Molecular Dynamics and Macroscopic Properties of Magnetic Microgels

Abstract

Thermo-sensitive microgels based on poly(N-isopropyl acrylamide) (PNIPAM) were covered with nanoparticles of γ-Fe2O3 with size around 6 nm. When the inorganic cover was 18% (w/w) respect the polymer part, the microgels presented magnetic properties in addition to their inherent thermo-sensitivity. The interactions existing between the magnetic nanoparticles and the polymer matrix provoke the shifting of the microgel volume transition to higher temperatures when the amount of γ-Fe2O3 increases. The study performed using incoherent quasielastic neutron scattering (IQNS) confirms that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both, the mean square displacement of the polymer segments and the diffusive motion of the polymer chains, decrease as the iron oxide content increases. The reduction of vibrational and diffusional motions of the polymer chains is attributed to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles that explains the reduction of the swelling capacity of the microgels and the shift of the polymer volume transition to higher temperatures with increasing the iron content.