Structure and Forces in Liquids and Liquid Mixtures

Abstract

In this chapter, we shall discuss first the statistical mechanical theory of liquids(1), and then of liquid mixtures. The discussion will include the theory of freezing of some simple liquids. This is closely related to the theory of the bulk liquid structure, the main topic of the first part of this chapter. Here, the so-called Born—Green—Yvon hierarchy is the starting point of all structural theories of simple liquids. This hierarchy was also used in the pioneering studies of Kirkwood and his school(2) on the theory of freezing. Modern trends in the theory of both liquid structure and freezing have emphasized the Ornstein—Zernike direct correlation function c (r), which is more directly connected with the interparticle interaction than the liquid pair function g(r), to be defined precisely below. This function c (r) [see equation (3.4.2) below] will therefore be a focal point in this discussion. However, first we shall give an operational definition of the structure factor S(k) of a simple liquid like argon, by summarizing the results for the intensity of X-ray scattering (see Chapter 1 for full details of the diffraction experiments).