An Inter-laboratory Comparison of Measurements from 
Filament-Stretching Rheometers Using Common Test Fluids

Shelley L. Anna
Division of Engineering and Applied Sciences, Harvard University Cambridge, MA 02138 U.S.A.

Gareth H. McKinley
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Duc A. Nguyen and Tam Sridhar
Department of Chemical Engineering, Monash University Clayton, Victoria, AUSTRALIA.

Susan J. Muller
Department of Chemical Engineering, University of California - Berkeley and Lawrence Berkeley National Laboratory Berkeley, CA 94720 U.S.A.

Jin Huang and David F. James
Department of Mechanical and Industrial Engineering, University of Toronto Toronto M5S 3G8 CANADA


Following development of a filament-stretching extensional rheometer at Monash University, similar rheometers have been designed and built in other laboratories. To help validate the basic technique, a collaborative program was undertaken to compare results from several instruments. First, three test fluids prepared at the University of California at Berkeley were characterized in steady and transient shear flows there and at the Massachusetts Institute of Technology, and then tested in extensional rheometers at M.I.T., Monash and the University of Toronto. Each fluid is a constant-viscosity solution of narrow-molecular-weight-distribution polystyrene dissolved in oligomeric polystyrene. The solute molecular weights are 2.0, 6.5, and 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 seconds respectively. The scaling of relaxation times with molecular weight indicates better than theta solvent quality, a finding consistent with independent intrinsic viscometry measurements of equilibrium coil size. Each fluid was tested in the three filament stretching rheometers at similar Deborah numbers. Despite variations in instrument design and the general difficulty of the technique, transient Trouton ratios measured in the three instruments are shown to agree quantitatively.

Keywords: Transient extensional rheology, filament stretching device, rheometry, Boger fluids, dilute polymer solutions. 

Published  J. Rheol., 45(1), 2001, p 83-114.