Rheological behaviors and secondary networks of polyacrylamide hydrogel filled with silica

Polyacrylamide (PAM) hydrogel filled with different types and contents of hydrophilic silica was synthesized by in situ polymerization. Rheological behaviors of the hydrogels were measured with an oscillation rheometer. The results indicated that the addition of silica efficiently improved the mechanical properties of the hydrogel, both for the uncrosslinked system and crosslinked system; simultaneously, the storage modulus (G′), loss tangent (tanδ) and viscosity (η) of the hydrogel were obtained. These results suggest that a nonbonded complexation existed between the silica and the molecular chains of PAM that endowed the hydrogel with special behaviors. Results from Fourier Transform infrared spectroscopy (FTIR) showed that the action of the nonbonded complexation was derived from hydrogen bonds between hydroxyl groups of silica and amide groups of PAM. The formed secondary networks endowed the hydrogels with high mechanical properties.