Volume fractions are used in our calculations for Gibbs Free Energy Change of Mixing, Enthalpy Change of Mixing and Entropy Change of Mixing.
A polymer length is divided into segments, such that a segment has the same volume as a molecule of the solvent. In the above model, with 24 solvent molecules, there are three polymer chains. Two polymer chains have 8 segments, and the third chain has 9 segments, for a total of 25 segments.
Volume fractions vary between 0 and 1.The math: 24/49 = 0.49 and 25/49 = 0.51
Volume fractions follow the convention that the subscript 1 refers to solvent and the subscript 2 refers to polymer. Thus, v1=0.49 and v2=0.51.
