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Archita Patnaik
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Archita Patnaik
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Archita Patnaik
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Patnaik, A.
Patnaik, Archita
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10 results
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- PublicationCrystal structure of an ammonium thiocyanate complex of 18crown-6(01-05-2004)
;Bokare, Alok D.The title compound (C13H30N2O 7S) has been determined from three-dimensional X-ray diffraction data. The crystals are monoclinic, a = 22.654(8) Å, b = 8.652(4) Å, c = 23.925(9) Å, β= 123.880(9)°, V= 3893(3) Å3, Z = 8, Dcalc =1.192 g/cm3, space group C2/c. The structure was solved by direct methods and refined by full-matrix least squares method (R = 0.051). The ammonium cation is displaced by 1.08 Å from the mean plane of the ligand causing hydrogen bonding with the macrocyclic O atoms in a perching arrangement. The thiocyanate anion forms an extended hydrogen bonded chain with the cation via the occluded water molecule. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. - PublicationEvidence for C60 aggregation from solvent effects in [Ps-C 60] molecular complex formation(14-10-2003)
;Bokare, Alok D.Using a molecular probe positronium (Ps), Ps reaction rate constants (k) with C60, a strong Ps acceptor, are determined for the formation of a donor-acceptor type molecular complex in solvents of varying surface tension (σ) and viscosity (η). Within the framework of Smoluchowski's theory of diffusion, the calculated Stokes radius for C60 in the different solvents deviated from the monomeric value, implying the existence of aggregated clusters in solution and using transmission electron microscopy, C60 aggregation in carbon disulphide (CS2) is observed with the formation of spherical fractal clusters of ̃90 nm size with aggregation number 1.7 × 104 and a fractal dimension of 1.9 at a concentration of 0.5 mM. The fractal dimension of 1.9 revealed the mechanism of aggregation to proceed through a diffusion limited process with the estimated diffusion coefficient and the diffusion length of the aggregated cluster to be 2.27 × 10-6 cm2/s and 0.63 nm, respectively. © 2003 Elsevier Ltd. All rights reserved. - PublicationC60 aggregate structure and geometry in nonpolar o-xylene(13-01-2005)
;Bokare, Alok D.Consequent to our recent papers on C60 colloidal aggregates in CS2 solution (Bokare, A. D.; Patnaik, A. J. Phys. Chem. 2003, 107, 6079-6086) and their probable electron density distribution (Bokare, A. D.; Patnaik, A. J. Chem. Phys. 2003, 119, 4529-4538), the solution-phase structure of C60 in nonpolar o-xylene is reported using a positronium (Ps) atom as a fundamental probe, mapping changes in the local electron density of the microenvironment. Spontaneous formation of stable aggregates in the colloidal range (∼90-150 nm) was observed in a concentration range of 0.14-0.36 g/dm3, beyond which they broke. An onset concentration for aggregate formation at 0.14 g/dm3, as against 0.06 g/dm3 for the polar CS2 solvent, was noted and was substantiated by complete quenching of pyrene fluorescence at and beyond this onset due to photoinduced electron transfer from the pyrene excited state to the C60 aggregate. An order-disorder phase transition led to a notable geometry change of the colloidal particles; a sphere-to-nonuniform cylinder transition following an increase in the C60 concentration from 0.14 to 0.36 g/dm3 revealed the aggregate curvature/internal modes to have been influenced by energetic/entropic and/or hydrodynamic interactions in the solvent medium. Transmission electron microscopy images of the aggregated clusters, in corroboration with Ps annihilation characteristics and pyrene fluorescence, revealed the clusters to be hexagonally close packed microcrystals. - PublicationExistence of a third crystalline phase in TBBA(01-01-2003)
;Bokare, Alok D.Positron annihilation lineshape (S-parameter) measurements and small angle X-ray scattering (SAXS) using synchrotron X-rays on liquid crystalline terepthal-bis-butylaniline (TBBA) are reported at cryogenic temperatures. The crystalline ↔ crystalline transition at 233 K deviates from the first order nature, as evidenced by the observation of a pronounced hysteresis in the layer spacing and the S-Parameter during the heating and cooling cycles. Presence of a possible third crystalline phase at a still lower temperature of 180K is identified from X-ray diffraction patterns in corroboration with the slope change in layer spacing and electron density variations reflecting on the line-shape parameter. - PublicationSelf-organization of C60 nanoparticles in carbon disulfide solution(26-07-2003)
;Bokare, Alok D.C60 aggregation in neat CS2 solvent is reported using positronium (Ps) as a fundamental probe, which maps changes in the local electron density of the microenvironment. Specific interactions of the Ps atom with the surrounding dramatically reveal the onset concentration for stable aggregate formation in this solvent to be 0.06 g/dm3. Spontaneous formation of stable aggregates in the colloidal range (∼90-125 nm) was observed over a narrow concentration range of 0.06-0.36 g/dm3, beyond which the clusters broke. Variation of aggregate properties with size (proportional to τ3 [Ps lifetime] and/or λ3 [Ps annihilation rate, 1/τ3]) are noteworthy. Ps annihilation characteristics in corroboration with transmission electron microscopy and UV-vis absorption spectroscopy demonstrate the solution phase C60 structure to be a spherical fractal aggregate with fractal dimension 1.9 and that the growth mode follows a diffusion-limited cluster aggregation mechanism. At a higher concentration beyond 0.36 g/dm3, an entropy driven phase change was noticed leading to formation of irregular, but oriented crystalline components. - PublicationMicroscopic diffusion model applied to C60 fullerene fractals in carbon disulphide solution(22-08-2003)
;Bokare, Alok D.A microscopic diffusion model calculating the o-Ps lifetimes in C60 aggregated solutions in CS2 solvent was adopted. An excellent agreement between the calculated and experimental o-Ps lifetimes in the aggregated solutions reflected on important quantitative parameters of the system. These observations followed the concentration dependent structure attribution to the C60 aggregates obtained from a microscopic picture of the Ps surroundings in the C60 solution and from TEM. Existence of several competing mechanisms during solubilization were observed and an increasing interaction between the C60 molecules resulted in a displacement of equilibrium towards the solid state. - PublicationStructure of mesogenic 4′-hexadecyloxy-3′-nitrobiphenyl-4- carboxylic acid (ANBC-16) at the air-water interface(01-01-2002)
;Bokare, Alok D.The Langmuir film behavior of an amphiphilic thermotropic mesogen at the air-water interface has been studied from surface pressure-molecular area isotherms. The isotherms exhibited a transition from an expanded to a condensed phase and on further compression also indicated the formation of an unstable monolayer, evidenced through a pronounced hysterisis observed during the decompression cycle. This phenomenon is explained on the basis of stronger hydrophobic forces dominating the orientation in the condensed phase. Increase in the limiting molecular area at lower temperatures provides supporting evidence for the observed loss of a stable condensed phase, which is attributed to the dissolution of the molecules into the aqueous subphase. - PublicationRotational flexibility in NH4+-encapsulated 18-crown-6 studied by molecular dynamics and positron annihilation: Where does the positron localize?(24-02-2005)
;Bokare, Alok D.Conformational flexibility of the ammonium complex of macrocyclic 18-crown-6 at 100 K ≤ T ≤ 300 K is studied using a positron microprobe in conjunction with molecular dynamics simulations. The ammonium cation, encapsulated in a three-pointed hydrogen-bonding perching arrangement, undergoes unhindered facile rotation inside the crown cavity, and the ether backbone adopts itself to the dynamic cation conformation. Preferential localization of the positron in the vicinity of the encapsulated cation results in the positron sensing changes in the local electron density distribution arising from the unrestricted rotational motion of the cation as well as from the slow motion of the crown backbone and hence sensing only an average conformation of the complex. © 2005 American Chemical Society. - PublicationOrientational ordering in polymorphic terepthal-bis-4-butylaniline (TBBA)(01-05-2002)
;Bokare, Alok D. ;Das, Dipankar ;Amenitsch, HeinzIndividual molecular tilt angle behavior in the smectic C region is represented upon application of a molecular statistical model to the polymorphic terepthal-bis-butylaniline (TBBA) in conjunction with the experimental layer spacings from SAXS measurements using the synchrotron X-ray beam. In the smectic A and smectic H phases of the mesogen, the order parameter fluctuations and pre-transitional effects responsible for sharp changes in the layer spacing and scattered intensities near the phase transition temperature are corroborated with varying positron annihilation lineshapes as a result of electron density fluctuations. © 2002 Published by Elsevier Science Ltd. - PublicationRecoil tritium-C60 interaction: A channel for endohedral encapsulation of tritium in C60(23-09-2002)
;Sahoo, Rashmi R. ;Bokare, Alok D.The introduction of tritium (T), with an initial kinetic energy of 2.7 MeV into the cavity of C60 using recoil implantation is studied in a 6Li(n,α)T activated homogenized compound matrix of Li2CO3 and C60. Radioactive endohedral T@C60 could be detected through the liquid scintillation spectrometry coupled with high-pressure liquid chromatography (HPLC). Fast atom bombardment mass spectrometry provided evidence for the retainment of C60 cage as against radiation damage. Solid state temperature-programmed desorption based on evolved gas showed the desorption of 3He gas (as a β- decay product from T) from the endohedral C60 cage at a higher temperature than the T2 and T2O trapped species at the defect sites and from the ordered crystallographic network of Li2CO3, respectively. The non-isothermal kinetics of the helium desorption, as a function of temperature evidenced a diffusion controlled process. © 2002 Elsevier Science Ltd. All rights reserved.