Studies On The Preparation Of Composite Microspheres With Hierarchical Surface Morphologies Based On PAM Porous Microspheres As Templates

Recently, template method on preparation of composite materials with special structure and properties has become the focus of active research. The template method is superior to other approaches, in which the size, structure and morphology of the prepared materials can be controlled and adjusted by simple altering the nature of template and the preparation conditions. Moreover, template can be predesigned in the size and shape of objective materials.Polymer microgels are microsphere materials with similar structures of bulk gels. The three-dimentional network structure appears in rich solvent, and then porous microgles with unusual surface morphologies after treatment of microgles can be obtained. Additionally, the organic-inorganic composite microspheres with hierarchical surface morphologies can be feasibly gained using the controllable porous microgels as template. Based on the idea mentioned above, the research in this thesis includes the following parts.(1) The polylacrylamide (PAM) microgels are prepared by inverse suspension polymerization method, and porous PAM microgels are prepared by the freeze-drying treatment of the swollen microgels. The different surface morphology of porous PAM microgels can be obtained by adjusting the content of cross-linker-N, N'-methylene bisacryamide (BA) in microgels. The surface morphology of porous microgels can be controlled in the swollen degree of microgels and the content of cross-linker in microgels. SEM and X-ray diffraction measurements are empolyed to monitor the porous surface structures and the crystallographic state. The research results show that the surface morphology in the pore size and pore volume regularly change with the content of cross-linker, and the microgels are amorphous. The results of BET and mercury injection method analysis indicate that the pore size in the porous microgels are commonly divided into macropores (the pore size＞50 nm), and micropores (the pore size＜2 nm). Based on these results, a novel approach for preparation organic-inorganic composite microspheres with porous structure surface morphology could be set up.(2) Utilizing the porous PAM microgels as templates, PAM/TiO₂ composite microsheres with hierarchical surface morphologies are prepared by in situ hydrolysis and condensation of tetrabutyl titanate located at the templates in a moist atmosphere. The morphology and constitute of composite microspheres are characterized by SEM,FT-IR,TGA,XRD,Brunauer-Enmet-Teller and mercury injection method analysis, respectively. The results indicate that the composite microspheres with different hierarchical surface morphologies could be obtained by controlling the cross-linking degree of the porous PAM microgels, the relative humidity of the gas phase, the amount of residual impregnation liquid and the TBOT concentration in the porous PAM microgels. Although the surface morphologies of the composite microspheres are varied, the morphologies are typically divided into three categories: (1) wrinkled surfaces covered with large dense TiO₂ particles; (2) porous structures sparsely suffused with large TiO₂ particles along the fringes and inner walls of the porous channels; (3) macroporous surfaces with small TiO₂ particles distributed ubiquitously. The incorporation of TiO₂ particles into PAM microgels resulted in an obvious increase in specific surface area, and the pore size distribution of the microspheres depended strongly on the size of TiO₂ particles.(3) Based on the porous PAM microgels as template, the porous structure PAM/Ag composites microspheres are prepared by in situ reduction of silver nitrate by hydrazine hydrate in a closed container at room temperature. The SEM results show that the composite materials with different surface morphologies and porous structure can be obtained by changing the reaction conditions. According to the results, the pore parameter and specific area of the composite materials can be effective adjusted. Additionally, Ag particles loaded on the composite microspheres are homogeneously distributed. XRD spectra demonstrate that the composite material is amorphous. The PAM/Ag composite material has a potential application in catalysis and adsorption due to the property of Ag and the regular porous structure.