Electro-creasing instability in deformed polymers: experiment and theory

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. 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.