Dynamics of Polymer Rings in Ring-Linear Blends by Neutron Spin Echo Spectroscopy

We present a microscopic investigation of the polyethylene-oxide (PEO) ring dynamics in symmetric ring-linear blends with a molecular weight of 40 kg/mol over the full concentration range. Applying neutron spin echo (NSE) spectroscopy on samples containing a fraction of labeled rings, we observe the internal ring dynamics and its modifications as a function of ring volume fraction ϕR. With increasing linear composition, a dynamic cross over from self-similar ring-like relaxation to local reptation-like dynamics is observed. At ϕR = 0.5, where the blend viscosity exhibits its maximum, the spectral shapes change from ring- to local reptation-type dynamics, even though the enacted constraints are weaker than those in the linear melt. For ϕR ≤ 0.35, the ring motion is completely enslaved by the linear host.