A Study On Soil Contact Angle And Soil Surface Free Energy Properties

Wettability is a normal phenomenon, and contact angle is a direct and simple index. Soil wettability is one of soil important hydrological properties, and it is closely related to the crust, soil loss, the formation of preferential flow, and the generation of surface runoff. The soil surface free energy could be calculated by measured soil contact angle. The soil wettability research could provide scientific data for further studying on soil properties.Some soils were used to research contact angle by capillary rise methods based on Washburn's equation, such as Lou soil from Henan, Lianghe soil from Hebei, Purple soil, Yellow soil and Lime soil from Chongqing, and Huangmian soil from Shanbei. The relationship between soil wettability and soil category, aggregate size and soil physicochemical properties were analyzed. At the same time, the soil surface free energy and its components were calculated. The main results were concluded as follows:(1) The contact angles of water, Formamid and n-Dodecane of different particle-size soils were measured with the aggregate size <0.074mm, 0.074-0.25mm, 0.25-1.0mm and 1.0-2.0mm. The contact angle for every size soil were different for different wetting liquids, and the contact angle for each wetting liquid were different for soil size. There had a general tendency that the contact angle decreased along with soil size increasing, that showed the wettability of soil became better along soil size increasing. The soil size, category and components were all the effecting factors for soil wettability.(2) Soil surface free energy and its components were different with different particle-size. With the increase of soil aggregate size, the total surface free energy, polar free energy and dispersion free energy increased. The polar of wetting liquid had brief influence on soil contact angle, and there was a general tendency the wettability becoming worse along the polar becoming greater.(3) The soil that the size was less than 0. 074mm with the same parent materials under different vegetation were measured, and the wettability had greater difference. One reason maybe that the hydrophilic and hydrophobic properties of soil organic matter from different litter under different vegetation. But there was a notable linear relationship that the soil contact angles become larger with soil organic matter increasing.(4) There was phenomenon that the soil erodibility became small with soil organic matter increasing. One possible reason was: the wetting velocity affected the soil aggregate rupture speed; the repellency of soil organic matter slowed the wetting velocity and decreased the soil aggregate rupture. Thus the worse wettability decreased soil erodibility.