Stimuli-responsive magnetite nanoparticle monolayers

The stimuli-responsive behavior of copolymer-capped NPs (Fe 3O4@MEO2MA90-co-OEGMA10 and Fe3O4@MEO2MA) was studied in the temperature interval between 6 and 43 °C at the air/water interface, and at 20 and 37 °C on the surface of 150 mM NaCl, 1 M NaCl, and 2% citric acid aqueous solutions. The critical surface pressure of the NP layers and the exchange of the NPs between the interface and the subphase respond clearly to temperature and ionic strength changes of the aqueous subphase. The comparative study of the two NP systems allowed the determination of the influence of the oligo(ethylene glycol) methacrylate (OEGMA) moiety on the stimuli-responsive interfacial behavior. The conformational change of the copolymer seems to dictate the interfacial behavior of the copolymer-capped NPs below and above their characteristic LCST (lower critical solution temperature).