Partial Wetting Phenomena on Nonplanar Surfaces and in Shaped Microchannels

Abstract

Surface tension and wettability are important phenomena in many diverse areas of science and technology, such as adhesion, adsorption, lubrication, catalysis, solid−liquid reaction kinetics, and microelectromechanical systems. However, when the solid surface is not perfectly planar, liquid contact with that surface is poorly understood and the subject of considerable misconception. Here, we report that under static or near-static conditions wettability is dependent not only upon the contact angle between the liquid and the solid but also on the geometry of the surface that the liquid contacts. It is shown that the artificial dividing line of 90° between wetting and nonwetting behavior only holds on a planar surface or in a straight channel. The conditions controlling whether filling of an interstice takes place or not are demonstrated to be a function of both the liquid−solid contact angle and the included angle within the interstice. This behavior is both reversible and reproducible. A simple relationship is developed to express the transitional included angle of the interstice as a function of contact angle.