Structure and viscoelastic properties of hybrid ferrogels with iron oxide nanoparticles synthesized in situ

Ultra small angle X-ray scattering (USAXS) experiments in the q-range (10(-4)-0.2 angstrom) were performed to determine the structure of iron oxide NPs in situ synthesized inside semi-interpenetrating polymer networks (semi-IPNs) of linear alginate and crosslinked poly(N-isopropylacrylamide) (PNiPAAm). Results from the fitting of USAXS experiments were related with the reinforcement and swelling properties exhibited by the hybrid semi-IPNs which, in turn, were found to be highly dependant on the alginate concentration and the volume fraction of iron oxide nanoparticles. The USAXS findings, along with those from rheological and swelling measurements, allow determining whether iron oxide nanoparticles are bonded to the polymer matrix or if they are simply 'packed' inside the polymer network without interaction with the polymer chain.