Conformal Sites Model for Adsorbed Films on Energetically Heterogeneous Surfaces

Molecular simulations and theoretical analyses of thin films adsorbed onto solid surfaces or within narrow pores have usually treated the solid surfaces as atomically smooth and energetically homogeneous. Most surfaces,... [ view full abstract ]

Molecular simulations and theoretical analyses of thin films adsorbed onto solid surfaces or within narrow pores have usually treated the solid surfaces as atomically smooth and energetically homogeneous. Most surfaces, however, exhibit roughness through geometric curvature, variations of surface composition and chemical groups attached to the surfaces. Such oversimplification of the surfaces thus misses important features of adsorption, especially at low bulk pressure. In this research, a flexible conformal sites model, mapping a real interfacial system with an energetically heterogeneous surface onto a reference system with an energetically homogeneous surface, is developed. Grand Canonical Monte Carlo simulation is used to explore the limits of applicability of this model to the prediction of adsorption isotherms. Preliminary simulation results showed that our conformal sites theory is quite successful in reproducing the adsorption behavior in non-polar systems and in slightly heterogeneous polar systems. Due to the simplicity and accuracy of the theory, we anticipate this new method will be incorporated in the software of experimental instrument to study porous materials by taking advantage of the corresponding states theory.