Abstract
AbstractFlow‐induced changes in the conformation of polymer molecules in dilute polyelectrolyte solutions were studied, using birefringence techniques, as a function of molecular weight and added salt concentration in laminar, two‐dimensional extensional flows produced in four‐ and two‐roll mills. Overshoots in the flow birefringence during startup of simple‐shear flow are presented. Of particular interest is the so‐called coil‐stretch transition. It is shown that the electrostatic expansion of the polyelectrolyte has a dramatic effect on the onset shear rate for the coil‐stretch transition and also on the shape of the flow birefringence versus shear rate curves during the stretching process. A reasonable description of the coil‐stretch transition and its dependence on equilibrium configuration is obtained theoretically using a charged dumbbell model with conformation‐dependent bead friction. Being dependent on the longest relaxation time of the polymer, and therefore not too sensitive to intramolecular details, the dumbbell model can be applied in two ways: either using a charge force to expand its rest state or reducing N, the number of Kuhn segments, in proportion to the increase in relaxation time of the expanded polyelectrolyte.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call