The effect of superhydrophobic surface topography on underwater corrosion resistance of steel

This article describes the study of the topography effect of superhydrophobic surfaces on the corrosion protection performance of steel through the air plastron behavior when subjected to an underwater environment. A random superhydrophobic surface was fabricated using spray coating and characterized for morphology and wettability by scanning electron microscopy (SEM) and goniometer measurements, respectively. By comparing the coated surfaces both with and without air plastron, it was found that superhydrophobicity postponed the corrosion of the coated steel specimens. This increase in corrosion protection of the superhydrophobic surface was due to the air plastron created by the superhydrophobicity in underwater immersion. Since different areas showed differing air plastron lifetimes (wetting behavior), it was assumed that the underlying topography of the superhydrophobic coating controlled the air plastron lifetime. To investigate this behavior, the micron scale topography of the different areas was studied using the technique of laser confocal microscopy over the specific areas and correlating with air plastron lifetime. Using the theoretical analysis based on superhydrophobic robustness and assuming the solid fraction is the same for different locations, it was demonstrated that the feature size [extracted by roughness analysis as root-mean-square (RMS)] correlated with the air plastron lifetime. It was confirmed from the plot of RMS and air plastron lifetime that smaller feature sizes could extend the air plastron lifetime and provide better anticorrosion performance.