Kapillärkondensation

Kapillärkondensation refers to the phenomenon where vapor condenses on the surface of a liquid within narrow pores or capillaries, even when the vapor pressure is below the saturation vapor pressure at that temperature. This occurs due to the curvature of the liquid surface within the capillary. The surface tension of the liquid creates a negative pressure (tension) within the liquid, which in turn lowers the equilibrium vapor pressure above it. This is described by the Kelvin equation.

The Kelvin equation quantifies the relationship between the vapor pressure above a curved liquid surface and the vapor pressure above a flat surface. The smaller the radius of the capillary, the greater the curvature of the liquid surface, and thus the lower the equilibrium vapor pressure. Consequently, condensation can occur at lower relative humidities in smaller pores compared to larger volumes.

This effect is significant in various natural and industrial processes. In soil science, kapillärkondensation plays a role in water retention and transport in porous media. In materials science, it influences the behavior of porous solids like activated carbon and zeolites, affecting their adsorption and desorption properties. It is also relevant in the drying of materials and the formation of dew or frost in confined spaces. The phenomenon highlights the impact of surface tension and geometric confinement on phase transitions.