Adsorption and Capillary Condensation in Nanogap With Nanoposts

Adsorption isotherm and adsorption-capillary transition theories have been developed based on homogeneous micro-/nanoporous materials and structures. However, material and structures are often heterogeneous including local surface roughness and defects, where no predictive tool is available so far. In this study, the adsorption isotherm and the adsorption-capillary transition is examined for Ar-filled Pt nanogap (L_z = 5 nm) with nanoposts (one surface only) using Grand Canonical Monte Carlo (GCMC) simulations. Results show that the presence of the nanoposts causes a bimodal capillary transition and reduces the capillary transition pressure compared to the nanogap with both bare surfaces. The pressure difference between the bimodal transitions is pronounced with decreasing the nanopost pitch size. The larger nanopost height also leads to the early capillary transition, but the bimodal transition is pronounced for moderate heights of the nanoposts. A stronger solid-fluid interaction reduces the adsorption-capillary transition pressure at given temperature and increases the transition pressure difference between the nanogaps with or without nanoposts. The obtained results provide new insights of the role of surface nanostructure (nanoposts) into adsorption isotherm and capillary transition.