Ultraviolet light-induced hydrophilicity effect on TiO2(110)(1 x 1). Dominant role of the photooxidation of adsorbed hydrocarbons causing wetting by water droplets.
ABSTRACT The UV photoproduction of a hydrophilic TiO(2)(110)(1x1) surface has been investigated in a pressurized ultrahigh vacuum apparatus under controlled conditions of hydrocarbon concentration in oxygen gas at 1 atm pressure. Water droplet contact angles have been measured continuously as the droplet is exposed to UV irradiation, yielding the first observations of a sudden wetting process during irradiation. Using hexane as a model hydrocarbon, it is found that when low partial pressures of hexane are present, the sudden onset of surface wetting occurs during UV irradiation after an induction period under photooxidation conditions. The induction period to reach the critical condition for sudden wetting increases when the partial pressure (and equilibrium surface coverage) of hexane is increased. These results indicate that the removal of adsorbed hydrocarbons by photooxidation is the critical factor leading to the UV-induced hydrophilicity phenomenon on TiO(2). The phenomenon does not occur in the absence of O(2) gas. A concept concerned with kinetic screening of the TiO(2)-H(2)O interface from O(2) by water droplets is presented to explain the observation of sudden wetting in our experiments, compared to gradual wetting which is observed following UV irradiation in all other experiments reported in the literature. Complementary infrared spectroscopy measurements of the effect of UV irradiation in an O(2) atmosphere on adsorbed Ti-OH groups and on adsorbed H(2)O on the surface of a high-area TiO(2) powder show that no spectroscopic changes occur. This indicates that UV-induced changes in the -OH coverage or the nature of -OH bonding to TiO(2), as suggested by others, cannot be used to explain the photoinduced hydrophilicity effect.
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ABSTRACT: To examine the effect of ultraviolet light (UV) treatment on the surface characteristics of two acid-etched zirconia-based dental implant materials.Methods Discs of two zirconia-based materials (Zr1 and Zr2) with smooth (m) and roughened (r) surfaces were treated by UV light for 15 min. The surface topography was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface elemental composition of all samples was determined by X-ray photoelectron spectroscopy (XPS), the crystalline property by X-ray diffraction (XRD) and the hydrophilic status by contact angle (CA) measurements of a water droplet.ResultsSEM and AFM revealed quantitative and qualitative differences between the roughened and smooth surfaces. UV treatment did not induce any topographic changes of the tested surfaces (p > 0.05). All UV-treated samples showed a significant surface elemental content change with a decrease of carbon by 43–81%, an increase of oxygen by 19–45%, and an increase of zirconia by 9–41%. Upon UV treatment, a 19–25% increase of the crystalline monoclinic phase was observed on surfaces of material Zr1, whereas a slight increase on the smooth Zr2 surface (+3%) and a decrease on the roughened Zr2 surface by 20% was observed. For all samples, the hydrophilic status changed significantly from hydrophobic to hydrophilic by UV treatment (p < 0.0001). The average contact angles were between 56.4° and 69° before and 2.5° and 14.1° after UV-light treatment.SignificanceUV treatment altered the physicochemical properties of the two zirconia implant surfaces investigated. The mechanism by which such changes are induced requires further investigation.Dental Materials 11/2014; 31(2). · 4.16 Impact Factor
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ABSTRACT: Previous models for the interface between titanium implants and biosystems take into account the oxide passivation layer and the hydroxylation, but omit the hydrocarbon contamination on air-exposed samples. The authors develop a consistent model for the contamination of the rutile (100) surface by small alcohols, which are known to be present in ambient atmosphere, and use this approach in molecular dynamics calculations. Contact angle evaluation reveals that hydrophobic surfaces can be generated. During molecular dynamics simulations with three peptides (RPRGFGMSRERQ, WFCLLGCDAGCW, and RKLPDA), polar side chains penetrate the hydrocarbons and become immobilized on the titanium dioxide. In the carbon layer, the peptide recognizes a hydrophobic environment, which was not present on the clean surface, and the authors attribute changes in the secondary structure in one case to this interaction. The authors further include the popular Matsui-Akaogi approach [M. Matsui and M. Akaogi, Mol. Simul. 6, 239 (1991)] into the frame of the AMBER force field and quote van der Waals parameters for fitting the original Buckingham part. With the new potential, the authors evaluated lattice parameters, thermal fluctuation, and bulk modulus. Translational diffusion coefficients and dipole autocorrelation functions of water on the surface are discussed in relation to surface properties, and it is shown that the water layers are more rigid than on earlier titanium dioxide models, and that contacts between peptide and surface are less direct.Biointerphases 09/2014; 9(3):031006. · 2.68 Impact Factor
- Dental Materials Journal 11/2014; · 0.94 Impact Factor