Thermoresponsive poly(N-isopropylacrylamide) nanogels/poly(acrylamide) nanostructured hydrogels

Here we report the preparation and characterization of nanostructured thermo-responsive poly (acrylamide) (PAM)-based hydrogels. The addition of slightly crosslinked poly(N-isopropylacrylamide) (PNIPA) nanogels to AM reactive aqueous solution produces nanostructured hydrogels that exhibit a volume phase transition temperature (T-VPT). Their swelling kinetics, T-VPT's and mechanical properties at the equilibrium-swollen state (H-eq) are investigated as a function of the concentration of PNIPA nanogels in the nanostructured hydrogels. Nanostructured hydrogels with PNIPA nanogels/AM mass ratios of 20/80 and above exhibit higher H-eq and longer time to reach the equilibrium swelling than those of the conventional PAM hydrogels. However, the PNIPA nanogels possess thermo-responsive character missing in conventional PAM hydrogels. The T-VPT of nanostructured hydrogels depends on PNIPA nanogel content but their elastic and Young moduli are larger than those of conventional hydrogels at similar swelling ratios. Swelling kinetics, T-VPT, and mechanical properties are explained in terms of the controlled inhomogeneities introduced by the PNIPA nanogels during the polymerization.