Rayleigh–Brillouin spectra of polymer fluids: Polyphenylmethyl siloxane and polydimethylphenylmethyl siloxane

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Abstract
Measurements of Rayleigh–Brillouin spectra of polyphenylmethyl siloxane (A) and of polydimethylphenylmethyl siloxane (B) over a wide range of temperatures (270 to 520 K for A; 280 to 390 K for B) are reported. By using the generalized hydrodynamic theory for Rayleigh–Brillouin spectra as developed by Lin and Wang, we have determined the relaxation strength R, the relaxation rate t, the activation energy Ea, and the adiabatic sound frequency ws (T), which are the characteristic physical quantities describing the dynamics of a viscoelastic polymer fluid in the GHz region. Based on those parameters, we were able to obtain excellent agreement between the theoretical and the measured spectra.

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