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Solubilities of additive molecules whose molecular sizes exceed the typical dimensions of free volume cavities pre-existing in amorphous polymer melts and glasses cannot readily be computed in molecular simulations. In this paper, we perform molecular dynamics simulations of a soft-cavity reference state ensemble, which contains a soft-core, fast diffusing, Lennard-Jones particle in a rigid-chain polymer matrix. By means of the Zwanzig thermodynamic perturbation formalism, the soft particle has been perturbed to various real-solute end-states. It is shown that with this approach it is possible to overcome some of the free energy sampling problems related to the insertion of large solutes and slow diffusion in the end-state. We have calculated the excess chemical potentials of propane, chloroform, and dimethyl sulfoxide in liquid bisphenol A−polycarbonate and show that a single simulation of the reference state is sufficient to obtain statistical accuracies within error bars of 0.5−0.8 kBT. The method is particularly useful for calculating solubility ratios of large molecular solutes with approximately equal excluded volume radii. [ABSTRACT FROM AUTHOR]

We have calculated excess chemical potentials of additive molecules in a bisphenol A-polycarbonate matrix using fast-growth thermodynamic integration. It is shown that this method, which is based on Jarzynski's nonequilibrium work theorem, is ideally suited to overcome some of the typical sampling problems one meets when inserting large additive molecules into a dense polymer matrix. The method provides a direct link between the calculated excess chemical potential and the atomic-scale environment preferred by the inserted molecule. We discuss for which types of free-energy landscapes fast-growth thermodynamic integration is well suited and which are the optimal parameters to use. [ABSTRACT FROM AUTHOR]

Solvation enthalpies of simple solutes contain contributions from (1) solute−solvent interactions and (2) solute-induced modifications of solvent−solvent interactions (solvent reorganization). It has recently been suggested in the literature that these contributions can, under certain conditions, be estimated with additional experimental data on thermodynamic response functions of the pure solvent (coefficient of thermal expansion, isothermal compressibility) and the solute solvation volume. We analyze and discuss these conditions based on computer simulations of a series of polar and nonpolar solutes in a polar and nonpolar liquid solvent. [ABSTRACT FROM AUTHOR]