Capillary condensation and desorption of binary mixtures of N-2-Ar confined in a mesoporous medium

The adsorption and desorption of the binary system N2xAr1-x confined in the cylindrical 4 nm diameter pores of Vycor glass has been studied using posi tron annihilation spectroscopy. When the Vycor sample was suspended in the gaseous mixture, the gas-liquid and liquid-gas phase transitions of the con fined fluid exhibit hysteresis which varies little with composition, indica ting that the confined mixture behaves like a simple fluid. However, if bul k mixture surrounding the samples was allowed to condense, the liquid-gas t ransition exhibited a much larger degree of hysteresis for the mixtures; al though unchanged for either pure gas. The observed behavior indicates that bulk liquid condensed around the Vycor samples is able to interact with the confined fluid, causing the confined mixture to become Ar rich.