Dielectrowetting on curved surfaces

Abstract

Programmable fluidic systems on curved and flexible substrates are of increasing interest. One approach to achieving programmability is the controlled sequential wetting and dewetting on a surface using voltage actuation. In particular, liquid dielectrophoresis techniques have recently been shown to provide the ability to form a spread liquid film on a normally liquid repellent, but rigid, substrate via applying a spatially periodic electrical potential underneath an initial sessile droplet. In this work, we demonstrate the creation of thin, rectangular shaped, films of electrically insulating liquid on the side of a curved and flexible liquid repellant substrate using dielectrophoresis forces. We find that the experimental threshold voltage V T (κ s) for film formation has a monotonic dependence on the value of the substrate curvature κ s in the range -0.4 mm-1 < κ s < 0.26 mm-1. By considering the balance of stresses acting on the films, including the Laplace pressure and the Maxwell stress, we develop an analytical theoretical expression that is in excellent quantitative agreement with our curvature dependent experimental threshold voltage measurements. The resulting physical insights and the demonstration of programmable wettability on curved and flexible substrates with both positive and negative curvature provide the foundations for applications in imaging, displays, and biochemical analysis.