Kapillärdensättning

Kapillärdensättning, often translated as capillary condensation, is a phenomenon observed in porous materials where vapor condenses in the pores at a relative humidity lower than the bulk saturation vapor pressure. This occurs due to the curved surface of the condensed liquid within the pores, which leads to a lower vapor pressure over the curved interface compared to a flat surface.

The relationship between the pore size, the surface tension of the liquid, and the vapor pressure is described by the Kelvin equation. The Kelvin equation shows that as the pore radius decreases, the relative humidity at which capillary condensation occurs also decreases. This means that smaller pores will fill with condensed liquid at lower relative humidities than larger pores.

This phenomenon has important implications in various fields. In soil science, it influences the water retention capacity of soils, affecting plant growth and water availability. In materials science, capillary condensation can contribute to the degradation of porous materials due to the increased stress exerted by the condensed liquid. It is also relevant in adsorption processes, where the multilayer adsorption of vapors on solid surfaces can be understood as a series of capillary condensations within the micro- and mesopores of the adsorbent. Understanding kapillärdensättning is crucial for predicting the behavior of porous materials in humid environments.