Electrospraying Nanometer-Thin Elastomer Films for Low-Voltage Dielectric Actuators

Micrometer-thin polymer films are often prepared using spin coating. In applications such as low-voltage dielectric elastomer actuators (DEAs), however, nanometer-thin polymer layers are required. In this paper, it is demonstrated that alternating current electrospray deposition allows for the fabrication of high-quality nanometer-thin polydimethylsiloxane (PDMS) films. The growth of the PDMS with an average molecular weight of 6000 g mol(-1) at rates of 0.02-5.54 nm s(-1) was in situ monitored by means of spectroscopic ellipsometry. The Cauchy layer model performs above a deposition-rate-dependent average film thickness, which is associated with a confluent film. The droplet size measurements as the function of deposition rate show that inertia and polarization forces dominate in liquid PDMS electrospraying. The roughness of the deposited films increases with the spray rate. After UV-light curing under Ar atmosphere, however, the films smoothen to root-mean-square roughness values between 0.20 and 0.28 nm determined by atomic force microscopy on areas of 5 mu m x 5 mu m and between 2 and 20 nm determined by interferometry on an area of 0.72 mm(2). Such electrosprayed PDMS films with (sub-)nanometer roughness qualify for the fabrication of low-voltage DEAs.