The study of wetting, simply stated, is the study of the interactions between bulk phase transitions and surfaces. The central question of wetting physics is: “what will happen on a surface in the neighborhood of a phase transition in the bulk?” It is clear because of the variety of possible surfaces and bulk phase transitions, that wetting is an extremely rich and interesting basic physics problem. It is equally clear that since every real object has boundaries or surfaces, an understanding of wetting phenomena has many important technological applications. Problems ranging from the flow of oil through sand to the fabrication of semiconductor devices can be addressed through an understanding of wetting.
Over the last several years, liquid helium has become an important model system for the study of wetting [43]. In particular, studies of pure 4He adsorption on cesium resulted in the first measurements of the complete phase diagram associated with a first order wetting transition [4]. The experiment described here examines the wetting behavior of binary liquid mixtures of the two helium isotopes, 3He and 4He, on a cesium substrate near the bulk phase separation line. It provides the first direct observations of triple point dewetting transitions and reveals a connection between wetting, prewetting, and triple point dewetting transitions that should be a general feature of binary liquid wetting.
Most of the material contained in these pages is taken from the Ph.D. dissertation of David Ross completed in January 1996, at the University of California, Irvine.