Electrohydrodynamic instability: effect of rheological characteristics on the morphological evolution of liquid crystal–polymer interface

Electrohydrodynamic instability, in a polymer–air or polymer–polymer bilayer settings, gives rise to the formation of the ordered micropillars or microwells at the initial planar interface. It is well known that the complex interplay among the controlling parameters, such as the intensity of the electrostatic field, film thickness, interfacial tension and dielectric constants of the layers determine the morphology of the interface. In this report, for the first time, experimentally it is shown that rheological property of the lower polymer layer [here, polydimethylsiloxane (PDMS)] has a significant influence on the morphological evolution. We probe the kinetic time scale of the evolution by inducing fast destabilization of the interface due to the high dielectric contrast between two layers (liquid crystal–PDMS) and reduced interfacial tension. At this time scale, it was demonstrated that micropillars are formed for thin viscoelastic ‘soft’ PDMS film, whereas microwells were observed for viscoelastic ‘hard’ film in similar settings. A transition from micropillar to microwell was observed for viscoelastic ‘soft’ film when the thickness of the film increased from $${\sim } 4$$ to $$11\,\upmu \hbox {m}$$ . Based on this observation, by controlling the rheological properties, different patterns were developed from similar templated PDMS substrates.