2024 AIChE Annual Meeting
(346f) Nano-Wetting and the Effect of Confinement on the Phase Diagram
Author
Keith E. Gubbins - Presenter, North Carolina State University
A statistical mechanical analysis of the free energy density of a highly inhomogeneous nanoscale system of simple molecules is determined by a small number of dimensionless parameters, including the dimensionless width, H*, of the nanophase and a microscopic wetting parameter, αw, that is defined in terms of intermolecular forces and solid structure; αw is a measure of wetting that applies at all scales and for any kind of adsorbed film (gas, liquid or solid). We illustrate the usefulness of this approach using examples drawn from both experimental and molecular simulation studies of gas-liquid and liquid-solid phase separations, with emphasis on simple pore geometries. These examples illustrate the central role played by wetting, and also the breakdown of some concepts and macroscopic laws, such as the equations of Kelvin, Laplace and Gibbs-Thomson, for nano-phases confined within small pores. They also suggest consistency tests for experimental data that should be applied in the event of capillary condensation or other phase changes in mesoporous materials. The approach can be extended to account for geometric or energetic wall roughness, and pore wall curvature. The recent simulation results for the melting line and triple point in pores show some features that have not yet been studied experimentally, such as re-entrant melting behavior for weakly wetting systems and large changes in slope of the melting line near the triple point.