F. V. Chávez, K. Saalwächter.
NMR Observation of Entangled
Polymer Dynamics: Tube Model Predictions and Constraint Release.
Rev. Lett. 104, 198305 (2010). DOI 10.1103/PhysRevLett.104.198305.
We use a benchtop NMR technique to monitor entangled polymer melt dynamics over
5 decades in time covering regimes II–IV of the tube model. We confirm the
familiar molar mass scaling exponents of the regime transitions, but we observe
a mass-dependent time scaling exponent describing segmental fluctuations in the
constrained-Rouse regime II up to high molecular weights. Local chain motions
are thus governed by modes that are much less restricted than predicted by the
tube model. Diluting protonated chains in deuterated invisible matrix chains, we
prove that the exponent is determined by the matrix molecular weight, suggesting
constraint-release effects as the origin.