Cavity formation free energies for rigid chains in hard sphere fluids

Excluded-volume-anisotropy (EVA) model predictions for the cavity formation free energies of rigid linear polyatomic chains dissolved in hard sphere fluids are tested against Monte Carlo Widom insertion simulation measurements performed as a function of chain length (1⩽N⩽6), the ratio of the chain bead diameter to the solvent diameter (0⩽σ/σS⩽3), and solvent density (0.1⩽ρσS3⩽0.8). The results reveal a linear dependence of cavity formation energy on chain length for N⩾2. This allows extrapolation to chain lengths larger than can be measured by direct insertion. EVA predictions are found to be in good agreement with direct simulation results as well as long chain length extrapolations (up to N=50). As an illustration of potential practical application of these results, the EVA model is used to predict the cavity formation free energy of n-hexane dissolved in water and in the pure n-hexane liquid as a function of temperature and pressure, throughout the liquid temperature range.