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Title: Dielectric relaxation phenomena of some aprotic polar liquids under giga hertz electric field
Authors: Karmakar, A
Mitra, U K
Dutta, K
Sit, S K
Acharyya, S
Keywords: Dielectric relaxation
Aprotic polar liquids
Dipole moment
Issue Date: Nov-2006
Publisher: CSIR
IPC CodeG01R27/26
Abstract: The two relaxation times 1 and 2 due to rotations of the flexible parts and the whole molecules of some aprotic polar liquids (j) like N, N-dimethyl sulphoxide (DMSO); N, N-dimethyl formamide (DMF), N, N-dimethyl acetamide (DMA) and N, N-diethyl formamide (DEF) in benzene (i) are estimated from the measured real ij' and imaginary ij'' part of hf complex dielectric orientational susceptibility ij* and low frequency susceptibility oij at different weight fractions wj’s of solute at various experimental temperatures [Saha et al., J Phys. D: Appl Phys, 27 (1994) 596]. The relative contributions c1 and c 2 due to 1 and 2 are calculated from Fröhlich’s equations and graphical technique. All the c’s are positive from Fröhlich’s equations while some c2’s are negative from graphical method. The dipole moments 2 and 1 in Coulomb-metre (C.m) measured from the slope β’s of ij'–wj curves are compared with those of conductivity σij measurements using ’s from the ratio of individual slope of (dij''/dwj)wj→o and (dij'/dwj)wj→o, linear slope of ij''–ij' along with Gopalakrishna’s method [Trans Faraday Soc, 53 (1957) 767]. The estimated 1’s agree with the measured and reported ’s to indicate that the flexible part of the molecule is rotating under GHz electric field. The theoretical dipole moment theo’s are obtained in terms of available bond moments of the substituent polar groups attached to the parent molecules acting as pusher or puller of electrons due to inductive, mesomeric and electromeric effects in them under hf electric field. The variation of 1 with temperature suggests the elongation of bond moments. The energy parameters such as enthalpy of activation ΔH , free energy of activation ΔF and entropy of activation ΔS ’s are obtained for DMSO only assuming dielectric relaxation as a rate process to know the molecular dynamics. The variation of ln( 1T) against 1/T of DMSO reveals that it obeys Eyring rate theory unlike ln( 2T) against 1/T curve.
Page(s): 856-866
ISSN: 0975-1041 (Online); 0019-5596 (Print)
Source:IJPAP Vol.44(11) [November 2006]

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