FLOW BIREFRINGENCE STUDIES IN TRANSIENT FLOWS OF A 2 ROLL MILL FOR THE TEST-FLUID M1

We have studied the test-fluid M1 in flows generated by a two-roll mill. These flows are linear, and two-dimensional, and the magnitudes of the strain-rates are greater than the vorticity. The polymeric solution is shown to degrade significantly, even for small values of the velocity gradient, as measured by the changes in the macroscopic relaxation time-scales. Consequently, the determination of macroscopic properties such as elongational viscosity based upon the overall pressure difference, or the total force as measured in a spin-line rheometer, may not be representative of the properties of the fresh, undegraded fluid. In this work, the degradation of the test-fluid has been studied as a function of the strength of the velocity gradient for different values of the ratio of the strain-rate to vorticity of the flow. Furthermore, the observed relaxation time-scales have been evaluated based on data for steady state flows, and several transient flow histories such as start-up and cessation of flows, and double-step flows. These flow histories provide us with some insight into the relaxation dynamics of the polymeric structure for different initial conformation states. © 1990.