Electric-field induced instabilities and morphological phase transitions in soft elastic films

We investigate the morphological transitions of surface patterns induced in a soft elastic film in the presence of an applied electric field by the linear stability analysis and simulations. The surface patterns emerge beyond a critical strength of the electric field and the pattern length scale is always nearly three times the film thickness, regardless of the precise pattern morphology and other physical parameters. Interestingly, the simulations show that the precise pattern morphology depends strongly on the film and the field parameters and can be classified into three broad morphological phases: columns, stripes, and cavities. By tuning the electric field and the gap distance, we show that transitions from one morphological phase to another can be induced as described by a morphological phase diagram for this phenomenon. We also study the conditions under which the transitions can be "glassy" or "hysteretic." In addition to uncovering the rich physics underlying these nearly two-dimensional morphological phase transitions, our simulations also suggest experiments and applications of this phenomenon in mesopatterning. In particular, simulations demonstrate the possibility of controlling the pattern morphology and alignment by using the electric-field induced instability in soft elastic films. Unlike the short range adhesive interactions which cannot be varied, the use of an electric field allows far greater flexibility in modulation and control of the pattern morphology and its height.