  This study focuses on comparing the individual polymer chain dynamics in an
entangled polymeric liquid under different shear and extension rates. Polymer
chains under various shear rates and extension rates were simulated using a
stochastic-tube model [J. Rheol. 56: 1057 (2012)]. We developed a Matlab code
to visualize and analyze the simulated configurations from the stochastic-tube
model. We introduced new variables to determine how the extent of linearity
changes with time for different shear rates, which is more useful than a
typical end-to-end distance analysis. We identified whether the polymer chains
undergo a tumbling rotation (slight elongation not accompanying contraction) or
flipping rotation (elongation accompanying contraction). The simulation results
indicate that the polymer chains exhibit a significant tendency to elongate at
higher shear rates and occasionally experience flipping, while lower shear
rates tend to exhibit very frequent tumbling. Furthermore, no rotations were
observed under extensional flows. These results help clarifying uncertainty of
previously proposed polymer deformation mechanisms of the convective constraint
release and the configuration-dependent friction coefficient.
