Surface functionalization of radiopaque Ta2O5/SiO2

Mixed Ta2O5/SiO2 nanoparticles are attractive for their high radiopacity as transparent dental fillers and even for bone replacement. The effect of Ta2O5 content on surface acidity of flame-made Ta2O5/SiO2 particles was studied by NH3 temperature-programmed desorption (TPD). Emphasis was placed on the influence of particle composition on surface functionalization by a common surfactant, gamma-methacryloxypropyltrimethoxysilane (MPS). Such surface modified particles were analyzed by thermogravimetric analysis, C-13- and Si-29-NMR and FT-IR spectroscopy. Compared to pure silica, Ta2O5/SiO2 particles exhibited significantly higher surface acidity, thereby facilitating functionalization of their surface hydroxyl groups without a catalyst (e.g. n-propylamine, PA). The surface modifier structure was only slightly influenced by the Ta2O5 presence compared to pure SiO2. The long term hydrolytic stability of such surface modified Ta2O5/SiO2 particles was comparable to pure silica up to 80 days at 22 degrees C indicating stable bonding between particle surface and modifier. (C) 2007 Elsevier B.V. All rights reserved.