Dimensional Changes Accompanying Capillary Condensation

Abstract

Banks and Barkas¹ have recently directed attention to the mechanical interaction between capillary condensed liquid and the walls of the pores containing it, and they deduce that under certain conditions the pores may collapse when the vapour pressure over the system is lowered. However, when capillary condensation occurs, the liquid condenses on an adsorbed film—not on a bare surface—and it is to be expected that when the vapour pressure is sufficient to cause condensation of liquid, there will always be present an adsorbed film which is mobile. A mobile film exerts a pressure² numerically equal to the free-energy lowering per unit surface due to its adsorption, and in a capillary tube this pressure opposes the tension of the condensed liquid. Effects due to the pressure of a surface film have been neglected by Banks and Barkas in their calculations.