An interlaboratory comparison of measurements from filament-stretching rheometers using common test fluids

Following development of a filament-stretching extensional rheometer at Mon ash University, similar rheometers have been designed and built in other la boratories. To help validate the basic technique, a collaborative program w as undertaken to compare results from several instruments. First, three tes t fluids prepared at the University of California at Berkeley were characte rized in steady and transient shear flows there and at the Massachusetts In stitute of Technology (M.I.T.), and then tested in extensional rheometers a t M.I.T., Monash and the University of Toronto. Each fluid is a constant-vi scosity solution of narrow-molecuIar-weight-distribution polystyrene dissol ved in oligomeric polystyrene. The solute molecular weights are 2.0, 6.5, a nd 20 million g/mol, and the polymer concentration in each fluid is 0.05 wt .%. From linear viscoelastic measurements, the Zimm relaxation times of the fluids are found to be 3.7, 31, and 150 s, respectively. The scaling of re laxation times with molecular weight indicates better-than-theta solvent qu ality, a finding consistent with independent intrinsic viscometry measureme nts of equilibrium coil size. Each fluid was tested in the three filament s tretching rheometers at similar Deborah numbers. Despite variations in inst rument design and the general difficulty of the technique, transient Trouto n ratios measured in the three instruments are shown to agree quantitativel y. (C) 2001 The Society of Rheology.