Spontaneously formed nanostructures on titanium surfaces

The aim was to investigate the evolution of nanostructures on the SLActive surface, as a function of time, storage conditions, material dependence and to identify the step in which the reorganization of the outermost titanium oxide layer into well defined nanostructures takes place.

Titanium grade 2 discs were surface modified in seven different modes; (1) SLA (sand blasted, large grit, acid etched) protocol. (2) SLActive protocol (SLA stored in 0.9% NaCl solution), (3) SLActive, but stored in water instead of 0.9% NaCl solution, (4) pmod SLA: SLA discs subjected to oxygen plasma cleaning and stored in 0.9% NaCl solution, (5) SLAnano: SLActive discs aged for several months and then dried, (6) Mod A: same etching procedure and storage as for SLActive, but no sand blasting prior to etching, (7) pmod P: the discs were polished, oxygen plasma cleaned and stored in 0.9% NaCl solution. In addition TiZr alloy discs were prepared like the Ti SLActive samples. The surfaces were evaluated with SEM, interferometry, contact angle measurements and XPS.

The samples stored dry were hydrophobic whereas the discs stored in liquid were hydrophilic. The evolution of nanostructures took 2 weeks, thereafter they were stable over time. The nanostructures occured after storage both in water and NaCl solution. Nanostructures were formed on Ti and TiZr although the morphology and distribution was quite different between the two materials.

Acid etching in conjunction with storage in aqueous solution is responsible for the reorganization of the outermost titanium oxide layer into well defined nanostructures.