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Kānpur, India

Pandey M.B.,Vssd College | Verma R.,Allahabad University | Dhar R.,Allahabad University
Israel Journal of Chemistry | Year: 2012

Antiferroelectric liquid crystals (AFLCs) are a recent class of materials in the family of liquid crystals which have high prospect of application in displays with better results as compared to conventional nematic displays. Beside technological applications, AFLCs are very interesting from the point of view of basic studies in soft condensed matter systems as these materials are showing various new sub-phases, viz. SmC α *, SmC β *, SmC a * and many others with distinct macroscopic properties in a narrow temperature region in addition to the most common wide-range low-temperature SmC a * phase. In the present article, we report the structure of various sub-phases of AFLCs, their dielectric behaviour and the electro-optical response of some of the materials studied by our group. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kumar R.,University of Campinas | Singh R.K.,Banaras Hindu University | Dubey P.K.,Allahabad University | Singh D.P.,University of Santiago de Chile | And 2 more authors.
Advanced Materials Interfaces | Year: 2015

3D hierarchical structures are reported based on graphene-nickel encapsulated nitrogen-rich aligned bamboo like carbon nanotubes, which show not only high-performance supercapacitance behavior but also a great robust cyclic stability. A facile synthesis route is developed of 2D nickel oxide decorated functionalized graphene nanosheets (2D-NiO-f:GNSs) hybrids and 3D nitrogen doped bamboo-shaped carbon nanotubes (NCNTs) vertically standing on the functionalized graphene nanosheets (3D-NCNT@f:GNSs) by using a thermal decomposition method. The chemical reduction and morphology-dependent electrochemical response are investigated. The enhanced specific capacitance of 3D-NCNT@f:GNSs as compared to that of 2D-NiO-f:GNSs suggests the synergistic effects and indicates the importance of energy storage and superior long-term cycling performance that are achieved. This 3D-NCNT@f:GNSs hybrid shows a remarkable cycling stability with a maximum power density of 12.32 kW kg-1 and maximum energy density of 109.13 Wh kg-1 due to the good connection of NCNT and f:GNSs. This unique 3D nano network architecture enables the availability of large surface areas of NCNT, thus endowing the nanohybrids with high specific capacitance and excellent reusability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Garg M.S.,H+ Technology | Srivastava K.,Vssd College | Srivastava D.,H+ Technology
Progress in Organic Coatings | Year: 2015

Cardanol-based vinyl ester resin (CVER) was blended with varying concentrations of Carboxyl terminated butadiene acrylonitrile (CTBN) ranging between 0 and 15 wt% with an interval increment of 5 wt%, by two different approaches, viz., physical and chemical blending. The formation of various products during the curing of blend samples has been studied by FTIR spectroscopic analysis. The dynamic DSC scans showed that the blend samples of CVERs cured in the temperature range of 100-150 °C. It was observed that the blend sample containing 5 wt% and 10 wt% liquid rubber, for physical and chemical blending, respectively, showed least cure time, at 120 °C, amongst all other blend samples. On evaluation, it was found that in toughened samples thermal and mechanical properties were marginally affected with the increase of CTBN concentration. The blend morphology, studied by scanning electron microscopy analysis, showed the presence of precipitated discrete rubber particles which dispersed throughout the vinyl ester matrix, i.e., they revealed the presence of two phase morphology. © 2014 Elsevier B.V. All rights reserved.

Pandey M.B.,Vssd College | Dhar R.,Allahabad University | Dabrowski R.,Military University of Technology
Molecular Crystals and Liquid Crystals | Year: 2011

Chiral compounds show rich variety of smectic phases viz. SmCα*, SmCβ*, SmCγ*, SmC*, SmCA* due to different correlation between adjacent layers and various TGB phases due to different orientation of blocks of layers. Dielectric spectroscopy has proven as an important tool for the characterization of various smectic phases posses by chiral compounds. Dielectric spectra of these phases are sometimes complex but rich in information and are very helpful in the determination of the structure of these phases. Dielectric spectroscopy of the above phases observed in the recently synthesized materials is discussed with regards to their structure property relationship. Copyright © Taylor & Francis Group, LLC.

Pandey M.B.,University of Colorado at Boulder | Pandey M.B.,Vssd College | Porenta T.,University of Ljubljana | Brewer J.,University of Colorado at Boulder | And 7 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We describe dipolar nematic colloids comprising mutually bound solid microspheres, three-dimensional skyrmions, and point defects in a molecular alignment field of chiral nematic liquid crystals. Nonlinear optical imaging and numerical modeling based on minimization of Landau-de Gennes free energy reveal that the particle-induced skyrmions resemble torons and hopfions, while matching surface boundary conditions at the interfaces of liquid crystal and colloidal spheres. Laser tweezers and videomicroscopy reveal that the skyrmion-colloidal hybrids exhibit purely repulsive elastic pair interactions in the case of parallel dipoles and an unexpected reversal of interaction forces from repulsive to attractive as the center-to-center distance decreases for antiparallel dipoles. The ensuing elastic self-assembly gives rise to colloidal chains of antiparallel dipoles with particles entangled by skyrmions. © 2014 American Physical Society.

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