SURFACE-ROUGHNESS EFFECTS IN MOLECULAR-MODELS OF ADSORPTION IN HETEROGENEOUS POROUS SOLIDS

We present an investigation of the influence of surface roughness on t he interior pore walls upon adsorption equilibrium in heterogeneous po rous materials using molecular models of methane adsorbed in a micropo rous silica gel. The molecular models treat the adsorbent as a disorde red matrix of particles. Three different models of the surfaces of the matrix particles are considered where (i) the adsorbent particles exh ibit smooth surfaces, (ii) the particle surfaces have a single layer o f interaction sites, and (iii) atomic details of the matrix particles are incorporated. The effects of surface roughness in these models are most appreciable on the isosteric heat at low density. The effect on the adsorption isotherm comes principally at higher pressure due to an increase in the effective void space produced by the surface roughnes s. A comparison with experimental data is also presented.