(291p) Grand Canonical Monte Carlo Simulation Study of Capillary Condensation in Nanocontacts Zone

Capillary condensation at the nanoscale differs from general condensation phenomena in bulk phase, because it is strongly a function of surface geometry and gas-surface interactions. Here, the effects of geometry on the thermodynamics of capillary condensation in the neck region between nanoparticles are investigated via a grand canonical Monte Carlo simulation of a 2-dimensional lattice gas. The microscopic details of the meniscus formation on various surface geometries are examined and compared with classical macromolecular theory such as Kelvin equation. In this study, we assume that the system is composed of lattice gases and substrate surfaces with various geometries, and we investigate the effects of surface-fluid interaction, saturation, and temperature. The nanoparticles are titania, and the condensing species is tetraethoxy orthosilicate (TEOS). This system was chosen because results can be compared to experimental studies of these same materials. The surface-fluid interaction is characterized based on the TEOS wettability on titania surface and the lattice gas properties are derived from molecular properties of TEOS. Qualitatively, our simulation results show that the particular geometry in the capillary zone, the fluid-solid interaction, and saturation condition are important for determining the onset and broadening of the liquid phase. The meniscus height is determined using a criteria of average lattice site occupancy of greater than 0.5 to indicate the presence of liquid. Simulation results indicate that the meniscus height is continuously increasing as the saturation ratio increases and the meniscus broadens faster above the saturation ratio of 0.95.