|dc.description.abstract||Two methods are reported herein to render titanium metal superhydrophobic. A superhydrophobic surface by definition is one that shows a water contact angle of equal to or greater than 150˚,(1) while in contrast bare titanium metal is hydrophilic and exhibits a water contact angle of 73±3˚.(2) Titanium metal is extremely reactive in air and rapidly forms a self-repairing oxide layer, which makes the necessary surface modification of the material to render it superhydrophobic challenging.
The first method employed in this work consists of a cold compression procedure whereby copper powder that has been previously rendered superhydrophobic by galvanic deposition of silver followed by treatment with 1-dodecanethiol is compressed onto titanium powder. The resulting compact consists of a superhydrophobic copper layer on a titanium substrate. The superhydrophobic copper layer is robust in that if it is damaged, the damaged layer can be abraded away to expose a new, fresh superhydrophobic copper layer beneath. Each successive layer exposed after abrasion throughout the superhydrophobic copper portion of the material is shown to exhibit the same wetting characteristics with regards to water roll-off angle.
The superhydrophobic titanium material prepared by this method exhibited a static water contact angle of 157±1º and water roll-off angles of 3.8±0.9º. The method was also successfully applied to aluminium powder, which showed a water roll-off angle of 4.2±0.4˚.
An additional superhydrophobic titanium material was prepared using this method which had a polyfluoroalkylthiol surface modifier, 1H,1H,2H,2H-perfluorodecanethiol, used in place of the 1-dodecanethiol. This material showed no statistically significant difference in wetting behaviour from its alkylthiol treated counterpart, with a water roll-off angle of 3.4±0.5˚ and a static water contact angle of 159±3˚.
The second method employed in this work was applicable to a foil form of titanium. It involves the deposition of copper onto a titanium foil, followed by galvanic reduction of silver onto the copper plate and adsorption of 1H,1H,2H,2H-perfluorodecanethiol in a self-assembled monolayer. Difficulty was encountered in getting a reproducibly adherent copper plate onto the titanium foil, and two methods were experimented with to find optimum conditions for an adherent copper deposit.
The first strategy used to deposit copper onto titanium involved a high voltage capacitor discharge across a titanium electrode in an acidic copper sulfate solution to destroy the native oxide layer present on titanium. A copper electroplate immediately followed this step, though unfortunately none of the deposits prepared in this manner passed adherence tests. The second method involved an anodic etching step before deposition of copper and showed much improved adherence over the first method, but was inconsistent and the copper coatings were non-uniform.
The superhydrophobic titanium materials prepared on titanium foils using both methods of copper deposition showed the same roll-off angles for an applied glycerol droplet as a purely superhydrophobic copper foil. A previous publication1 has quoted superhydrophobic copper foil prepared by the same method as having a water contact angle of 173±1˚ and a water roll-off angle of 0.64±0.04˚. Extrapolating from the materials sharing the same glycerol roll-off angles gives some confirmation that a superhydrophobic surface has successfully been applied to titanium foil in this work.||