Reexamination of capillary phenomena in cylindrical pores and application to pore size analysis

The way to account for curvature dependence of the surface tension in capillary phenomena is reexamined for the case of cylindrical pores (Section 2). The relationship between γ, the interface area s and the adsorbed quantity N is discussed and it is suggested that the change d(γs) should be considered in the free enthalpy calculation instead of γds. In opposition to a recent paper this refinement introduces only small changes in adsorption layer thickness and in equilibrium evaporation pressures. Attention is focused on the length assumption which is always in treatments of the cylindrical pore model (Section 3). Only in a few instances have long cylindrical pores been identified [14, 15]. In ordinary porous material, when the cylindrical model can be regarded as fitting, most pores will at best be short segments. Quantitative corrections for this departure from ideality cannot be introduced, for the average length in a pore class is not known. However, it is interesting to evaluate the magnitude of the errors involved. The Broekhoff-de Boer treatment of the meniscus curvature and shape provides the basis for such an evaluation (Section 4). The low results often obtained from the adsorption isotherm can, at least partially, be explained by the assimilation of short pores to long ones.