Eur. Phys. J. E (2009) 30: 37-41
https://doi.org/10.1140/epje/i2009-10503-x

Regular Article

Elasticity of polymer solutions in Couette flow measured by fluorescence resonance energy transfer (FRET)

¹ Department of Chemical and Biomolecular Engineering, University of Melbourne, 3010, Melbourne, VIC, Australia
² CSIRO Molecular and Health Technologies, Bag 10, Clayton South, 3169, Victoria, Australia

^* e-mail: davided@unimelb.edu.au

Received: 25 August 2008
Revised: 10 May 2009
Accepted: 29 July 2009
Published online: 15 September 2009

Abstract

Polymer solutions are complex fluids that show elasticity and deformation in response to shear flows. A fluorescence resonance energy transfer (FRET) technique has been applied to measure the end-to-end distances of individual polymer molecules in Couette flow, using end-tagged reversible-addition fragmentation chain transfer (RAFT) polymerised poly(methyl methacrylate) (PMMA). Real-time rheofluorescence measurements on these polymers in solution above the critical overlap concentration are reported at several shear rates. The PMMA in Couette flow shows a systematic decrease in fluorescence, corresponding to a reduction in end-to-end distance of the polymer molecules with shear exposure. Full reversibility of the fluorescence signal is observed after the cessation of shear. These results show that polymer solution elasticity arises from compressive deformation of the polymer molecules in Couette flow. At polymer concentrations above the critical overlap, the polymer molecules are restricted by their neighbours and the net hydrodynamic forces are compressive rather than extensive.