Contact angle hysteresis in the clay-water-air system of soils

Abstract

© Springer Nature Switzerland AG 2020. Microorganisms emit substances changing the surface tension of soil solution and the surface energy of solid soil particles. Clays and soils have high heterogeneity of the surface energy distribution among particles. The change in the surface energy of soil particles is caused not only by alteration of their chemical properties but also an increase/decrease in their spatial heterogeneity, which determines contact angle hysteresis. Available techniques of measurement the contact angle and the contact angle hysteresis require further improvement and adaptation to specific clay types. The purpose of this research is to study the change in wettability of clays due to the influence of mesophilic soil microorganisms’ activity when adding model contaminants: water-in-oil emulsion, glycerol and oleic acid. During the experiments, the objectives of this study were to specify peculiarities of wetting contact angle hysteresis of clays with substrates of different mineral composition and microbial activity. Hydrophilicity/hydrophobicity of the stimulator for microbial activity does not have a clear effect on clay properties. The surface heterogeneity mostly increases with time, perhaps, due to biofilm exudates whatever was a type of microbial stimulator. Chemical and geometric heterogeneities played comparable roles in the surface hydrophilic-hydrophobic balance. Results obtained prove that microbial communities and/or the Fe chemical state alteration (pyrite, hematite or goethite) were responsible for both hydrophilization and hydrophobization of the surface. The equation for the drop spreading rate was presented and verified by well comparison of experimental results with simulations.