Synthesis and swelling properties of poly(N-isopropylacrylamide)/nano-SiO2 composite hydrogels

The nano-composite hydrogels were prepared by the radical graft copolymerization of N-isopropylacrylamide onto the surface of nano-SiO2 particles treated with vinyltrimethoxysilane in a mixture solvent of H2O/THF at 25 degrees C and N,N'-methylene bisacrylamide (BIS) was used as the crosslinking agent. The products were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. These composite hydrogels exhibit higher swelling ratio than the usual poly( N-isopropylacrylamide) hydrogels at low temperature (15 degrees C) and more excellent water release behavior at high temperature (50 degrees C). The swelling ratio of hydrogel H1 which has no nano-SiO2 component, is about 29 at 15 degrees C, by contrast, the swelling ratio of hydrogel H4 which contents 5% nano SiO2 component is about 35 at the same temperature. At the same time, the water release behavior of hydrogel H4 shows an almost linear form, which is very essential to the controlled drug delivery systems. The reasons causing the property improvement of the hydrogels were discussed.