Rayleigh-Brillouin Scattering and Structural Relaxation of a Viscoelastic Liquid.
UTAH UNIV SALT LAKE CITY DEPT OF CHEMISTRY
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The linear response theory using a complete set of dynamic variables involving density, velocity and energy fluctuations is used to analyze the Rayleigh-Brillouin spectrum of a viscoelastic liquid. An exact equation including the effect of structural relaxation has been obtained. The result is disscussed in the fast and slow relaxation limits. In the former case, the Rayleigh-Brillouin spectrum is identical to that predicted by the classical hydrodynamic equations, whereas in the latter case a new structural central peak is found, in addition to the anomalous dispersion and relaxation effects present in the frequency and linewidth data associated with the Brillouin peak. The evolution of structural relaxation and its effect on the entire Rayleigh-Brillouin spectrum is described. The structural central peak is most pronounced with the frequency dispersion and the linewidth maximum are present. The theoretical result has been used to calculate the Rayleigh-Brillouin spectra of polypropylene glycol at various temperatures. The results of the frequency shift, the spectral linewidth and the Landau-Placzek ratio are in good agreement with the experiment. Author
- Fluid Mechanics