SOME TESTS OF CONSTITUTIVE-EQUATIONS FOR ENTANGLED POLYMERS BASED ON PLANAR-EXTENSION FLOW HISTORIES IN A PERIODICALLY CONSTRICTED CHANNEL

Stress and velocity were determined locally by birefringence measureme nts and laser Doppler velocimetry for a mildly entangled polystyrene s olution flowing at steady state in a rectangular channel with sinusoid ally varying wall spacing. Having measured both the velocity and stres s fields, we were able to test constitutive equations locally, i.e., w ithout solving the equations of motion for the entire flow. Four were examined for the periodic planar extensions on the channel centerplane : the Newtonian model, the Lodge network model, the Doi-Edwards tube m odel, and the Wagner-Schaeffer modification of Doi-Edwards. High enoug h Weissenberg and Deborah numbers were reached to produce sizable depa rtures from the Newtonian predictions. The Doi-Edwards model underpred icted the stress, as did Wagner-Schaeffer, although to a lesser extent . Predictions of the Lodge model were best of all, a surprising result in view of its inadequacy for simple shear deformations. The predicti ons of the Lodge model, without parameter adjustment, agreed remarkabl y well with the planar extension data over the accessible range for ou r apparatus: Deborah numbers up to 2.0, extensional Weissenberg number s up to 6.5, and a maximum extension ratio of about 2.3.