Electro-creasing Instability in Deformed Polymers
Subjected to an electric field, a substrate-bonded polymer film develops a biaxial compressive stress parallel to the film. Once the electric field reaches a critical value, the initially flat surface of the polymer locally folds against itself to form a pattern of creases. As the electric field further rises, the creases increase in size and decrease in density, and strikingly evolve into holes in the polymer. We show that mechanical deformation of the polymer significantly affects the electro-creasing instability. Biaxially pre-stretching the polymer film before bonding to the substrate greatly increases the critical field for the instability, because the pre-stretch gives a biaxial tensile stress that counteracts the electric-field-induced compressive stress. We develop a theoretical model to predict the critical field by comparing the potential energy of the film at flat and creased states. The theoretical prediction matches consistently with the experimental results. The theory also explains why biaxially pre-stretching a dielectric-elastomer film greatly enhances the measured breakdown field of the film.
I am the first year Ph.D. student of Mechanical Engineering and Material Science at Duke University. Before coming to Duke, I held my B.S. degree in Theoretical and Applied Mechanics at Fudan University in Shanghai, China. In my junior year at Fudan, I joined Advanced Materials and Mechanics Lab, working on dispersion fuel element with finite element method. During that research, I published four international papers and a conference paper. I found myself so interested in mechanics of advanced materials, so I decided to attend Duke University to work with Prof. Xuanhe Zhao in studying mechanics of soft materials. My recent research basically is focused on the Ceasing to Holing instability of soft polymers under ultrahigh voltages. Our research not only is a fundamental topic in physics of soft matter, but also has broad applications including insulating cables, polymer capacitors, surface patternings, polymer actuators, semi-permeable membranes and bio-lipid bilayers.