Combined Light and Electric Response of Topographic Liquid Crystal Network Surfaces

Abstract

An approach is proposed to create robust liquid crystalline polymer coatings that exhibit sensitivity and dynamic reversibility toward multiple external stimuli including UV irradiation and electrical input. This coating spontaneously alters its surface topographic texture and thickness in response to each of these signals. The corresponding deformations are induced by the photo-/electromechanical properties and dielectric anisotropy in the liquid crystal networks through order parameter reduction and anisotropic volume expansions. The deformation proceeds fast within several seconds both for activation and for the relaxation to the initial state upon switching the trigger(s) on and off. Light and electric field can be applied independently to excite the topographies or in a synergistic manner to enhance the deformation amplitude. Upon elimination of the combined light and electric actuating trigger, the relaxation to the initial close to flat state follows a complex pathway. Depending on the elimination order the topographic structure can be rapidly erased or can be kept in a bistable state. The results of this study are relevant for various fields, for instance, switchable controlled friction, controlled adhesion, and release of objects and haptics where they affect human perception both in passive and dynamic manner.