Paper surface modification by plasma deposition of double layers of organic silicon compounds

Abstract

In this work, filter paper was coated with plasma depositions of hexamethyldisilazane (HMDS), and double layers of HMDS and n-hexane, and HMDS and tetraethyl orthosilicate (TEOS). In the case of double layers of HMDS and TEOS, TEOS deposition times of 2, 4 and 6 minutes were studied. The double layers were interfaced by an intermixing layer, in which both reagents were present. All coating films formed adhered well to the substrate, and resulted in water repellent paper surfaces with apparent water contact angles above 100 degrees and water adsorption around 15 g m−2. Apparent water contact angles were not affected by immersion in strong basic and acid solutions, or by exposure to ultraviolet light for 106 hours. Water adsorption of HMDS, HMDS–n-hexane and HMDS–TEOS (6 min) coated samples was not significantly altered by these resistance tests, but HMDS–TEOS (2, 4 min) coated samples were hydrolysed by immersion in strong basic solution and by ultraviolet light. These results seemed to indicate that the HMDS–TEOS intermixing layer was fragile and malformed. This hypothesis was confirmed by Raman and atomic force microscopies, which showed heterogeneous structures with very high peaks, and by XPS analysis, which indicated oxidation of carbonic species and crosslinkings together with elimination of ethylene gas probably triggered in the intermixing layer. The porosity of paper was not altered showing that all depositions were conformal. FTIR analysis of HMDS coatings indicated that the films formed were crosslinked by ultraviolet light showing its potential for outdoor applications.