Light scattering study of Salol: Exploring the effect of rotation -translation coupling.
Item
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Title
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Light scattering study of Salol: Exploring the effect of rotation -translation coupling.
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Identifier
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AAI3144157
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identifier
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3144157
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Creator
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Zhang, Hepeng.
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Contributor
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Adviser: Herman Z. Cummins
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Date
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2004
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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Extensive light scattering experiments, including Brillouin, Raman and photon correlation spectroscopies, have been done to study the rotational and translational dynamics and their coupling in a glassforming liquid of anisotropic molecules, Salol. Pick-Franosch theory was used to fit the full set of data.;VH backscattering spectra were first fit with a hybrid function. This part of the analysis, together with photon correlation data, fixed all the parameters characterizing the pure rotational dynamics. The obtained rotational relaxation times agree with the results of dielectric and other experiments in the literature.;In VH 90° fitting, the Pick-Franosch theory can produce excellent fits to all 23 spectra from 380 K to 210 K. At temperatures from 380 K to 310 K, the static shear viscosity values obtained from the fits agree with published theological results. From 280 K to 210 K, the relaxation time for shear viscosity was found to be proportional to, and 15 times smaller than, the rotational relaxation time. The stretching coefficient beta for shear viscosity is smaller than that for rotational relaxation and the strength of rotation-translation coupling increases with decreasing temperature.;The difference spectra between VV 90° and VH backscattering spectra were analyzed last with the help of parameters obtained from both VH backscattering and VH90° fittings. The difference spectrum shows negative region-VV dip-at high temperatures and low frequencies. The difference spectra were first analyzed by a density-fluctuation-only model, which neglects the rotation-translation coupling. It can fit difference spectra well except where VV dip is. However, the Pick-Franosch theory, which includes rotation-translation coupling, can fit all the difference spectra including the VV dips. Thus we conclude that the VV dip is a consequence of rotation-translation coupling and related to---but less apparent than---the Rytov dip in the VH 90° spectra. The bulk viscosity was found to be roughly equal to the shear viscosity from 250 K to 350 K. Compared with the shear viscosity obtained from density-fluctuation-only fits, we found that rotation-translation coupling reduces the shear viscosity by roughly 15%.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
