Surfactant solutions and dispersed systems at superhydrophobic surfaces in air and liquid environment

Amphiphilic molecules and dispersed systems in contact with highly water-repellent solid surfaces play key roles in research and technology, with increasing interest in different fields. Nevertheless, the wetting properties of aqueous surfactant solutions, non aqueous liquids or immiscible phases as in foams and emulsions on such superhydrophobic (SH) solid surfaces have been so far rarely investigated.[1] From selfcleaning materials to microfluidic devices many applications can exploit the wetting characteristic of nature-inspired surfaces showing contact angle above 150° and a very small hysteresis. In this work the SH surfaces were prepared by a mixed inorganic-organic coating on different substrates and studied in presence of different systems. Depending on the preparation SH surfaces show different aging resistance due to the composition and thickness of the hydrophobizing coating layer. Surfactant adsorption results in a switch between a Cassie-Baxter and a Wenzel regime for superhydrophobic surfaces at water-air. The partitioning features of surfactants strongly affect the oil-water interface wetting properties resulting in a switch between a Wenzel and a Cassie-Baxter regime.[2] Reference: [1] Ferrari M. Aqueous and Non-Aqueous Liquids on Superhydrophobic Surfaces:Recent Developments in Contact Angle, Wettability and Adhesion, Volume 6 Ed.K. L. Mittal, Brill- VSP (The Netherlands) 269 (2009). [2] Ferrari M., Ravera F. Surfactants and wetting at superhydrophobic surfaces: Water solutions and non aqueous liquids. In: Advances in Colloid and Interface Science, vol. 161 (1- 2) pp. 22 - 28. Physico-chemical and flow behaviour of droplet based systems. V.M. Starov, R. Miller, S. Guido (eds.).Elsevier B.V,2010