Kapillaradsorption

Kapillaradsorption, or capillary adsorption, denotes the uptake of a liquid by a solid through capillary forces in porous materials. It encompasses adsorption on solid surfaces and capillary condensation within pores, allowing liquid to reside in narrow pores at relative vapor pressures below the bulk liquid's saturation. It is common in hydrophilic porous media such as clays, silica, cement, and activated carbons.

In porous solids, surface-adsorbed films form on pore walls; when confinement is strong, the liquid can condense within pores at partial pressures described by the Kelvin equation, generating capillary condensates and menisci that sustain liquid inside pores.

Key factors include pore radius distribution, pore geometry, surface energy and contact angle, temperature, and the chemical potential of the liquid (e.g., relative humidity for water). Smaller pores condense at lower humidity; higher contact angles suppress capillary uptake.

Common materials include clays, cement paste, silica gels, porous glass, and activated carbon.

Applications of Kapillaradsorption span moisture buffering in buildings, the durability of construction materials, soil moisture studies, catalysis, and gas storage or separation.

Measurement and theory: adsorption isotherms (Langmuir, BET) describe films on surfaces, while capillary condensation in pores is modeled with the Kelvin equation and capillary pressure; pore-size distribution methods and sorption measurements are used to characterize the phenomenon.