Improvement of superhydrophobic coatings on aluminum surfaces by acid etching method using phosphoric acid

Abstract

Water repellency and self-cleaning properties are the most important characteristics for outdoor environment. The water contact angle (CA) of a surface is lower than 90◦, the surface is described as a hydrophilic surface. In addition, a surface is higher than 90◦, the surface is described as a hydrophobic surface. In superhydrophobic surfaces, CA is upper than 150 ͦ and the sliding angle (SA) is lower than 10 ͦ. They have attracted growing research attention, due to their important practical applications. In principle, superhydrophobic surfaces can be obtained by roughness of surface and reduction of surface tension. In this study, aluminum plates (5 cm x 2 cm x 1 cm) were polished with sandpaper. Then the plates were cleaned by sonication in acetone and ethanol. Afterwards, the cleaned aluminum surfaces were chemically etched by phosphoric acid (H3PO4) at different concentrations. Surface modification was done by dodecyltriethoxysilane at different concentrations and times. All these experiments were performed under atmospheric conditions. Finally coated samples were cured at 100 ͦC for 1 h. The morphology of the synthesized surfaces was characterized by scanning electron microscopy (SEM-EDX). The superhydrophobicity of the surfaces was determined by CA measurements. The best superhydrophobicity was obtained by acid etching method with %3 H3PO4 concentration and modification by 0,01 M dodecyltriethoxysilane for 1 h. As a result of CA measurements, maximum 156,83 ͦ value was obtained for coated aluminium surfaces. SEM image showed that the etched aluminum surface.