On the use of molecular simulations to study homogeneous and inhomogeneous associating fluids.

摘要

Molecular simulation has proven in the last decades to be an important tool both in the development of theories for complex fluids and as a media to study complex thermodynamic systems when experiments and theory are impractical or unavailable. This work presents two examples of the use of molecular simulations as applied to the study of associating fluids. In one case simulations are used to improve on theories for homogeneous associating fluids; in the second case molecular simulations are used to study the adsorption of associating fluids in surfaces.;Computer simulations are used here to study Wertheim's theory for bulk-phase associating fluids and to extend it to attractive potentials, chains and polar molecules. The accuracy of the first order perturbation theory is seen to depend strongly on the quality of the prediction of the non-associating reference potential properties, particularly the two-body correlation function. Second and higher order corrections to the theory are shown to be of lesser importance in most cases of practical interest. These findings ultimately lead to the presentation of an engineering equation of state applicable to anisotropic fluids, e.g. chain molecules and polar fluids in which association is present.;The adsorption of associating fluids onto surfaces and pores is studied using molecular simulations. In this case, theories are not yet available and experiments can not resolve the adsorption process on a molecular level. Adsorption isotherms are calculated for both model associating chains and water in activated carbons. Increased absorption is observed in these systems when the surfaces are doped (activated) with associating sites. The density and placement of the sites have a crucial effect on the adsorption isotherms. For the first time, evidence is given here that the adsorption of water in activated surfaces proceeds by means of clustering rather than layering on the surface.