Surface free energy of solids and liquids: Thermodynamics, molecular forces, and structure

Abstract

Surface chemistry constitutes a major part of science which has ubiquitous consequences in chemical processes, in engineering and technology, in biology and medicine, and, indeed, in the very existence of life. There are two properties of surfaces that are fundamentally responsible for these consequences. One is surface free energy; the other is surface charge. We owe the concepts of surface tension and surface free energy to several of the great physicists of the 19th century, such as Young (1) and Gibbs (2). Gibbs worked out the basic surface thermodynamic concepts a century ago; this was several decades before even the order of magnitude of the dimensions of molecules was established, and long before polymers were given scientific recognition. I t has been a major item on the agenda of physical science for over a century, to find out how the experimental, macroscopically observable quantities, such as surface tension, are related to atomic and molecular structure. A number of important chemists and physicists worked on this agenda, before and shortly after Word War II. I will review several aspects of this earlier work, in order to show what it was that made it possible for my research group at Cincinnati, 20 years ago,