Novel Fabrication of Un-coated Super-hydrophobic Aluminum via Pulsed Electrochemical Surface Modification

Super-hydrophobic and super-hydrophilic aluminum (Al) surfaces were fabricated via electrochemical surface modification (ECSM) in neutral NaClO3 electrolyte without the addition of secondary chemical coatings. The effects of processing time and applied potential on the surface roughness and wettability were studied. The aluminum surface was characterized using stylus profilometer and scanning electron microscope (SEM). Wettability was evaluated using Sessile Drop Test and a high resolution camera. Results show that surfaces obtained hierarchical rough features and super-hydrophilic behavior after pulse electrochemical machining. Heat treatment at 200 °C transitioned the substrates to exhibit super-hydrophobic behavior due to the removal of all moisture from within the micro- and nano-meter scale features on the aluminum surfaces, allowing for the reformation of a natural passivation (oxide) layer with atmospheric interaction. The method proposed in this study for producing super-hydrophobic aluminum surfaces does not require the use of acid or base etching or chemical coatings, such as flouroalkylsilane (FAS). Experimental results reveal increase in contact angle, with increase in applied potential, and decrease in sliding angle.