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Manufacturing and characterisation of PMMA-graphene oxide (GO) nanocomposite sandwich films with electrospun nano-fibre core

Upadhyay J, Das R., Rao S., Liu D., Bhattacharyya D

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

835--840

EN

Purpose: Nanocomposite materials, comprising of polymer matrices and nano-sized reinforcements, exhibit significantly enhanced mechanical and functional properties at extremely low filler loading. In recent years, graphene oxide (GO) has emerged as a new class of low cost nano-filler with high mechanical strength and stiffness, and alterable electrical properties. For nano-fillers with layered structure like GO, complete exfoliation and uniform dispersion of filler in the polymer matrices is essential to enhance the matrix-filler interaction and in turn the mechanical and/or functional property improvement. Conventional nanocomposite manufacturing methods including in-situ polymerisation and solvent processing encounter the problem of agglomeration of GO films. Additionally, its low bulk density presents difficulties in handling, and the energy requirement for mechanical mixing and extrusion processes is very high. In this work, we report manufacturing of poly(methyl methacrylate)-graphene oxide (PMMA-GO) nano-fibre mat using relatively novel approach of employing electrospinning technique. The manufactured electrospun core was inserted between plain polymer layers to prepare a robust and easy to handle sandwich film. Morphology and structure of the PMMA-GO nano-fibre cores was evaluated with scanning and transmission electron microscopy and X-ray diffractometry. The manufactured nano-fibre mat samples exhibited uniform diameter and dispersion. The functional parameters including thermal stability and gas barrier were evaluated with differential scanning calorimetry and oxygen permeation testing, and these functional properties were observed to be superior to that of monolithic polymer counterparts.

2

Turbulence in mobile-bed streams

Dey S., Das R., Gaudio R., Bose S.

Acta Geophysica

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2012

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Vol. 60, no. 6

1547-1588

EN

This study is devoted to quantify the near-bed turbulence parameters in mobile-bed flows with bed-load transport. A reduction in near-bed velocity fluctuations due to the decrease of flow velocity relative to particle velocity of the transporting particles results in an excessive near-bed damping in Reynolds shear stress (RSS) distributions. The bed particles are associated with the momentum provided from the flow to maintain their motion overcoming the bed resistance. It leads to a reduction in RSS magnitude over the entire flow depth. In the logarithmic law, the von Karman coefficient decreases in presence of bed-load transport. The turbulent kinetic energy budget reveals that for the bed-load transport, the pressure energy diffusion rate near the bed changes sharply to a negative magnitude, implying a gain in turbulence production. According to the quadrant analysis, sweep events in mobile-bed flows are the principal mechanism of bed-load transport. The universal probability density functions for turbulence parameters given by Bose and Dey have been successfully applied in mobile-bed flows.

3

Kinetics and Mechanism of Complex Formation between O-Bonded Pentaammine(valinato/prolinato)cobalt(III) Ions and Nickel(II) in Aqueous Medium

Dash A., Brahma G., Mohanty P., Das R.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 7

987-995

EN

The kinetics of reversible complexation of Ni(OH2)6 2+ with oxygen-bonded valinato/prolinatocobalt( III) substrates, (NH3)5Co(val/pro)3+ have been investigated by stopped flow technique at 25_C, 6.1_ pH_6.70 and I = 0.3 mol dm-3. The formation of binuclear species, [(NH3)5Co(val/pro)Ni]4+, occured via the reaction of Ni(OH2)6 2+ with deprotonated (amine and imine functions of valine and proline, respectively) form of the cobalt(III) substrates, (NH3)5Co(val/pro)2+. The results indicate the formation of mono-bonded binuclear species through entry of the imine/amine functions into the coordination sphere of Ni(II) with Ni-OH2 bond dissociation is limiting (Id mechanism). The binuclear species exist in dynamic equilibrium involving the mono-dentate and chelated forms with chelated forms predominating. The small values of dissociation rate constants, despite the intrinsic electrostatic repulsion between the like charge centers, also support the chelate nature of the binuclear species.