Bridging the gap between mesoscopic and molecular models of solid/liquid interfaces out-of-equilibrium

Abstract

Solid/liquid interfaces control various processes of technological relevance in the process industry and many fundamental physicochemical phenomena. This work examines the link between the atomistic description of mass transfer at solid/liquid interfaces out of equilibrium and constitutive mass transfer equations which are typically used to model these processes at the mesoscale. In our analyses we discuss the microscopic inconsistencies apparent in simplified models of mass transfer whenever non-idealities dominate the liquid phase in the proximity of solid/liquid interfaces. Using CμMD – a molecular simulation technique to investigate out-of-equilibrium, concentration-driven processes with pseudo open-boundary conditions – we outline a strategy to capture and quantify non-idealities induced by specific interactions between the solid surface and molecules in the fluid phase. We demonstrate our approach by studying electrolyte solutions in technologically important, multi-component systems where the introduction of a solid/liquid interface induces substantial deviations in the composition and electrochemical properties locally compared to the bulk fluid phase. To this aim, we analyse NaCl(aq) solutions in contact with (i) the graphite basal surface and (ii) {100} NaCl(s) crystalline surfaces. We uncover the tendency of the sodium cation to preferentially adsorb at the surfaces considered, which induces local violations of electroneutrality that leads to the emergence of an electric potential in the fluid phase at the solid/liquid interface.