Controlling microdroplet formation by light

A surface with photocontrollable wetting behavior is introduced. A monolayer of a polymeric material containing 4'-[trifluormethoxy-4,4'-dibenzoazo] dyes in the side chains has been transferred on quartz slides and silicon wafer. The azobenzene chromophore possesses two distinct isomers, cis and trans. Transition between these states can be triggered by illumination with light of two different wavelengths. it will be demonstrated that with the use of light and a mask, fine cis-trans patterns on the order of micrometers can be written in the monolayer. The corresponding interface exhibits different wetting behavior. This is visualized by a surface decoration with water droplets. The formation of water microdroplets on the patterned monolayer can be controlled by light. Writing and erasing of patterns is completely reversible. The system has potential for studying wetting behavior on microstructured surfaces.