Browsing by Author "Narayanan, T.N."

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    Fluorinated graphene oxide for enhanced S and X-band microwave absorption
    (AIP Publishing LLC, 2015) Sudeep, P.M.; Vinayasree, S.; Mohanan, P.; Ajayan, P.M.; Narayanan, T.N.; Anantharaman, M.R.
    Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methyl Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations.
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    Large enhanced dielectric permittivity in polyaniline passivated core-shell nano magnetic iron oxide by plasma polymerization
    (AIP Publishing, 2014) Joy, Lija K.; Sooraj, V.; Sajeev, U.S.; Nair, Swapna S.; Narayanan, T.N.; Sethulakshmi, N.; Ajayan, P.M.; Anantharaman, M.R.
    Commercial samples of Magnetite with size ranging from 25-30nm were coated with polyaniline by using radio frequency plasma polymerization to achieve a core shell structure of magnetic nanoparticle (core)-Polyaniline (shell). High resolution transmission electron microscopy images confirm the core shell architecture of polyaniline coated iron oxide. The dielectric properties of the material were studied before and after plasma treatment. The polymer coated magnetite particles exhibited a large dielectric permittivity with respect to uncoated samples. The dielectric behavior was modeled using a Maxwell-Wagner capacitor model. A plausible mechanism for the enhancement of dielectric permittivity is proposed.