| Photonic crystals have recently been studied extensively because they offer unique ways of tailoring the propagation of light. A number of methods have been developed to create the periodic structures possessing photonic band gap (PBG). Some successes have been achieved through microfabrication techniques, but the pursuit of a microscopically ordered PBG in the visible range was still a challenging endeavor. Colloidal self-assembly has been utilized as a process to form 3D periodic structures because of its simplicity. A variety of methods have been explored to make photonic crystals materials from submicrometer balls of SiO2, polystyrene latex arranged into 3D ordered structures to porous, ceramic materials templated by this formed 3D ordered structures and oil emulsion. However, the resulting strain from shrinkage distorted the lattices and substantially degraded the optical properties of the colloidal crystals.The electrorheological (ER) or the magnetorheological (MR) effect offers a unique technique whereby the suspended particles can be self-assembled into body-centered-tetragonal (bet) mesocrystallites through the application of an external field [20,21].When ER and MR effects are combined, the network structures have been formed by X. P. Zhao et al. This provided a useful method to control the behavior of particles suspended in fluids.Three strategies of synthesizing composite particles responsive to electric and magnetic fields by combination of different coating techniques have been presented in the dissertation. And the assemblies of the prepared particles brought about the applied electric and magnetic fields were therefore examined. The first strategy is that the prepared Fe3O4/PSt magnetic polymer spheres were coated by amorphous titania, and Fe3O4/PSt/TiO2 composite particles were formed. The morphology and the structure of the particles were determined by SEM, FT-IR and TG-DTA. The resulting composite particles showed responses to both electric and magnetic fields by the reflection of forming into chains structures when a 0.6 kV/mm electric or 300 Gs/mm magnetic field strength was applied.The second strategy include that a metallic nickel (Ni) core was encapsulated with a polymeric polystyrene (PSt), and then coated with an outlayer of dielectric titania to form Ni/PSt/TiO2 composite particles. The morphology and structure of the particles were characterized by TEM, SEM, TG-DTA, XRD, and FT-IR. The resulting composite particles showed well responses to electric and magnetic fields, which was reflected by the formation of network structure under electric and magnetic fields superimposed perpendicularly.The third one is that the porous silica spheres are used as cores instead of solid silica beads, which give much less density. Then, the magnetic property is imparted by deposition of nickel by using electroless plating, while the dielectric property is offered by the outerlayer of titania. The morphology and structure of the particles were characterized by SEM, TEM, and XRD. The thermostability and sedimentation of the synthesized particles were also investigated. The resulting composite particles showed well responses to the electric and magnetic fields by the reflection of being ordered into chains structures under external electric or magnetic field, as well as formation of three-dimensional network under the adjusted electric and magnetic fields superimposed perpendicularly.Finally, the as-prepared composite particles size and morphology as well as their properties were summarized and compared in the dissertation. The synthesis of the composite particles responsive to electric and magnetic fields may provide a useful basis to control the behavior of the particles in suspensions.
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