Liquids And Their Interfaces

Abstract

Abstract So far we have considered photons, electrons, phonons, and gas molecules. The transport processes of these energy carriers have many common characteristics and thus we have treated them in parallel. Transport in liquid is considerably more difficult to deal with. Compared to gases, liquids have molecules are closely packed and have short-range interactions, while compared to crystalline solids, liquids lack the periodicity of crystal structures. For these reasons, we cannot develop a parallel treatment for transport in liquids as we have done in previous chapters for other energy carriers. This chapter provides a brief description of transport processes in liquids and near the interfaces between liquids and their surrounding media, such as liquid-solid, liquid-liquid, and liquid-vapor interfaces. We will start with a brief introduction to the methods used to deal with transport in bulk liquids. Historically, some of the earliest approaches were attempts to modify kinetic theory, particularly the Boltzmann equation, to include, for example, the finite size of liquid molecules and the potential interaction among molecules. The success of modified kinetic theories, however, is rather limited. Another line of development was pioneered by Einstein (1905) in his studies of the Brownian motion of particles in a liquid. Brownian motion was generalized by Langevin, and further developed by others in the linear response theory (Kubo et al., 1998). With the development of computational tools, the study of liquids has gradually shifted to computer simulations based on the linear response theory. In section 9.1, we will discuss the modification of the Boltzmann equation by Enskog, Einstein’s Brownian motion theory, and the Langevin equation. The linear response theory will be discussed in chapter 10.