Superhydrophobicity on aluminum through reactive-etching and TEOS/GPTMS/nano-Al2O3 silane-based nanocomposite coating

The aim of this work was achieving of superhydrophobicity on aluminum based on nano/micro hierarchical surface structure through chemical etching and subsequent coating. Hence, the micro-scale roughness was obtained by an ultrafast chemical reactive-etching of Al by CuCl2, and nano-scale roughness was obtained by nanoparticles decorating via a silane-based nanocomposite coating, which acts not only as a supporting matrix for nanoparticles but also acts as a protective layer. By functionalization using a fluoroalkylsilane (FAS) solution, the superhydrophobic nano/micro hierarchical surface structure was achieved with the water contact angle (WCA) and water contact angle hysteresis (WCAH) of 164 degrees and 2.5 degrees, respectively. The silane-based layer has been prepared by sol-gel method using a hybrid of Tetraethylorthosilicate (TEOS), and 3Glycidyloxypropyltrimethoxysilane (GPTMS) and the nanocomposite layer has prepared by addition of Al2O3 nanoparticles. The effect of functionalization of Al2O3 nanoparticles to prepare the highly dispersed nanoparticles within the silane layer has been investigated in details. The surface morphology was characterized by atomic force microscopy (AFM) as well as scanning electron microscopy (SEM), and the chemical bonding state was explored by Fourier transform infrared spectroscopy (FTIR). The robustness of hydrophobicity of the samples was analyzed by sandpaper abrasion test as well as corrosion mitigation evaluation using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The appropriate equivalent circuit model was asserted to analyze the EIS data, quantitatively. The results revealed that the incorporation of functionalized Al2O3 nanoparticles within the silane layer was able to create stable nano/micro hierarchical surface structure leading to the superhydrophobicity along with higher corrosion mitigation performance in comparison to the pure silane layer.