Surface energy and its components as parameters determining wettability and aggregation state of selected clay minerals and soils.

In the present work problems related to surface free energy of different agricultural materials such as clay minerals, mineral soils, organic soils and forest litter were considered. Methodical investigations of surface free energy determination as well as fundamental investigations connected with the influence of the surface cations and organic substance on the wettability, free energy and interaction forces between clay minerals and soil particles were undertaken. The interaction forces between clay minerals and soil particles perform a fundamental role in aggregation, flocculation and forming of solids structure. In case of solids the surface free energy can be determined indirectly for example from the measured contact angles or from the adsorption values (by determination of film pressure jt) with appropriate theoretical assumptions. Such methods were applied in this paper to determine surface free energy components for clay minerals and soils. Because of difficulties in contact angle measurements by sessile drop method (especially for organic soils and humus) thin layer wicking or thin column wicking technique were applied. The investigations of penetration rates of water and organic liquids carried out for clay minerals and their mono ionic forms showed the close dependence between the kind of mineral and surface cation. The linear dependence of penetration rates was obtained at the lowest penetration times for bentonite and the highest for kaolin. The kind and properties (e.g. radius of hydrated ions) play in this case an important role. The empiric series of wettability, depending on clay mineral and surface cation were determined experimentally. Similar measurements were performed for clay minerals with increasing additions of humic acid and for different soils. On the basis of the measurements the surface free energy components apolar and polar (electron-acceptor and electron-donor) were calculated and correlated with the kind of clay mineral, surface cation and humic acid content. The investigations for soils show that the penetration times depend on the soil samples. Contact angle values for investigated samples were also calculated. From the water vapour adsorption measurements on the surfaces of modified clay minerals and soils the water film pressure values were calculated for one or three monolayers and compared with the work of adhesion and immersion. For soil materials surface free energy had real influence on structure formation or its changes. The organic matter and surface cations had an important role in creation of soil structure