Modeling solubilities of additives in polymer micro structures: Single-step perturbation method based on a soft-cavity reference state


Oezal T. A. , Peter C., Hess B., van der Vegt N. F. A.

MACROMOLECULES, vol.41, no.13, pp.5055-5061, 2008 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 41 Issue: 13
  • Publication Date: 2008
  • Doi Number: 10.1021/ma702329q
  • Title of Journal : MACROMOLECULES
  • Page Numbers: pp.5055-5061

Abstract

Solubilities of additive molecules whose molecular sizes exceed the typical dimensions of free volume cavities pre-existing in amorphous polymer melts and glasses I 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 k(B)T The method is particularly useful for calculating solubility ratios of large molecular solutes with approximately equal excluded volume radii.