Sorptiviteit

Sorptiviteit, sometimes rendered as sorptivity, is a property of a porous material that describes its capacity to absorb a liquid by capillary action, especially during the early, gravity-neutral stage of infiltration into an initially dry medium. It is a measure of how readily liquid can move into pore spaces due to capillary suction, before gravity dominates transport.

In infiltration theory, sorptivity is represented by the parameter S in the Philip equation for cumulative infiltration: F(t) = S t^0.5 + K t, where F is the total infiltrated volume, t is time, and K is the saturated hydraulic conductivity. From this relation, the infiltration rate i(t) = dF/dt can be written as i(t) = S/(2 sqrt(t)) + K. The units of S are length per square root of time (for example cm/√min). Sorptivity depends on the pore structure and wettability of the material, and it typically decreases as the soil becomes wetter or the pore network becomes more tortuous.

Determinants of sorptivity include pore-size distribution, connectivity and tortuosity of the pore network, initial moisture content, surface properties, and temperature. In practice, S is higher for materials with well-connected capillary pores and strong capillary forces, and it diminishes as the material gains moisture or undergoes aging.

Measurement and estimation commonly use infiltration tests on dry specimens. By recording cumulative infiltration over time and plotting F versus sqrt(t), S is obtained from the linear early-time portion, while K is inferred from the long-time behavior. Sorptivity is widely used in hydrology, soil science, and civil engineering to model rainfall infiltration, moisture transport in soils and porous building materials, and initial moisture changes in pavements and barriers.