Temperature dependence of hydrodynamic dimensions of polystyrenes in cyclohexane by quasielastic light scattering

The quasielastic light scattering measurements of diffusion coefficients of polystyrene in cyclohexane were performed between the lower critical solution temperatures and 100 °C at several molecular weights. At the theta point, the hydrodynamic radii Rh followed the dependence Rh(Å)=0.24 M0.5z for z-average molecular weights Mz above ∼105. Below the theta point, the hydrodynamic radii contracted less sharply with decreasing temperature than the radii of gyration, reflecting the fact that excluded volume effects are more important for polymer segments separated by large distances. Polymer expansion above the theta point did not reach asymptotic values even at 100 °C for Mz below ∼4×105. Blob theory accounts qualitatively but not quantitatively for polymer contraction and swelling. The hydrodynamic expansion can be related to the excluded volume parameter with satisfactory agreement with the excluded volume theories.