TiO2 nanotubes from stirred glycerol/NH4F electrolyte: Roughness, wetting behavior and adhesion for implant applications

Titanium oxide (TiO2) was anodically formed on titanium from non-aqueous electrolyte containing glycerol and 0.5 wt.% ammonium fluoride (NH4F). Oxidation was carried out for 30, 60, 120 and 240 min at potentiostatic 30 V with the bath being stirred using magnetic pellet. All the conditions produced amorphous nanotubes. They had an average diameter of 50–130 nm and length in the range of 1.2–1.9 μm. The porosity was in the range of 70–80%. Stirring of the glycerol-based electrolyte has proved to be advantageous in retaining the tubular structure and providing smooth tubes even at 30 V condition. The coatings had surface roughness Ra lower than 0.5 μm, water wetting angles in the range of 58–84°. Increasing pore diameters increased the water wetting angles. All the coatings invariably showed poor tensile pull-off adhesion strengths. This poor adhesion is attributed to the stirring of the electrolyte.