Hydrophobic as well as superhydrophobic surfaces are attracting a multitude of applications owing to their self-cleaning capacity and ability to provide surfaces with enhanced corrosion behavior. Several studies have indicated that it is possible to come up with more hydrophobic surfaces by adopting natural surface patterns. This can be realized through templating, lithography or plasma treatment.
Unfortunately, a number of these surfaces do not exhibit aesthetic appearance. Sol-gel approach has been identified to pave way for the fabrication of transparent coatings with low surface energy. Despite the huge efforts put in the fabrication of such surfaces, there is still the need to understand the superhydrophobicity phenomenon as well as the resulting attributes. A number of properties of these transparent coatings are yet to be explored in a bid to overcome poor ware strength, limited optical transparency and their costly and complex fabrication methods.
Mariola Pantoja and colleagues at the Universidad Carlos III de Madrid in Spain investigated the role of the various components of the solution composed of nanoparticles, silanes, and solvent and evaluated their capacity to develop a superhydrophobic coating. They also evaluated the potential relationship between the solvent properties and its potential to yield hydrophobicity. Their work is published in peer-reviewed journal, Applied Surface Science.
The authors coated stainless steel plates with silane solutions. In a bid to understand the outcomes of the experiment, the researchers prepared the coatings from three solutions. The first solution contained the solvent with silicon oxide nanoparticles only, the second contained silane with the solvent only, and the third contained a solvent with both silicon oxide and silane.
The authors then conducted contact angle and surface morphology measurements of the coated surfaces. They evaluated the aesthetic appearance of the coated surface by visual inspection, specular gloss, and colorimetric measurements.
They observed that only coatings fabricated from silicon oxide-silane solution for the white spirit solvent indicated superhydrophobic characteristics. White spirit was marked as the only solvent with sufficient capacity to disperse hydrophobic silicon oxide particles. The degree of dispersion on these nanoparticles was a function of the solvent selected. Solvent with higher dispersive components exhibited higher degrees of dispersion of the hydrophobic particles. Moreover, the hydrolysis of silane molecules was only observed for solutions synthesized from non-anhydrous solvents. Therefore, to fabricate hydrophobic surfaces, the authors started from a solution with less ability to hydrolyze alkoxy to silanol groups and higher ability to disperse nanoparticles.
There existed a synergetic effect between silicon oxide and the silane mix in the presence of the white spirit solvent, and this led to the formation of superhydrophobic coating. The hydrophobic attributes were due to the mixing nano and micro-structured roughness provided by particles, and hydrophobicity offered by silanes.
The research showed that the superhydrophobic coatings generated from the silane-silicon oxide solution in the presence of white spirit solvent were transparent by visual inspection. Color as well as gloss measurements indicated a loss of lightness and gloss when silicon oxide was used to fabricate the coating. Small color differences, lower than 5 , were found.
These transparent, hydrophobic coatings can be used in different materials used in construction as well as in creative architecture to enhance their surface properties, as KrEaTive Habitat project (financed by Interreg SUDOE, Ref. SOE1/P1/E0307) is focusing on.
M. Pantoja, J. Abenojar, and M.A. Martinez. Influence of the type of solvent on the development of super hydrophobicity from silane-based solution containing nanoparticles. Applied Surface Science, volume 397 (2017), pages 87–94.Go To Applied Surface Science