Robust superhydrophobic aluminum surfaces

Despite the progress made on superhydrophobic (SHP) coatings, a key challenge is the ability to fabricate mechanically robust SHP surface. Scientists now report findings of the fabrication and characterisation of a mechanically robust SHP aluminum (Al) surface with enhanced corrosion resistance and reduced biofouling.

The new coating consists of a top hydrophobic layer of hexamethyldisilazane modified nano-silica (low surface energy material) and a middle connecting layer of hydrolysed glycidoxypropyltrimethoxysilane that is covalently bonded to the SHP surface and hydrophilic aluminum substrate. XPS analysis of the SHP coating confirms –O-Si-CH₃ groups. The SHP coating showed multi-scale fractal morphology with a fractal dimension of 2.2, and asperities of length scale 32 and 630 nm. The maximum water contact angle (WCA) of the SHP surface was 170 ± 1.5° with a sliding angle ~1°. The SHP surface showed good self-cleaning ability for both the hydrophobic and hydrophilic contaminant. Less than 5% detachment of coating after cross-hatch adhesion test (ASTM D3359-09) and the retention of superhydrophobicity up to 150 cm in the abrasion test (ASTM D4060), confirm the mechanical robustness of the fabricated superhydrophobic surface.

New insights

A two order reduction in the corrosion current density, and a corrosion inhibition efficiency of ~99% was observed in SHP surface compared to the bare sample. SHP sample showed poor adhesion to gram-negative and gram-positive bacterial strains and the superhydrophobicity was retained even after folding, shear abrasion test, cross-hatch tape adhesion test, and immersion in 0.1 M NaCl solution. Several new insights into the relationship between surface topography, fractal dimensions, self-cleaning process, anticorrosion and bacterial attachment were obtained.

The study has been published in Progress in Organic Coatings, Volume 162, January 2022.