Grafting of trialkoxysilane on the surface of nanoparticles by conventional wet alcoholic and supercritical carbon dioxide deposition methods

The problem of lack of interfacial interaction between inorganic fillers and organic matrixes needs to be solved in order to obtain stable hybrid composites. Interfacial interaction can be improved by modifying the surface of inorganic fillers with organic bifunctional molecules. Surface modification was addressed in this work through silanization. High quality siloxane monolayers are not easy to form using the traditional solution-phase methodology, mainly because of the difficulty in controlling the amount of water in the liquid medium. This article reports an anhydrous and generic SCCO2 method for coating the surface of nanoparticulate materials through the deposition of self-assembled silane monolayers. The reaction of a trifunctional alkoxysilane with several micrometric, and nanometric substrates was study. Three different inorganic materials were chosen as substrates: micrometric and nanometric hydroxyapatite, nanometric titanium dioxide and layered hectorite. The silanization performance of the anhydrous supercritical method was compared to that of a conventional wet alcoholic solution method. Using the wet conventional method, silane deposition resulted in the deposition of polycondensed structures that cemented the inorganic nanoparticles. Since the supercritical method is an anhydrous method, monolayer formation of thermally stable coatings was favored and multilayer formation could be avoided by controlling the processing time. The supercritical process provided a very effective approach to functionalize individual inorganic nanoparticles because of the enhanced diffusivity of the functional molecules in the agglomerated interparticle voids. (C) 2005 Elsevier B.V. All rights reserved.