Rotational barriers and chain dynamics

Abstract

Internal viscosity, or the high-frequency viscous dissipation in polymer dynamics originating from the rotational energy barriers around skeletal bonds, is basically attributed to hindrance against the motion of conformational changes along the chain contour. The non-equilibrium statistical-mechanical background of the theory is discussed. Comparison between calculations and experimental results of the complex modulus and of the optical flow birefringence from polystyrene solutions under alternating shear stress is discussed. The best-fitting value of the characteristic time for bond rotation τ0, i.e., the only parameter required for internal viscosity, is in good agreement with the results of NMR, ESR and dielectric relaxation experiments.