Formation of Hydrophobic Coatings on the Surface of Track-Etched Membranes Using Magnetron Sputtering of Polymers in Vacuum

The surface properties and chemical structure of nanosized coatings deposited on the surface of polyethylene terephthalate track-etched membranes by magnetron sputtering of ultrahigh molecular weight polyethylene and polytetrafluoroethylene in a vacuum have been studied. Application of coatings leads to hydrophobization of surface of the original membranes, the degree of which depends on the type of polymer used for sputtering and the coating thickness. The use of this modification method causes smoothing of structural inhomogeneities of the surface layer of membranes, which is explained by the deposition of coatings in the pore channels at a certain depth from the inlet and the overlap of pores on the surface of modified membranes. In addition, the deposition of coatings on the surface of track-etched membranes leads to a change in the shape of pores. The pore diameter decreases significantly on the modified side and remains unchanged on the untreated side of the membrane, while the membrane pores acquire an asymmetrical (conical) shape. The study of chemical structure of coatings using X-ray photoelectron spectroscopy showed that they contain oxygen-containing functional groups owing to oxidation of the polymer matrix. The developed composite membranes can be used in membrane distillation processes for seawater desalination.