Porous membranes based on polyvinyl chloride: preparing by the method of phase inversion and its properties

Porous polymeric membranes based on unstabilized polyvinyl chloride (PVC) with a con-centration of 7, 9, and 11 wt% were obtained by the phase inversion method. Dimethylformamide (DMF) was used as a solvent. The structure of the membranes studied from SEM images shows a significant dependence on the exposure time and the composition of the atmosphere during expo-sure. The sample aged for 30 s in an atmosphere of saturated solvent vapor has a uniform spongy structure, which differs from all other samples aged in air, which have a structure classic for this kind of synthesis method: two skin-layers and finger-shaped vertical pores. With an increase in the concentration of casting solutions, the thickness of the membranes, density, and minimum hydro-static pressure increase; shrinkage is reduced. A sample made from 11wt% PVC solution, kept in air for 10 s, is hydrophobic, has a contact angle of 104.3 & DEG;, for the rest the contact angle lies in the range of 62-82 & DEG;. Wetting of porous materials strongly depends on the nature of the surface, the hydrophobic properties of this sample are associated with many small surface pores, which is con-firmed by the maximum value of LEP (liquid entry pressure). Interestingly, the properties of the skin-layer in direct contact with water are rather homogeneous for all samples, while for the skin -layers adjacent to the glass substrate significant differences are observed for different samples and a complex hierarchical pore structure resembling breathing figures. The pore sizes were evaluated using the ImageJ image processing and analysis program in Java. The pore sizes are in the 0.03-0.5 & mu;m range. It has been determined that the properties of the obtained membranes generally meet the requirements for the materials for membrane distillation, and the method of their synthesis allows flexible control of the structure.