Correlation functions of adsorbed fluids in porous glass: a computer simulation study

We have prepared a series of model porous glasses using a recently develope d molecular dynamics procedure (GELB, L. D. and GUBBINS, K. E., 1998, Langm uir, 14, 2097) that mimics the experimental processes that produce Vycor an d controlled pore glasses. Using Grand Canonical Monte Carlo simulations we have measured nitrogen adsorption isotherms in these models and determined the radial distribution functions and structure factors for the adsorbate at several different pressures. These correlation functions show long-wavel ength fluctuations which at low density are controlled by the glasses surfa ce-surface correlation functions and at high density are controlled by the glasses void-void correlation functions. The structure factor data at low d ensity can be used to extract a characteristic pore diameter which agrees w ell with that obtained by a geometrical analysis of the pore structure. Sig nificant qualitative differences in S(k) are found between 30% porous and 5 0% porous materials.