Lattice density functional theory investigation of pore shape effects. II. Adsorption in collections of noninterconnected pores

A fully explicit three-dimensional lattice density functional theory is used to investigate adsorption behavior in collections of noninterconnected pores. The study focuses on the effects of external surfaces and the shape of individual pores on the adsorption and desorption isotherms. Pore shapes far more varied than the traditionally considered cylinders and slitlike pores allow a better assessment of the general role of pore geometry. Pore shapes that exhibit acute angles display significantly different adsorption and desorption branches. For most pores the presence of an exterior surface greatly reduces the extent of the hysteresis loop through meniscus formation. However, for sufficiently large pores a thick film present on the exterior surface can interfere with meniscus formation and lead to desorption controlled by the thick film. A comparison was made with recent experiments on well-characterized systems of noninterconnected pores. The calculations do not agree with the experimental adsorptions if the models are based on the pore types suggested by the experimental work. Improved agreement can be obtained by considering small bottlenecks along the length of the pores length. To establish the presence of such a feature would probably require more detailed experimental characterization.