Thermodynamical approach to polymer rheology

The model of pseudocrosslink is extended to polymer rheology. There exist various sizes b of 4–16 between transition points A and B . Each link is connected with a chain having length n b and relaxation time τ b . n b is equal to b 2 and τ b is proportional to n b 2 . A, B , and C (polymer terminal) divide the stress‐relaxation spectrum into four zones. In the AB zone, successive dissociation of links occurs from a small size to a large one and rigidity G is decreased with time t as G ∝ t −0.5 and viscosity η is increased as G ∝ t 0.5 . In the BC zone, dissociation of the B link proceeds along a molecule of length n in a mode of squeezing of molecule and η becomes constant, but G still decreases due to increase of unperturbed end‐to‐end distance of chain and G ∝ t −0.5 . However, dynamic elasticity becomes constant due to a small amplitude. At high shear, links are loosened and G and η are much decreased. Beyond C , molecule flows and η increases as η ∝ γ −0.8 n 3.5 , but high shear rate γ diminishes the effect of n due to extension of the molecule. Extensional viscosity η * is affected by the change of shape as η * ∝ t 1.5 and gives an overshoot. Under load, creep occurs and it is proportional to t 1/2–1/3 . © 1995 John Wiley & Sons, Inc.