Experimental and computational insights into self-assembly sodium oleate on anodized aluminum interface in electric field

Electrochemical etching method has been used to construct anode aluminum foils with large surface area for electrolytic capacitor application. The applied current concentrated on surface defects would cause excessive corrosion of aluminum substrate and accelerate the initiation of merged tunnels. Self-assembly treatment with sodium oleate presents considerable improvement on optimization of size and structure of etched tunnels. Experimentally, aluminum foils with high etched tunnel density nearly 1.5027 × 10⁷ cm⁻² could be prepared after 0.10 mmol L⁻¹ sodium oleate treatment. Theoretically, molecular dynamic and quantum chemistry calculations reveal the self-assembly process of sodium oleate in forms of oleic acid on Al (100) facet. The results indicate that the oleic acid monolayer will form at molecular density nearly 0.855, 0.847 and 0.844 mol. nm⁻² as electric field E equal 0, 0.10 V Å⁻¹ and 1.00 V Å⁻¹, respectively. Based on the calculations of surface coverage in electric field conditions, experimental adsorption isotherm has been corrected to determine the optimal concentration of self-assembly composition.