De La Cruz-Montoya, Edwin

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    Synthesis and characterization of bulk and colloidal magnetic polymer nanocomposites
    (2013) De La Cruz-Montoya, Edwin; Rinaldi, Carlos; College of Arts and Sciences - Sciences; Hernández Rivera, Samuel P.; Aponte, María A.; Morell, Luis; Department of Chemistry; Jiménez, Esbal
    The development of bulk and colloidal latex polymer nanocomposites of poly (methyl methacrylate) (PMMA) with embedded magnetic nanoparticles particles was investigated. The first approach consisted of the preparation of magnetic PMMA nanocomposites using oleic acid coated cobalt ferrite and magnetite nanoparticles for subsequent characterization of their magnetic properties. It was found that the cobalt ferrite nanocomposite had magnetic hysteresis at 2 and 300 K as well as the magnetite nanocomposite had magnetic hysteresis at 2 K and superparamagnetic behavior at 300 K. Both nanofillers had a similar effect in shifting the glass transition temperature from that of the neat polymer. The influence of cobalt ferrite nanofiller surface chemistry on the thermal, mechanical, and magnetic properties of PMMA nanocomposites was also studied by comparing nanofillers coated with oleic acid (OA, which does not covalently bond to the PMMA matrix) and 3-methacryloxypropyltrimethoxysilane (MPS, which covalently bonds to the PMMA matrix). The values of the degradation temperature (Td) and glass transition temperature (Tg) increased relative to the neat amount polymery when the nanofillers were introduced into the nanocomposites. The greater increase in thermal stability of the nanocomposite with MPS-coated nanoparticles was due to chemical bonding between the acrylate group in MPS and the PMMA. The nanocomposite filled with nanoparticles functionalized with OA showed slightly higher values of magnetic saturation and coercivity compared with those grafted with MPS. Magnetic polymer nanospheres of PMMA with embedded CoFe2O4 nanoparticles were synthesized by magnetic miniemulsion polymerization. The average diameter of the CoFe2O4/PMMA nanospheres was controlled by varying the amount of surfactant. Dynamic light scattering analysis (DLS) of the magnetic polymer nanospheres showed that the average hydrodynamic diameter increased from 145 nm to 225 nm due to the increase in the concentration of the surfactant. The magnetic properties of nanospheres were investigated by measuring the magnetization curves and the complex susceptibility. The particles were found to respond to alternating fields by Brownian magnetic relaxation.