Water repellency and infiltration resistance of organic-film-coated soils.

Water repellency and infiltration resistance of porous soils coated with a variety of thin, organic films were examined. Water repellency was determined by measuring the effective contact angle of water resting on the soil surface and infiltration resistance was determined by measuring the breakthrough pressure, i.e., the threshold pressure required to force water into the soil pore structure of these water-repellent soils. The effective contact angle of water on these treated soils was found to be a function of (i) the structure of the hydrophobic portion of the organic admolecules, and (ii) the proportion of soil surface covered with the organic film, but was relatively independent of soil chemical and physical properties. Effective angles as high as 150 to 160° were recorded for several types of organic materials. These included several silicone water repellents, an amine- and a hydroxy-substituted phenol, and an acetic acid salt of a long-chain fatty amine. The breakthrough pressure was directly affected by the factors that controlled the contact angle, and was inversely related to the effective pore radii of the porous, water-repellent soils.