Transport diffusion of liquid water and methanol through membranes

In this work, we carried out dual-control-volume grand canonical molecular dynamics simulations of the transport diffusion of liquid water and methanol to vacuum under a fixed chemical potential gradient through a slit pore consisting of Au(111) surfaces covered by -CH3 or -OH terminated self-assembled monolayers (SAMs). Methanol and water are selected as model fluid molecules because water represents a strongly polar molecule while methanol is intermediate between nonpolar and strongly polar molecules. Surface hydrophobicity is adjusted by varying the terminal group of -CH3 (hydrophobic) or -OH (hydrophilic) of SAMs. We observed for the first time from simulations the convex and concave interfaces of fluids transporting across the slit pores. Results show that the characteristics of the interfaces are determined by the interactions between fluid molecules and surfaces. The objective of this work is to provide a fundamental understanding of how these interactions affect transport diffusion. (C) 2002 American Institute of Physics.