ISSN:
0887-6266
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Flow-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.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/polb.1987.090251101
