We report a simple synthesis technique to attached poly(N-isopropylacrylamide) on magnetic nanoparticles. Fe3O4 magnetic nanoparticles were prepared using co-precipitation method. Nearly monodisperse nanoparticles were separated by terminating surface of Fe3O4 with dopamine followed by careful centrifugation and decantation. NHS/EDC coupling chemistry was employed to attached the carboxylic acid terminated poly(N-isopropylacrylamide) to amine end of dopamine on surface of the magnetic particles. Analysis of the polymer brush layers was conducted using UV-Vis spectroscopy, ATR−FTIR, and Transmission electron microscopy techniques. The magnetic property was investigated using direct current superconducting quantum interference device (DC-SQUID) method.

Temperature-sensitive ferrogel prepared using Fe3O4 nanoparticles are characterized under varying temperature conditions. The nanoparticles were distributed in Nisopropylacrylamide (NIPAm) during their polymerization to form hydrogel. Particle distribution and agglomeration characteristics of the prepared ferrogels were investigated using ultra small angle x-ray scattering (USAXS) at various temperatures through the Lower Critical Solution Temperature (LCST). Transmission electron microscopy (TEM) was used to estimate the particle size distribution. The magnetic property was investigated using direct current superconducting quantum interference device (DC-SQUID) under hydrated conditions. The USAXS analysis showed an increase in the volume of particles without changing the agglomeration characteristics as the temperature is increased during the measurements. The ferrogel did not show any sedimentation or particle detachment from the gel under thermal cycling. Details of our results and analysis are presented.

We compare the characteristics of ferrogels prepared with and without the presence of a uniform magnetic field using Fe3O4 and Fe2O3 nanoparticles immobilized in hydrogels of N-isopropylacrylamide. The spatial distribution and agglomeration of the nanoparticles within the ferrogels were investigated using ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM). Hydrated ferrogels were also studied for magnetization using direct current superconducting quantum interference device (DC-SQUID). Volume size distribution resulting from USAXS data of the Fe3O4-ferrogel prepared under a uniform 225 G magnetic field showed a single broad peak appreciably different from that prepared without magnetic field with three distinct peaks. Volume size distributions resulting from USAXS data of the Fe2O3-ferrogel prepared with and without the presence of a uniform magnetic field both similarly show two peaks. Nanoparticle agglomeration was also determined by analyzing TEM images of ferrogel samples. DC-SQUID measurements of Fe3O4-ferrogel prepared in the presence of a uniform magnetic field showed 9% higher magnetization compared to the Fe3O4-ferrogel prepared without magnetic field. Similarly, DC-SQUID measurements of Fe2O3-ferrogel prepared in the presence of a uniform magnetic field showed 3% higher magnetization compared to the Fe2O3-ferrogel prepared without magnetic field. Thus, the presence of a uniform magnetic field during ferrogel polymerization can enabled the enhancement of the magnetoelastic property of the ferrogel.

This paper presents the results of our analysis of ferrogels prepared using uncoated and polyvinylpyrrolidone (PVP)-coated magnetite (Fe3O4) nanoparticles. The N-isopropylacrylamide (NIPAM) based hydrogel is used with 15-25 nm Fe3O4 nanoparticles different concentrations in the range 1.25 -14%. These samples were analyzed using ultra small angle x-ray scattering (USAXS), Transmission Electron Microscopy (TEM), and Direct-Current Superconducting Quantum Interference Devices (DC-SQUID) magnetometry. Samples prepared with polyvinylpyrrolidone (PVP) coated nanoparticles showed a better single particle distribution compared to uncoated samples. USAXS data indicated that the gels prepared using uncoated nanoparticles have a large two particle agglomerations. In both cases, the volume fraction of the particles in the gel is linearly proportional to the initial particle concentrations. The DC-SQUID magnetometry analysis indicated that the magnetic moment of the gel samples prepared with uncoated particles is ∼ 2emu/g compared to ∼1.5emu/g of those having coated particles.