Browsing by Author "Joshi, Mangala"

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Electrical and Dielectric Properties of Exfoliated Thermally Reduced Graphene Based Polyurethane Nanocomposites
(2017-12-01)
Bansala, Taruna
;
Joshi, Mangala
;
Mukhopadhyay, Samrat
;
Doong, Ruey-An
;
Chaudhary, Manchal
Thermally reduced graphene nanosheets (TRG) were prepared by using thermal exfoliation followed by annealing and then were served as fillers to well disperse in thermoplastic polyurethane (TPU) in a concentration range of 0.5-5.5 vol.%. The electrical conductivity, dielectric and mechanical properties of as-prepared TPU/TRG nanocomposite thin films were examined. The DC electrical conductivity was improved up to 3 x 1x10(-2) S m(-1) for the 5.5 vol.% TPU/TRG nanocomposite in comparison to 2 x 81x10(-11) S m(-1) for neat TPU matrix. Addition of TRG nanosheets enhanced the Young's modulus but reduced the strain-at-break and tensile strength of the nanocomposite films. The dielectric behavior including dielectric constant (epsilon) and tangent loss varied with the TRG loading in the nanocomposites. Results showed the increase in dielectric constant from 1 to 550 as well as the increase in tangent loss from 0.03 to 350 upon increasing concentration of TRG in the frequency range of 20-106 Hz. The high dielectric constant values in the low frequency region is mainly attributed to the Maxwell-Wagner polarization effect, while high values of tangent loss is contributed from the current leakage through the electrically conducting network of TRG sheets formed within the TPU matrix at high filler loadings.
Electrically conducting graphene-based polyurethane nanocomposites for microwave shielding applications in the Ku band
(2017-02)
Bansala, Taruna
;
Joshi, Mangala
;
Mukhopadhyay, Samrat
;
Doong, Ruey-an
;
Chaudhary, Manchal
Electrically conducting, thermally reduced graphene nanosheets (TRG) were synthesized through thermal exfoliation and subsequent annealing of graphene oxide at 800 A degrees C. Thermoplastic polyurethane (TPU)-based nanocomposites with different concentrations (ranging between 0 and 5.5 vol%) of TRG nanosheets were prepared by the solution blending method. Morphology, phase purity, and conducting properties of TPU and TPU/TRG nanocomposites were investigated through scanning electron microscopy, X-ray diffraction, conductive atomic force microscopy (C-AFM) and Raman spectroscopy. C-AFM images show the presence of electrically conducting TRG nanosheets embedded in the TPU matrix. Electromagnetic interference (EMI) shielding measurements were also undertaken on 2-mm-thick rectangular pellets. Shielding parameters such as shielding effectiveness, DC electrical conductivity, and dielectric properties, i.e., real and imaginary parts of permittivity were investigated. Our results show that the TPU/TRG nanocomposite at 5.5 vol% loading exhibits an enhanced electrical conductivity of the order of 3.1 x 10(-2) S/m and shows a superior EMI SE of similar to-26 to -32 dB in the Ku band frequency region. EMI shielding values were found to be dominated by the material\'s absorption behavior. The dielectric properties of TPU/TRG nanocomposites were also analyzed, and they demonstrate a good correlation with EMI shielding.
Synthesis and shielding properties of PVP-stabilized-AgNPs-based graphene nanohybrid in the Ku band
(2016-11)
Bansala, Taruna
;
Mukhopadhyay, Samrat
;
Joshi, Mangala
;
Doong, Ruey-an
;
Chaudhary, Manchal
PVP-stabilized silver nanoparticles (AgNP)-based graphene nanohybrid (Ag-PVP-CRG) have been synthesized and high performance shields for electromagnetic interference (EMI) in the microwave region have been developed. Morphological characterization of Ag-PVP-CRG nanohybrid by scanning electron microscopy, X-ray diffraction and high resolution transmission electron microscopy revealed PVP-stabilized AgNPs (diameter: 15-30 nm) decorated graphene sheets. The Ag-PVP-CRG nanohybrid showed excellent shielding response in the Ku band frequency region, which is majorly governed by absorption losses. The results show that the total EMI shielding effectiveness (SE) value is 58 dB for Ag-PVP-CRG at 2.0 mm thickness in the Ku-band region, dominated by absorption mechanism, which overpowered the 10 dB value of graphene oxide. The presence of AgNPs on graphene sheets enhances space charge polarization, multiple scattering and effective anisotropy energies of the nanohybrid, resulting in high electromagnetic shielding effectiveness. The dielectric behavior was evaluated to correlate with the EMI shielding mechanism. (C) 2016 Elsevier B.V. All rights reserved.