Synthesis and self-assembly of multiple-responsive magnetic nanogels

In this paper, temperature and pH-sensitive interpenetrating polymer network (IPN) nanogels (NGs) were firstly prepared, and magnetic hybrid NGs were made through in-situ precipitation of Fe2+ and Fe3+ into the IPN NGs. Under the optimized condition, the resulting hybrid NG dispersion with up to 17.3 wt% magnetite was stable, while the size distribution of the NGs is broad due to the formation of Fe3O4 nanoparticles outside the NGs. In order to synthesize relatively uniform magnetic NGs, magnetite content was reduced to 8.1 wt% magnetite. The NGs with 8.1 wt% magnetite can quickly self-assemble into colloidal crystals induced by magnet, while such NGs slowly self-assembled into colloidal crystals without external magnetic field. Furthermore, the reflection wavelength of the self-assembled magnetic NGs showed red-shift with increasing pH and temperature.