Electrowetting Phenomenon on Nanostructured Surfaces Studied by Using Atomic Force Microscopy

Abstract

An electrowetting (EW) phenomenon was studied using atomic force microscopy (AFM) on poly(methyl methacrylate) (PMMA) surfaces with nanostructures formed by lithography treatment or covered with a thin layer of titanium dioxide (TiO2) nanoparticles. By measuring the adhesion force, as well as its magnitude of fluctuations, between the conductive AFM tip and the dielectric surface at different electric fields, the characteristic EW features could be identified. By comparison of the EW characteristics on smooth PMMA surface with that on a lithographically patterned or TiO2-nanoparticle covered PMMA surface, the impact of the three-phase contact line and dielectric properties on the EW phenomena could be demonstrated. It reveals that the transition from ideal EW to EW saturation is associated with intrinsic dielectric properties rather than with the solid–liquid interface characteristics. The second transition from EW saturation to EW breakdown could be attributed to changes in the three-phase contact line.