Cavity formation free energies for rigid chains in hard sphere fluids

Abstract

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.

Pressure and temperature-dependent gauche-trans isomerization of 1-bromopropane: Raman measurement and statistical thermodynamic analysis

“…28,29 The present work, and previous solvation free energy calculations, 10 illustrate applications of the EVA model to molecular liquid thermodynamic calculations. In order to perform such calculations reliably, it is very important to choose an appropriate effective hard sphere diameter for the solvent.…”

“…3,7,8 In particular, the perturbed hard-body fluid ͑PHF͒ formalism used in this work treats the solution of interest as a repulsive reference fluid with a van der Waals mean field of attractive intermolecular interactions. This approach, which has previously been applied to a variety of molecular solvation, reaction and vibration processes, [7][8][9][10][11][12][13][14][15] is here used to interpret temperature-and pressure-dependent changes in the gauche-trans isomer population ratio in liquid 1-bromopropane ͑see Fig. 1͒, by comparing theoretical predictions with Raman spectroscopic measurements.…”

Improper matching of solvation energy components in Gex-based mixing rules

“…It should be noted here that the decomposition of the solvation free energy used here is slightly different from the formal definition for the cavity formation and charging processes [16], in which only the solute molecule (and not the solvent) is being charged from the state of a hard particle. Here the cavity formation free energy corresponds to the insertion of a hard particle in to a fluid of hard particles [18][19][20][21][22]; and the charging free energy corresponds to that of charging the solute and solvent molecules simultaneously.…”

Hydrophobic Effects on a Molecular Scale

“…69,70,71,72,73,74 Similar insertion methods were also used to study polymer solubilities. 75 The simulation studies of Pohorille and Pratt 69,70,71 clarified a number of interesting speculations on hydrophobicity and provided the first discriminating tests of theoretical models for G(λ). Figure 4.…”