Surface modification of titanium by electrochemical machining to control wettability.

Titanium and its alloys have vast applications in all forms of industry including the aerospace, automotive, aviation, and biomedical industries due to their low density, corrosion resistance, biocompatibility and high strength-to-weight ratio. Controlling the wettability, hydrophobic or hydrophilic nature, of metal surfaces extends their benefits to new realms such as anti-microbial, self-cleaning, anti-icing, and better osseointegration. The electrochemical surface modification (ECSM) method proposed in this study to control the wettability does not require the use of acid or base etching or chemical coatings, such as fluoroalkyl silane (FAS), and involves minimal harm to both environment and operators. Pure titanium surfaces were electrochemically modified in sodium chlorate electrolyte solution. The effects of processing time (5 – 20 mins) and voltage (5 – 20 V) were studied experimentally using a full factorial design. There was a notable difference in the wetting nature and surface appearance between the electrochemically modified titanium and unmodified titanium. After the sessile drop test on the modified titanium, the surface was found to be hydrophilic. On the contrary the unmodified titanium, the surface was found to be more hydrophobic. After drying in the furnace the electrochemically modified titanium had transitioned from hydrophilic to hydrophobic. The non-modified titanium had no change in wettability after being heat treated. The findings from the study suggest that the wettability of titanium surfaces can be controlled by using the ECSM method to achieve contact angles from a range of hydrophilic (< 90º) to hydrophobic (> 90º). The experiments also showed a positive correlation between processing time and voltage to the contact angles achieved after heat treatment.