Dynamics at the Temperature Crossover in Dilute Polymer Solutions Investigated by Neutron Spin-Echo Spectroscopy

Applying ultrahigh-resolution neutron spin-echo spectroscopy the existence of a $q$-dependent temperature crossover in the dynamics of dilute polymer solutions was proved. It is associated with the transition from $\theta$ to good solvent conditions. At small momentum transfers $q$ a nearly stepwise increase of the reduced quasielastic linewidth versus the reduced temperature was observed. With increasing $q$, both the sharpness of the transition and the step height decrease.