The Interfacial Physics Group

Carnegie Mellon University, Department of Physics

Interface Shapes and Thin Film Structures of Complete, Partial, and Pseudo Partial Wetting Systems
by Keith Daniel Humfeld



Traditionally, systems are said to exhibit one of three wetting conditions: complete wetting, where the contact angle of the capillary body is zero; partial wetting, where the contact angle is nonzero and the there is no fluid on the substrate beyond the macroscopic contact line; and pseudo-partial wetting, where the contact angle is nonzero, but there is a film in equilibrium with the capillary body. Using energy minimization and a force balance formulation, these wetting states are re-examined and the differences between them are elucidated in detail. The conditions leading to complete, partial, and pseudo-partial wetting in various geometry are determined. Moving beyond previous discussion, we clearly differentiate between partial wetting which can have a “foot” at the contact line and pseudo-partial wetting. We contrast the phenomenon of autophobing, in which a fluid has a nonzero contact angle on top of its own monolayer, with pseudo-partial wetting. Complete wetting and pseudo-partial wetting are examined in cases where the film terminates on the substrates and cases where the film is infinite in extent. Infinite substrates and systems where the end of the substrate is important in determining the wetting state are considered. Further, evidence that a single material system can exhibit complete wetting in one geometry and pseudo-partial wetting in another geometry is shown, demonstrating that such transitions in wetting behavior occur when the size of the system changes. This re-examination of wetting produces a complete and unified picture of the classic states of wetting.