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.
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.
Kundu S.,Academy of Scientific and Innovative Research |
Kundu S.,CSIR - Central Electrochemical Research Institute |
Kundu S.,Rice University |
Yadav R.M.,Rice University |
And 10 more authors.
Nanoscale | Year: 2015
Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ∼2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants. © The Royal Society of Chemistry 2015.
Singh A.K.,Cl Jain College |
Kumar R.,Cl Jain College |
Singh U.,Cl Jain College |
Singh N.P.,Cl Jain College |
And 2 more authors.
International Journal of Heat and Mass Transfer | Year: 2011
In the present paper transient as well as non-Darcian effects on laminar natural convection flow in a vertical channel embedded in a porous medium in the presence of uniform magnetic field applied normal to the flow region is studied. Forchheimer-Brinkman extended Darcy model is assumed to simulate momentum transfer within the porous medium. Approximate solutions are obtained using multi-parameter perturbation technique. Variations in the velocity field with Darcy number, Grashof number, kinematic viscosity ratio and variations in the temperature distribution are obtained and depicted graphically. Expression for the skin-friction and the rate of heat transfer at the channel walls are also derived and the numerical values for various physical parameters are presented in tabular form. © 2011 Elsevier Ltd. All rights reserved.
Singh A.K.,Vssd College |
Agnihotri P.,Vssd College |
Singh N.P.,Rama Institute of Engineering and Technology |
Singh A.K.,Cl Jain College
International Journal of Heat and Mass Transfer | Year: 2011
The present study addresses the transient as well as non-Darcian effects on laminar natural convection flow in a vertical channel partially filled with porous medium. Forchheimer-Brinkman extended Darcy model is assumed to simulate momentum transfer within the porous medium. Two regions are coupled by equating the velocity and shear stress in the case of momentum equation while matching of the temperature and heat flux is taken for thermal energy equation. Approximate solutions are obtained using perturbation technique. Variations in velocity field with Darcy number, Grashof number, kinematic viscosity ratio, distance of interface and variations in temperature distribution with thermal conductivity ratio, distance of interface are obtained and depicted graphically. The skin-friction and rate of heat transfer at the channel walls are also derived and the numerical values for various physical parameters are tabulated. © 2010 Elsevier Ltd. All rights reserved.
Shukla R.K.,VSSD College |
Kumar A.,VSSD College |
Awasthi N.,VSSD College |
Srivastava U.,VSSD College |
Gangwar V.S.,VSSD College
Experimental Thermal and Fluid Science | Year: 2012
Densities, viscosities and refractive indices were measured for the binary liquid mixtures formed by formamide, N-methylacetamide, di-methylformamide and di-methylacetamide with acetonitrile at (T=293.15, 298.15, 303.15, 308.15 and 313.15). K and atmospheric pressure over the whole concentration range. Lorentz-Lorentz (L-L) relation, Prigogine-Flory-Patterson model (PFP), model devised by Glinski and Ramaswamy and Anbananthan (RS) models were used to study the associational behavior of weakly interacting liquids from viscosity and refractive index data. These non-associated and associated models were compared and also tested for different systems. The measured properties were fitted to Redlich-Kister polynomial relation to estimate the binary coefficients and standard errors. Furthermore, McAllister multi body interaction model was used to correlate the binary properties. Conclusively, viscosities and refractive indices of binary liquid mixture can be better understood from these models and interactions and association constant can be well predicted. The associated processes yield fair agreement between theory and experiment as compared to non-associated processes. © 2011 Elsevier Inc.
Yadav R.M.,VSSD College |
Dobal P.S.,VSSD College
Journal of Nanoparticle Research | Year: 2012
We have prepared bamboo-shaped C-N nanotubes-polyethylene oxide (PEO) composite films by solution cast technique and investigated their structural/microstructural and electrical properties and developed a correlation between them. The formation of clean compartmentalized bambooshaped C-N nanotubes was confirmed by TEM. SEM investigations revealed a homogeneous dispersion of nanotubes in PEO matrix. Enhanced electrical conductivity was observed for the C-N nanotubes- PEO composites than bare PEO. The conductivity measurements on the C-N nanotubes-PEO composite films with ̃20 wt % concentration of C-N nanotubes showed an increase of eight orders (̃7.5 9 10 -8 to 6.2 S cm -1) of magnitude in conductivity from bare PEO film. Raman spectra showed the stressfree nature of the composites and established the bonding of nanotubes with PEO, which resulted in the variation of Raman parameters. The Raman data of composites corroborate the findings of variation in electrical conductivity. © Springer Science+Business Media B.V. 2012.
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.