Synthesis and characterization of acrylic acid-based SiO2 nanocomposite hydrogels

Acrylic acid (AA) nanocomposite hydrogels (NCH) containing different kinds of SiO₂ nanoparticles were prepared by way of free radical polymerization. The polymerization conditions were optimized considering the initiator and monomer concentrations in the mixture, as well as the reaction temperature and time. SiO₂ nanoparticles were used in original (neutral), NH₂ modified (hydrophilic) and perlite forms. Nanocomposite hydrogels that contain NH₂ modified nano-SiO₂ were found to present swelling values higher than those of the original acrylic acid nanocomposite hydrogel and the nanocomposite hydrogel that contain original SiO₂. AA-perlite nanocomposite hydrogels were used to achieve the best thermal stability, although the perlite-doped hydrogels exhibit less swelling due to the large particle size of perlite and its lower SiO₂ content. FESEM and mapping analyses were conducted to verify the incorporation of SiO₂ nanoparticles into the hydrogel structure. Amorphous structures were determined by an XRD analysis. Thermal stability of hydrogels was measured by TG-DTA. The thermal stabilities of NH₂-modified SiO₂- and perlite-doped nanocomposite hydrogels were found to be higher than those of plain hydrogel and original SiO₂-doped nanocomposite hydrogels.