Influence of microroughness on the wetting properties of nano-porous silica matrices

Abstract

AbstractWe report experimental measurements of the contact angle for four liquids on four different silica substrates, the systems covering a wide range of wettabilities. One of the substrates is a smooth planar silica surface, while the others have rough surfaces and meso-pores. We discuss the measured contact angles in relations to the microscopic wetting parameter, αw. This parameter emerges naturally from a corresponding states analysis of the partition function for this system, and is a measure of the ratio of the liquid–substrate intermolecular interaction to the interaction between two of the liquid molecules. Thus, it is a well-defined measure of wettability at both the nano- and macro-scales. The microscopic wetting parameter is shown to be a monotonic function of the contact angle. The contact angles for the materials with rough surfaces are found to be larger than those for the smooth planar surface for all liquids studied, including both non-wetting and wetting liquids. These results are discussed within the framework of a modified Cassie–Baxter model, in which only a fraction f of the liquid–solid interface is in actual contact with the solid. This fraction f is shown to increase as the wetting parameter increases in a physically reasonable way.Keywords: wettingnano-porous silicacontact anglesurface roughness AcknowledgementsWe would like to thank Prof. A. Derylo-Marczewska and Prof. L. Holysz and her co-workers from the Faculty of Chemistry, Marie Sklodowska Curie University, Lublin, Poland, for their kindness and help in synthesis and wettability measurements using KSV, Sigma700, Finland.Additional informationFundingThis work was supported by the Poland Operational Program 'Human Capital' [grant number PO KL.4.1.1] and National Science Centre [grant number DEC-2013/09/B/ST4/03711]; the US National Science Foundation [grant number CBET-1160151].