Liquid crystal elastomer coatings with programmed response of surface profile

Stimuli-responsive liquid crystal elastomers (LCEs) with a strong coupling of orientational molecular order and rubber-like elasticity show a great potential as working elements in soft robotics, sensing, transport and propulsion systems. In this work, we demonstrate that the predesigned director patterns can be used to control a dynamic surface topography of LCE coatings. The director pattern is created by a photoalignment method. As the temperature changes, the coating responds by changing the topography of the free surface. The topography change is uniquely determined by the director pattern preprogrammed during the alignment and polymerization of LCEs. The deterministic dependence of the dynamic surface profile on the director pattern is explained by activation forces rooted in (i) stretching-contraction of the polymer networks driven by temperature; (ii) spatially varying orientation of the LCE. The activation force concept brings the responsive LCEs into the domain of active matter. The demonstrated relationship can be used to design programmable coatings with functionalities that mimic biological tissues such as skin.