Hydrocarbon Vapour Adsorption on Porous Materials

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An advance has been made that allows the surface tensions of solids that are exposed to either a vapour or a liquid to be determined. This advance came after an adsorption isotherm was formulated for vapour adsorption on smooth solid surfaces when the vapour-phase pressure is between zero and the saturation-vapour pressure. The parameters in this isotherm expression can be determined from measurements of the amount adsorbed as a function of the vapour-phase pressure. Once these isotherm parameters are known for a particular vapour-solid system, they may be used in Gibbsian thermodynamics to obtain the expression for the surface tension of the solid-vapour interface as a function of the vapour-phase pressure. When the vapour-phase pressure is large enough so a sessile droplet can exist, the surface tension of the solid-liquid interface can also be predicted. Although neglected previously by others, one of the conclusions of our previous studies is that for a given temperature, the contact angle of a sessile droplet increases as the liquid-phase (or the vapour-phase) pressure increases. This conclusion has recently received strong experimental support. Based on these previous studies, we are extending our model to adsorption on porous materials. This model indicates that the reason the pores in a material exposed to a vapour fill at pressures below the saturation-vapour pressure is because the contact angle of the condensate within a pore increases as the vapour-phase pressure is increased.