Light scattering from nonequilibrium concentration fluctuations in a polymer solution
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2000
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American Institute of Physics
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Abstract
We have performed light-scattering measurements in dilute and semidilute polymer solutions of polystyrene in toluene when subjected to stationary temperature gradients. Five solutions with concentrations below and one solution with a concentration above the overlap concentration were investigated. The experiments confirm the presence of long-range nonequilibrium concentration fluctuations which are proportional to (del T)(2)/k(4), where del T is the applied temperature gradient and k is the wave number of the fluctuations. In addition, we demonstrate that the strength of the nonequilibrium concentration fluctuations, observed in the dilute and semidilute solution regime, agrees with theoretical values calculated from fluctuating hydrodynamics. Further theoretical and experimental work will be needed to understand nonequilibrium fluctuations in polymer solutions at higher concentrations.
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© 2000 American Institute of Physics. We are indebted to J. F. Douglas for valuable discussions and to S. C. Greer for helpful advice concerning the characterization of the polymer sample. J.V.S. acknowledges the hospitality of the Institute for Theoretical Physics of the Utrecht University, where part of the manuscript was prepared. The research at the University of Maryland is supported by the U.S. National Science Foundation under Grant CHE 9805260. J.M.O.Z. was funded by the Spanish Department of Education during his postdoctoral stage at Maryland, when part of the work was done.