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Beaumont, TX, United States

Zhang X.,Integrated Composites Laboratory ICL | Wei S.,Lamar University | Haldolaarachchige N.,Louisiana State University | Colorado H.A.,University of California at Los Angeles | And 3 more authors.
Journal of Physical Chemistry C

Polyaniline (PANI) polymer nanocomposites (PNCs) filled with barium titanate (BaTiO 3) were synthesized by a surface initiated polymerization method. Two different particle sizes (100 and 500 nm) were studied. By varying the loading level, size of BaTiO 3 nanoparticles (NPs) and stirring method for the polymerization process, a series of PNCs were obtained and the effects of these parameters on the crystalline structure, thermal stability, morphology, electrical conductivity and dielectric permittivity were systematically studied. FT-IR analysis indicated a strong interaction between the formed PANI and the BaTiO 3 NPs, and TEM observations showed that the BaTiO 3 NPs are well coated with a PANI layer, however, the thickness of the PANI layer decreased with increasing the BaTiO 3 particles loading. The XRD reflection patterns indicated that the crystallinity of the polyaniline part in the PNCs depends on the nanoparticle loading. However, the resistivity does not increase with increasing the crystallinity, and the temperature dependent resistivity result reveals a 3-d variable range hopping (VRH) electron transport mechanism. The BaTiO 3 loading dependent resistivity is interpreted from the dominating space charge on the BaTiO 3/PANI interface and the ferroelectric nature of BaTiO 3 for the PNCs with different particle loadings. Compared with the positive real permittivity for the PNCs prepared from physical mixing, all the chemically synthesized PNC samples show negative dielectric permittivity and the permittivity change is related to the instinct metallic state in PANI. In addition, positive magnetoresistance (MR) is observed in all kinds of PNCs and analyzed theoretically from the wave function shrinkage model. © 2012 American Chemical Society. Source

He Q.,Integrated Composites Laboratory ICL | He Q.,Lamar University | He Q.,Engineered Multifunctional Composites LLC | Yuan T.,Integrated Composites Laboratory ICL | And 14 more authors.
Journal of Physical Chemistry C

Highly efficient electromagnetic field absorption at gigahertz (GHz) was reported in the novel magnetic polymer nanocomposites (MPNCs) with in-situ synthesized Fe@Fe2O3 core@shell nanoparticles (NPs) or their decorated multiwall carbon nanotubes (MWNTs) dispersed in the polypropylene (PP) matrix through a one-pot bottom-up method. PP grafted maleic anhydride (PP-g-MA) with different molecular weights served as surfactant to stabilize the in-situ-formed NPs and simultaneously as compatibilizer to enhance the bonding at the PP-filler interfaces. Because of the strong magnetization of the PP MPNCs filled with 20.0 wt % Fe@Fe2O3 NPs stabilized by PP-g-MA (Mn = 800), a minimum reflection loss (RL) of -31.5 dB was observed at 18.0 GHz, and the frequency bandwidth with RL lower than -10.0 dB was 3.1 GHz (from 16.9 to 20.0 GHz) in the MPNC sample with a thickness of 5.5 mm. However, due to the lack of magnetic loss, only a weak RL of 4.3 dB was found at frequency of 16.8 GHz for the PP/PP-g-MA (Mn = 800)/1.0 wt % MWNTs nanocomposites sample with a thickness of 5.5 mm. When the PP MPNCs filled with Fe@Fe2O3 NPs decorated MWNTs (sample thickness of 5.0 mm) in the presence of low molecular weight PP-g-MA (Mn = 800), the RL of -24.5 dB at 20.0 GHz was observed. Through simply changing Mn of PP-g-MA from 800 to 8000, more oxidized iron resulted in a decreased permeability and smaller RL in the high frequency range. The in-situ-formed nanofillers significantly reduced the flammability of PP for potential wide applications. © 2014 American Chemical Society. Source

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