Electronic modulation of an electrochemically induced wettability gradient to control water movement on a polyaniline surface

Wettability gradients can be electronically controlled in a multiple-electrode electrochemical structure that consists of a solid electrolyte and the conducting polymer polyaniline doped with dodecylbenzenesulfonic acid as the active surface. A bias applied directly between a counter electrode and the surface to be switched determines the initial water contact angle, while the potential between two electrodes on either side of the switch surface, connected to each other and the switch surface only through an electrolyte, induces a surface energy gradient. The spreading of water on the switchable surface can be modulated with both potentials. The wettability at each point of the switch surface is correlated to the local electrochromic state (visible color) of the material, offering a visual indication of how a water drop will spread before it is applied. This new device has potential applications in scientific areas such as micro-fluidics and biomaterials. (c) 2006 Elsevier B.V. All rights reserved.