Effect of CTAB on the architecture and hydrophobicity of electrodeposited Cu-ZrO2 nano-cone arrays

This study explores the hydrophobicity of micro and nano-hierarchical structured Cu-10 g/L ZrO2 pulse electrodeposits as a function of different concentrations (0.1, 0.5 and 1 g/L) of cetrimonium bromide (CTAB, a cationic surfactant) addition. Beyond 0.1 g/L CTAB loading, the composite coatings display duplex nano-cone morphology. Specifically, 0.5 g/L CTAB loaded coating shows free standing hemispherical morphologies consisting of vertically aligned nano-cone arrays, whereas 1 g/L CTAB loaded coating displays flowery like hierarchical nano-cone morphology. However, 0.1 g/L CTAB addition makes the coating morphology finer as compared to non-CTAB loaded coating with ordered nano-cone morphology. Among all the developed coatings, 0.5 and 1 g/L CTAB loaded coatings display superhydrophobic behavior by mimicking the 'lotus leaf' architecture. The entrapped air pockets formed beneath the liquid droplet due to the formation of micro and nanometer-scale topographic features mainly attribute to the transition from hydrophilic Cu substrate to super-hydrophobic Cu-ZrO2 hierarchical coating structure. In addition, high surface roughness along with the high value of the ratio between mean profile spacing (S-m) to mean profile width (W-a) facilitates the air entrapment in between the protrusions of the coated structure. Moreover, formation of low surface energy (111) crystal plane with respect to the CTAB loadings can be considered as another reason for the excellent hydrophobic behavior of the obtained Cu-ZrO2 coatings.