Multi-Stimuli-Responsive Polymer/Inorganic Janus Composite Nanoparticles

Multi-stimuli-responsive Janus composite nanoparticles (JNPs) of poly(N-isopropylacrylamide)–Fe3O4–poly(2-(dimethylamino)ethyl methacrylate)) (PNIPAM–Fe3O4–PDMEAMA) are synthesized by sequential reversible addition–fragmentation chain-transfer grafting of the polymer PNIPAM and atom-transfer radical polymerization grafting of the polymer PDMEAMA from the corresponding sides of modified Fe3O4 nanoparticles of ∼10 nm size. The hydrophilic/amphiphilic/hydrophobic reversible transition of the JNP can be triggered by pH and temperature since the wettability of the two polymers on the opposite sides is tunable accordingly. At a high pH value and a low surrounding temperature, applying near-infrared irradiation will induce the amphiphilic/hydrophobic transition owing to the photothermal effect of Fe3O4 NPs. The JNP can serve as a responsive solid emulsifier, and the stability and microstructure of the emulsions can be easily controlled by external stimuli such as the pH, temperature, and magnetic field.