Article

Ultraviolet light-induced hydrophilicity effect on TiO2(110)(1x1). Dominant role of the photooxidation of adsorbed hydrocarbons causing wetting by water droplets

Surface Science Center, Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
The Journal of Physical Chemistry B (Impact Factor: 3.38). 09/2005; 109(32):15454-62. DOI: 10.1021/jp058101c
Source: PubMed

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.

0 Bookmarks
 · 
170 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultraviolet (UV) photofunctionalization has been shown to be highly effective at improving the osteoconductivity of titanium and TiO2 coated materials. We aimed to assess whether the bioactivity of TiO2 coated cobalt chromium molybdenum (CoCrMo) could be enhanced by UV photofunctionalization of the surface TiO2 layer. Using atmospheric pressure chemical vapour deposition (APCVD) a thin layer of anatase TiO2 was deposited onto smooth CoCrMo discs (referred to as CCMT). Human mesenchymal stem cells (MSCs) were cultured onto CCMT substrates which had been treated with UV light for 24 hours and identical substrates which had not undergone UV treatment. UV treated CCMT promoted a superior cell response in the form of enhancing markers of cell adhesion. This included stimulating the development of larger cells with increased levels of the adhesion protein vinculin and cytoskeletal protein f-actin (p < 0.05). In addition, MSCs were shown to have superior retention to UV treated CCMT after 3 and 24 hours (p < 0.05). Other cellular processes including proliferation, attachment, migration and differentiation were not affected by UV photofunctionalization. Despite this, the enhancement in cellular adhesion alone should result in an improvement in MSC retention to implant surfaces following surgery, and as a consequence, increase MSC resistance to dislodgement from external forces such as blood flow and micro motion.
    RSC Advances 01/2014; 4(104-104):59847-59857. DOI:10.1039/C4RA11524D · 3.71 Impact Factor
  • Source
    Dental Materials Journal 11/2014; · 0.94 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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). DOI:10.1016/j.dental.2014.10.008 · 4.16 Impact Factor

Tykhon Zubkov