Mixing Molar Volume of Liquid n- and i-Alkanes Based on the Law of Corresponding States with Potential between Functional Groups

Abstract

The excess Helmholtz free energy of a liquid alkane mixture is expanded around that of a reference liquid, the pair potential of which is the sum of a hard-sphere potential and an attractive potential, with the difference between the potentials. The characteristic length of the mixture is chosen such that the first-order perturbation term vanishes. The molar volume of the mixture reduced by the characteristic length is expressed by the sum of those of the reference and the second-order perturbation term in the corresponding states. The equation of the mixing molar volume is expressed by the corresponding states equations of the mixture and the pure components with the characteristic length and energy without any binary interaction parameters and reproduces the observed mixing molar volume well. The characteristic parameters are expressed by the parameters of the potential between the functional groups in the molecules, which are not fluid specific.