AN EXPLANATION OF THE RHEOLOGICAL PROPERTIES OF BOGER FLUIDS

The suitability of the Oldroyd-B model for these fluids is examined. In the present experiments, the fluids were made by first dissolving high molecular weight polyisobutylene in kerosene, then adding poly (1-butene) to the solution. The failure of the Oldroyd-B model (Hookean dumbbell suspended in a Newtonian carrier fluid) to describe the behavior of Boger fluids in oscillatory flow was found to be due to the solvent possessing a slight amount of elasticity. The elasticity of the solvent is measurable only at high frequencies and expressed as a relaxation time is on the order of 10** minus **4 s while that of the polymer is 10** minus **1 s. Including this small amount of elasticity in a rheological model predicts the oscillatory material properties based on parameters obtained from separate rheological data.