Water Adsorption on Kaolinite Surfaces Containing Trenches.

Recent lab. studies of water adsorption on kaolinite at 296 K, and at relative humidity (RH) values relevant for the atm., have reported coverages ranging up to tens of monolayers. But recent simulations suggested that atomistically smooth kaolinite surfaces uptake only monolayers (some slightly overgrown) at similar RH values. In an effort to possibly explain the lab. data, the authors have performed water adsorption calcns. on kaolinite surfaces contg. trenchlike structures using the grand canonical Monte Carlo simulation method at 298 K. The granularity of the surfaces can play a major role in the adsorption of multiple layers of water. For all trenches considered, multilayers of water were obsd. over a large range of RH. The narrowest trench studied remained filled with water even in the very low RH regime ( <= 0.0003%). Increasing the trench width resulted in partial or complete trench filling depending on the RH value, with large water mounds growing on the step edges. This strong affinity for water is explained by very attractive water-lattice interactions inside the trenches, esp. near the walls. The calcns. suggest that water adsorption in trenches, and possibly in other similar defects, can offer an explanation of the exptl. results. [on SciFinder(R)]