Method To Determine Apparent Contact Angle Of Liquids On Granules Surfaces

Granular materials are widely used in various fields, and their surface wetting properties greatly affect the interface performance and the overall performance of the materials. As an important physical parameter, the contact angle can well characterize the wettability and free energy of liquids on the solid surfaces, so research on measuring contact angle has great significance in materials development and application. At present, the measurement of the contact angle is usually confined to solid materials with smooth plat surface. However, it is difficult to measure the apparent contact angle of liquids on the solid surfaces which are neither smooth nor flat. Studies shows that the critical moisture content, which is related to the transition point of liquids morphologies and distribution changing, is determined by the apparent contact angle of liquids on granular surface. In view of this, on the basis of the relationship between the critical liquid content and the contact angle, this paper attempt to determine the apparent contact angles of liquids on granules surfaces by determining critical liquid contents.There are two ways used to obtain the critical liquid contents in this paper. One is through microscopic observation, another is by electrical conductivity measurements. By microscopic observation, the liquids morphologies and distributions in granular porous media are analyzed and determine the critical liquid contents. Studies show that the overall electrical conductivities of porous media constituted by non-conductive granular are closely related to the morphology of conductive liquids distributed in the media. Therefore, for samples formed by non-conductive granules and conductive liquids, the critical liquid content can be determined by electrical conductivity measurement if it is difficult to observe the liquid morphologies in the wet samples.After measuring the contact angle of liquids on the surfaces, the non-conductive plate glass and slide glass are broken and be processed in to small particles, and then classified according to their sizes. With different liquids, the wet samples electrical conductivities and the volume change rates versus different liquid content were measured. Combined with critical liquids contents determined and the contact angle obtained from the plate glass and slide glass, the equation of the relationship between contact angles and the critical liquid contents was verified. Based on this, this paper obtained the method to determine the contact angles of liquids on granules surfaces.As irregular particles samples with range, the contact angle of liquids on sand particles surfaces were determined with different sizes samples. Together with samples volume change rate measured, the critical liquid contents were determined by the electrical conductivities tests and micro observation experiments. Combine with the relation equation of the contact angles and critical contents, the contact angle of liquids on sands surfaces were obtained.