Thermodynamics of mixing

Abstract Mixtures are systems consisting of two or more different chemical species. Binary mixtures consist of only two different species. An example of a binary mixture is a blend of polystyrene and polybutadiene. Mixtures with three components are called ternary. An example of a ternary mixture is a solution of polystyrene and polybutadiene in toluene. If the mixture is uniform and all components of the mixture are intermixed on a molecular scale, the mixture is called homogeneous. An example of a homogeneous mixture is a polymer solution in a good solvent. If the mixture consists of several different phases (regions with different compositions), it is called heterogeneous. An example of a heterogeneous mixture is that of oil and water. Whether an equilibrium state of a given mixture is homogeneous or heterogeneous is determined by the composition dependence of the entropy and energy changes on mixing. Entropy always favours mixing, but energetic interactions between species can either promote or inhibit mixing.