Preparation of hybrid composite microspheres containing nanosilicon via microsuspension polymerization

Hybrid composite microspheres with nano-Si as the core and poly(styrene-co-acrylonitrile) as a shell are successfully prepared by a two-step polymerization technique, which includes dispersion polymerization of styrene and 3-methacryloxypropyl trimethoxysilane in ethanol for surface modification of nano-Si followed by microsuspension polymerization of styrene and acrylonitrile in an aqueous phase for encapsulating nano-Si into an SAN copolymer matrix. The structure and surface properties of modified nano-Si are investigated by Fourier transform infrared spectroscopy (FTIR) and contact angle. The hybrid composite microspheres are systematically characterized by energy dispersive spectroscopy, thermogravimetric analysis, and transmission electron microscopy (TEM). According to the FTIR spectra and the contact angle experiments, it was determined that a hydrophobic polymer layer was formed on the surface of nano-Si. TEM showed that nano-Si was homogeneously dispersed in SAN particles when the loading capacity of nano-Si in the hybrid composite microspheres was less than 20 wt %. Moreover, scanning electron microscopy and X-ray photoelectron spectroscopy revealed that there were large amounts of nano-Si absorbed on the surface of the hybrid composite microspheres, and the mean particle size became much larger when the loading amounts of nano-Si reached 25 wt %. From this, it can be inferred that nano-Si overflows from the inner core to the outside surface in the emulsification process and acts as an inorganic dispersant.