Localized segmental motion and Brillouin scattering in a polymer liquid

Abstract

Using polyethylene glycol as an example, it is shown that the relaxation of the longitudinal stress modulus manifest in Brillouin scattering is associated with localized conformational dynamics involving only transitions of few chain segments from one isometric state to another. Both the Debye and the Hall-Helfand models are adequate to the description of the dispersion and attenuation of the hypersonic wave in PEG. The Hall-Helfand model is more theoretically satisfactory than the Debye model, since it does not involve an artificially added term for the Brillouin linewidth.