Effect of a controlled
pre-deformation history on extensional viscosity of dilute polymer
solutions

by Shelley L. Anna and Gareth H. McKinley

We use a modified filament stretching rheometer to quantify the
influence of a known controlled pre-shear history on the transient
extensional viscosity of a dilute polymer solution. Two different types
of pre-deformation are explored; both influence the subsequent
stretching significantly, albeit in opposite ways. Small-amplitude
oscillatory straining parallel to the direction of stretching enhances
strain hardening and accelerates the tensile stress growth toward the
steady-state value. Conversely, steady torsional shearing orthogonal to
the direction of stretching retards strain hardening and results in a
delayed approach to steady-state elongational flow. In both cases, the
final steady-state extensional viscosity is the same as that observed
with no pre-shearing. Calculations using a finitely extensible
nonlinear elastic Peterlin dumbbell model qualitatively capture the
trends observed in experiments, enabling interpretation of these
observations in terms of the degree of polymer chain stretching imposed
by the flow before extensional stretching.