Studies of Electric-Field Induced Surface Instabilities using Confocal Microscopy

Abstract

Dielectric elastomer actuators (DEAs) are electro-mechanical transducers that can convert an electrical input into mechanical work. They have found many applications including soft robotics and tunable windows. The latter operate by applying an electric potential to the DEA, inducing surface morphological changes that scatter light and reduce in-line transmittance. Tunable windows operate in two regimes of behavior. In the low electric field regime, inhomogeneous surface deformations of the elastomer form, which cause local variations in optical refraction and changes light transmittance. In the high electric field regime, an array of pits forms on the surface by a nucleation and growth mechanism. The pits also scatter light. Much of the theoretical understanding of the aforementioned instability and growth mechanism has arisen from scaling arguments and perturbation analysis, built upon experimental investigations of the surface instabilities. While most prior studies have focused on only the superficial features of the instabilities, minimal effort has been devoted to imaging their shape at higher fields, much larger the initial surface instability. My thesis describes observations, using fluorescence confocal microscopy, of the three-dimensional shape evolution in the post-instability regime, as the applied voltage is increased. These reveal a complex series of previously unknown, and reversible, geometric instabilities. I also performed a scaling analysis showing that the energetics of the system are dominated by the electrostatic and elastic energies with minimal surface energy contributions. Finally, I investigated the electromechanical behavior of the fundamental building block of tunable windows, which is the deformation associated with charging a single wire on the surface of a dielectric elastomer. I imaged the surface and volumetric deformations induced by the wire as it was actuated by an increasing potential difference. This serves as a starting point for further theoretical and experimental investigations of the interactions between multiple, percolating wire electrodes.