Purpose From self-cleaning 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. Adsorption and wetting studies regarding amphiphilic molecules and adsorption properties on 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 on superhydrophobic (SH) solid surfaces have been so far rarely investigated. Transition between wetting states can be also considered a possible development of these studies based on switching mechanisms. Materials and methods In this work the SH surfaces were prepared by a mixed inorganic-organic coating on different substrates and studied in presence of different surface active molecules. UV photolithography has been used to prepare patterned surfaces, then hydrophobized by silanization using OTS solution in toluene with and without previous alumina nanoparticles deposition. Ionic and non-ionic surfactants have been used also in presence of electrolytes. Contact angle measurements have been performed by ASTRAView drop profile tensiometer in a temperature controlled chamber both at liquid-air and liquid-liquid environment. Results Depending on the preparation SHS show different aging resistance due to the composition and thickness of the hydrophobizing coating layer. Increasing surfactant adsorption results in a switch between a Cassie-Baxter and a Wenzel regime for superhydrophobic surfaces at water-air. At oil-water interface wetting properties are strongly affected by the partitioning features of surfactants resulting in a switch between a Wenzel and a Cassie-Baxter regime. The presence of salts and the surfactant solution concentration is effective to decrease the contac angle and the effect of the roughness plays a role in maintaining a high hydrophobic effect. Conclusions The dependence of the wetting properties on different parameters like surfactant type and concentration show how the presence of amphiphiles is effective in lowering the contact angle in a hydrophobic or still superhydrophobic range. By coupling the adsorption properties and the repellence of the solid surface, the drop spreading can be controlled confining its volume in a restricted space. References Krasowska M., Ferrari M., Liggieri L., Malysa K. Influence of n-hexanol and n-octanol on wetting properties and air entrapment at superhydrophobic surfaces Phys. Chem. Chem. Phys., 2011, 13, 9452-9457. 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.
Adsorption and wetting properties of surfactant solutions at superhydrophobic surfaces in air and liquid environment
2011
Abstract
Purpose From self-cleaning 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. Adsorption and wetting studies regarding amphiphilic molecules and adsorption properties on 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 on superhydrophobic (SH) solid surfaces have been so far rarely investigated. Transition between wetting states can be also considered a possible development of these studies based on switching mechanisms. Materials and methods In this work the SH surfaces were prepared by a mixed inorganic-organic coating on different substrates and studied in presence of different surface active molecules. UV photolithography has been used to prepare patterned surfaces, then hydrophobized by silanization using OTS solution in toluene with and without previous alumina nanoparticles deposition. Ionic and non-ionic surfactants have been used also in presence of electrolytes. Contact angle measurements have been performed by ASTRAView drop profile tensiometer in a temperature controlled chamber both at liquid-air and liquid-liquid environment. Results Depending on the preparation SHS show different aging resistance due to the composition and thickness of the hydrophobizing coating layer. Increasing surfactant adsorption results in a switch between a Cassie-Baxter and a Wenzel regime for superhydrophobic surfaces at water-air. At oil-water interface wetting properties are strongly affected by the partitioning features of surfactants resulting in a switch between a Wenzel and a Cassie-Baxter regime. The presence of salts and the surfactant solution concentration is effective to decrease the contac angle and the effect of the roughness plays a role in maintaining a high hydrophobic effect. Conclusions The dependence of the wetting properties on different parameters like surfactant type and concentration show how the presence of amphiphiles is effective in lowering the contact angle in a hydrophobic or still superhydrophobic range. By coupling the adsorption properties and the repellence of the solid surface, the drop spreading can be controlled confining its volume in a restricted space. References Krasowska M., Ferrari M., Liggieri L., Malysa K. Influence of n-hexanol and n-octanol on wetting properties and air entrapment at superhydrophobic surfaces Phys. Chem. Chem. Phys., 2011, 13, 9452-9457. 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
