross-linked into thin films. The dielectric permittivity of these films increased from 2.4 (for the silicone matrix) to 6.5 for a film containing about 23% of cyanopropyl repeat units. The most promising materials were further optimized to meet the requirements for actuators and their electromechanical properties were investigated. Material A for example, which is a blend of PDMS and cyanopropyl-modified silicone, has a permittivity of 3.5 and higher moduli of elasticity as compared to the matrix but nevertheless shows 10% actuation strain at 40 V mu m(-1) which is a factor of 3.8 larger as compared to the matrix (2.6% actuation strain at the same voltage).