Preparation And Characterization Of Silica-Polyacrylonitrile Core-Shell Composite Nanospheres

Carbon nanospheres(CNSs)are emerging as a new kind of carbon materials with great development and application potentials due to their outstanding physical and chemical properties,including chemical stability,thermal stability,excellent electrical conductivity and thermal conductivity and so on.Chemical vapor deposition,solvothermal,and template method can be used to prepare carbon nanospheres of various structures.However,it is very difficult to accurately control the size of carbon nanospheres and thus prepare mono-dispersed carbon nanospheres of high purity and size uniformity.It is an efficient way to obtain carbon nanospheres via thermal treatment of polymeric nanospheres precursors with controlled structure,size and morphology.In this paper,silica nanoparticles and acrylonitrile were used to prepare silica-polyacrylonitrile composite nanospheres via emulsion polymerization method.The influences of various reaction parameters on the particle size and morphology of SiO2-PAN composite nanospheres were studied.Silica nanoparticles were first prepared by alkaline hydrolysis of tetraethyl orthosilicate(TEOS)in ethanol solution.The influence of the concentrations of ammonia,water and TEOS on the size of SiO2 nanoparticles was investigated.The results showed that the size of silica nanoparticles increased with increasing concentration of ammonia,water or TEOS.In order to strengthen the interaction of SiO2 nanoparticles and PAN,3-(trimethoxysilyl)propyl methacrylate was used to modify silica nanoparticles,and double bonds were introducted to the surface of silica nanoparticles.Dynamic light scattering(DLS),Fourier transform infrared spectroscopy(FT-IR),elemental analysis and field emission scanning electron microscopy(FESEM)were used to characterize the size and size distribution,chemical composition and morphology of SiO2 nanoparticles before and after modification..Narrowly-distributed silica-polyacrylonitrile core-shell composite nanospheres were prepared via emulsion polymerization using MPS-modified silica nanoparticles as the seeds.DLS,FT-IR,TEM and FESEM were used to characterize the size,composition,structure and morphology of various nanospheres.The effects of the surface modification of nano SiO2 seeds,the concentration of nano SiO2 seeds,the type of initiators,the feeding mode and concentration of surfactant,the reaction temperature and the introduction of crosslinker on the synthesis of the composite nanospheres were investigated.Results showed that the surface modification of SiO2 nanoparticles can lead to the good combination of SiO2 nanoparticles with PAN and the successful preparation of SiO2-PAN composite nanospheres..When the initial surfactant amount increases,the supplement rate of surfactants increases,or the reaction temperature decreases,the size of SiO2-PAN composite nanospheres decreases.SiO2-PAN composite nanospheres with relatively smooth surfaces can be obtained via reducing the reaction temperature or introducing crosslinker.SiO2-PAN composite nanospheres can also be successfully prepared at a nano SiO2 seed concentration as high as 4wt%.Three-layered core-shell SiO2-PAN-PMMA composite nanospheres were prepared via emulsion polymerization using SiO2-PAN nanospheres as the seeds.The conditions of pre-oxidation and carbonization were investigated preliminarily.Results showed that the PMMA shell can protect the SiO2-PAN core during pre-oxidation and carbonization.The final product was carbon nanospheres with core-shell structure.However,sintering reunion still existed in the carbon nanospheres.