Temperature Dependence of Dynamic Light Scattering in the Intermediate Momentum Transfer Region

Dynamic light scattering measurements have been made on dilute solutions of very high molecular weight polystyrenes in cyclohexane at 35.4, 45.0, and 55.2 °C. The data have been analyzed in terms of the first cumulant Ω(q) of the dynamic structure factor S(q,t), with particular emphasis on the intermediate momentum transfer region [formula-omitted], for which theoretical predictions yield Ω(q) ~ q3. The temperature dependence of the magnitude of Ω(q) is examined in terms of a “modified blob” model for the equilibrium distribution function and the preaveraged Oseen tensor description of hydrodynamic interaction. The temperature dependence of the experimental results is found to be in very good agreement with the theoretical calculations, although the magnitude of Ω(q) at each temperature falls consistently slightly below (-15%) the theoretical predictions, as reported previously for both good solvent and 6 conditions.