| Composite particles are the particles which are made up of two or more different particles. The inorganic/organic composite particles are prepared by combining the inorganic and organic phases in nanometer to submicron not by the simple admixture of them. Composite particles often exhibit improved composite synergies over their single-component counterparts. The preparation of nanoscale inorganic particles/polymer composite particles not only can reduce the aggregation of nanoscale particles, more importantly, the characteristic and functional design of the product surface can be achieved. It also makes the products have some special performances or multifunctional properties, so that to prepare a novel composite function material. The inorganic particle/polymer composite particles are widely used in the coatings, plastics, rubbers, ceramics, cosmetics, drugs, and so on.Based on the investigation of nano-TiO2 dispersibility, three different polarity polymers and nano-TiO2 systems are selected for investigating the basic problems of emulsion polymerization used for polymer encapsulation of nano-TiO2 in the paper. The main conclusions are as follows:1. Nano-TiO2 was prepared by direct hydrolysis of titanous sulfate under boiling reflux conditions and characterizied by TEM, SEM, XRD, IR and DTG. The dispersibility and dispersion stability of the particles were investigated using transmittances and TEM observation. The results showed that the TiO2 suspension with a good dispersion stability could be achieved through ultrasonic irradiation, by adding inorganic dispersant or surfactant or controlling the medium pH.2. The nanocomposite particles of TiO2/PSt, TiO2/P(St-MAA), TiO2/P(MMA-BA-MAA) were prepared by emulsion polymerization. The composite particles with smooth surface, good dispersibility and spherical core-shell structure could be prepared by selecting adequate surfactant concentration and monomer concentration ratio at a certain temperature.3. The kinetics study of the reaction showed that the coating polymerization rate was influenced by the surfactant concentration, the amount of initiator, monomer dosage, the reaction temperature, and so on. The whole reaction of coating polymerization for TiO2/PSt system, the rate equation was R= k [E]0.68[I]2.2[M]1.61 and the apparent activation energy was 72.7 kJ-mol-1. TiO2/P(St-MAA) system, that was R=k[E]0.53[I]0.90[M]R 0.76 and the apparent activation energy was 83.0 kJ-mol-1. TiO2/P(MMA-BA-MAA) system, that was R=k[E]1.66[I]0.93[M]R 1.4[T]0.65 and the apparent activation energy was 163.0 kJ·mol-1.4. The IR spectra showed that the nano-TiO2 particles were coated with the polymers. Thermal analysis showed that the thermal stability of composite particles was higher than that of polymer particles formed under the same conditions, the differences of the original decomposition temperature between them were about 30～60℃. According the data, the percentage of polymers in composite particles and the encapsulation efficiencies could be estimated.5.ζ-potential measurements showed that there was no zero potential point of the composite particles within pH= 2～12. Compared with nano-TiO2, the contact angles of composite particles indicated that the hydrophilic of composite particles decreased and the lipophilic nature increased. The transmittance experiment indicated that the composite particles showed good dispersibility in organic solvent.6. Based on the experimental results, the reaction mechanisms of encapsulation were conjectured to be so-called TiO2/Surfactants"micelles"nucleation that the"micelles"were formed by surfactants absorbed onto the nano-TiO2 surfaces and homogeneous coagulative nucleation which happened when the radicals produced from initiators went up to a certain size in the water phase. The TiO2/Surfactants"micelles"nucleation was dominant in TiO2/PSt system. There were homogeneous coagulative nucleation as well as TiO2/Surfactants"micelles"nucleation in TiO2/P(St-MAA) and TiO2/P(MMA-BA-MAA) systems.
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