Composite particles polymer-coated silica

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

The adhesion of the polymer to the electrode surface is another consideration. For example, the polymer can be generated at an electrode such as tantalum, where it will not deposit. In our laboratories38 we have used the fact that deposition of PPy onto tantalum is difficult in the design of an electrochemical slurry cell to coat silica particles. The polymer generated at the tantalum anode does not deposit there instead, it deposits on the more receptive (silica particle) surfaces in the electrochemical cell. This represents a unique polymerization process whereby the polymer is generated electrochemically in an environment that allows nonconductive substrates to be coated, resulting in unique composite structures. 

Unlike the porous membrane, colloidal particles (such as PS or silica particle) are another type of template for the preparation of CPCs (Figure 11.10c). In previous work, core/shell PS/PANI composite particles were prepared by chemical oxidative seeded dispersion polymerization. A conventional coating protocol was employed as follows. The aniline monomer was dissolved in a strongly acidic solution in the presence of the PS seed latex (an alternative method involves using a miscible aniline hydrochloride monomer without external acid). Then polymerization was initiated by the addition of oxidant aqueous solution. The suspended PS particles were coated with PANI by in situ deposition of the formed conducting polymer or oligomer from the aqueous phase. 

Numerous researches have been conducted to modify abrasive particles for scratch reduction. Mixed abrasive slurry and various dispersants were used for the development of hne slurries [44,45] slurries made of abrasives with soft polymer coating are also proposed [46] polymer-core silica-shell composite abrasives were reported too [47]. However, most of these modified/composite abrasive slurries remain experimental and have not received wide industrial acceptance yet, because of challenges in particle control and difficulty in cleaning the residual abrasives. 

As a result of the advances in catalyst discovery for aqueous ethylene polymerization, silica-polyethylene nancomposites have been prepared with structures that vary with changing catalyst structure and silica composition." It is likely that many more advances in the area of high-tech composites with potential biological and nanotechnology applications will be made in the next few years through aqueous polymerization processes. In addition to free radical polymerizations and catalytic polymerizations, it should be noted that oxidative polymerizations can also be performed in aqueous media to yield conducting polymers. Recently, this has been used to prepare polypyrrole-coated latex particles that are expected to be interesting synthetic mimics for micrometeorites. 

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