Preparation of Hybrid Nanocomposites by the Sol-Gel Method

Other modifications of this method for the preparation of nanoparticles in polymers have been reported. In one modification, catalysts containing highly dispersed transition metals particles immobilized in films were obtained by the electrolytic oxidative polymerization. A monomer derived from mercaptohydroquinone was electropolymerized in the presence of platimun group metals. These metals were incorporated by electrochemical deposition.  

Not all of the approaches discussed in this section are equally developed. The priority is given to the reduction techniques. The role of the dispersive phase is mostly played by carbon-chain polymers and less often, by condensation-type polymers. The immobilization of nanoparticles is nearly always accompanied by chemical interactions of the particles formed with the matrix, in contrast to mechanical mixtures of metals with polymers. Further developments in the preparation of polymer-immobilized nanoparticles have been documented. 

In this method, hydrolysis and condensation are catalyzed by the same com-poxmd (by acid, base or, sometimes, by a nucleophilic catalyst, such as NaF). These reactions with Si(OR)4 have long been known. Apparently, the preparation of monodisperse Ti02 particles by hydrolysis of alkoxides was described first by Barringer and Bowen. 

Addition of complex 1 and removal of free and latent water by condesation  

The metal alkoxides affect substantially these reactions. Thus Ti(OPr )4 and OV(OPr )3, cocondensates act as catalysts in transesterification of tetramethoxy- and tetraethoxysilanes (TMOS and TEOS, respectively) during sol-gel nanocomposite preparation.  

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The sol-gel method was widely used in the preparation of photonic materials and structures during the last decades. The design and preparation of hybrid nanocomposites for photonics are widely described in Refs [7,145-147]. The wide range of photonic structures prepared using the sol-gel method include colloidal crystals based on silica or polystyrene spherical particles [148,149], photonic crystals [150-152], photonic bandgap materials [153-155], and opals based on the deposition of silica, titania, and/or ceria in the voids of an ordered array of PMMA spheres [156]. A more extensive overview of photonic materials by sol-gel method can be found in Chapter 28. 

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