ABSTRACT
Understanding the physical chemistry of binary mixtures is important, as they constitute a wide and highly useful class of solvents in chemical and biological applications. In fact, in the real world, liquids and solvents are mostly mixtures of several components. When the two components of a binary mixture differ significantly in their individual chemical properties, we can tune the properties of the mixture to a great extent by changing the composition. One often observes a myriad range of behavior of a mixture as a function of composition. Properties of a binary mixture are often discussed in terms of deviations from Raoult’s law that defines an ideality of solution by the degree of adherence of a property P to the relation https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315113951/38b80d50-9b72-4816-a8b1-f0785f387cc6/content/inline-math26_1.tif"/> P = ∑ i x i p i , where x i is the mole fraction of the ith species. Composition dependence of certain properties, notably viscosity and excess volume of the solution, reveal interesting information about the structure of the mixture. When viscosity is larger than the ideal value (as predicted by Raoult’s law), the mixture is called a “structure making” mixture. In the reverse situation, it is called “structure breaking.” Statistical Mechanics attempts to provide explanation of such diverse behavior exhibited by binary mixtures in terms of six parameters, three interaction energy parameters and three size parameters. The simplest theory of binary mixture is given by Flory and Huggins. A more sophisticated one was developed by McMillan and Mayer. Interestingly, some properties of binary mixture can be explained by using the solutions of the Ising model because one system can be mapped into the other, as we describe below. At the end, however, we have to turn to the distribution function theory to obtain a quantitative description of binary mixtures. An interested reader is encouraged to go through References 1 and 2.
