Rayleigh–Brillouin scattering studies of segmental fluctuations in poly(siloxanes)

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Abstract
New results from a detailed temperature dependent Rayleigh–Brillouin study of siloxane polymers are reported. The study includes the examination of the effect of the relaxation of the longitudinal stress modulus on the propagation behavior of the thermally driven acoustic wave in the 109 Hz frequency range. The Rayleigh–Brillouin spectra of poly(diphenyl siloxane), poly(phenylmethyl siloxane) as well as their model analogs, 1,3‐tetraphenyl 1,3‐dimethyl disiloxane, and 1,3‐diphenyl 1,2‐tetramethyl disiloxane are measured over a wide range of temperature covering from Tg to 240 K above Tg. The theory for Rayleigh–Brillouin scattering has also been reformulated in such a way that the parameters which enter the theory are in terms of easily recognizable thermodynamic and transport coefficients.