Molecular simulation of micro-structures and gas diffusion behavior of organic–inorganic hybrid amorphous silica membranes

A molecular dynamics (MD) technique using h-pcff force field was adopted to analyze the micro-structure and gas transport behavior of an organic–inorganic hybrid bis(triethoxysilyl)ethane (BTESE) silica membrane. The membrane fractional free space (FFS), cavity size distribution (CSD), and fractional accessible volume (FAV) were estimated to discuss how doped Si–C–C–Si segments affect a silica network. The radial distribution function (RDF) of atom pairs was analyzed to investigate the micro-structure of a hybrid silica network. The gas diffusion behavior, including the thermal motion and diffusivity, was calculated to understand the gas transport behavior of the BTESE silica membrane. The analyses of the FFS, CSD, and FAV of the silica membrane indicated that the silica network would expand to form a larger cavity size, indicating a high potential for increased gas permeance. The RDF diagram indicates that the hybrid silica matrix provides a looser structure with higher network fluctuation than that of the pure silica membrane. The gas diffusion behavior analysis revealed that the hybrid silica membrane contained more effective free space, which prompted H2 diffusivity and also produced a good H2/SF6 diffusivity ratio. The MD technique was successfully applied to simulate the characteristics and gas diffusion behaviors of the hybrid BTESE silica membrane. Demonstration of the superior properties of hybrid BTESE silica using MD technique proves itself to be a promising tool for material development and design on a microscopic view.