Staff profile
Publication details for Prof Tom McLeish
Auhl, D. Hoyle, D.M. Hassell, D. Lord, T.D. Mackley, M.R. Harlen, O.G. & McLeish, T.C.B. (2011). Cross-slot extensional rheometry and the steady-state extensional response of long chain branched polymer melts. Journal of Rheology 55(4): 875-900.- Publication type: Journal papers: academic
- ISSN/ISBN: 0148-6055 (print)
- DOI: 10.1122/1.3589972
- View online: Online version
- Durham research online: DRO record
Author(s) from Durham
Abstract
Stress-optical measurements at a flow stagnation point in confined geometries such as the cross-slot provide an elegant way to perform extensional testing for polymer melts. This technique is especially useful for samples which have a steady-state that cannot be reached (easily) in standard elongational rheometry, for example, highly branched polymers which show a non-homogeneous deformation that occurs in stretching experiments for Hencky strains above 4. In contrast to filament stretching, the cross-slot provides one point at which steady-state extensional flow may be sustained indefinitely. In this study, a Cambridge multi-pass rheometer [ Coventry, K. D., and M. R. Mackley, J. Rheol. 52, 401–415 (2008) ] is used to generate planar elongational flow in a cross-slot geometry for different polyethylene melts. The experimental results are compared to finite element flow simulations using the multi-mode Pompom constitutive equations. The steady-state elongational viscosity at the stagnation point is computed from the flow-induced stress birefringence and the strain-rate determined from numerical calculations of the flow field. We apply this technique to a range of different branched high- and low-density polyethylene melts. This demonstrates both the effectiveness of this technique and shows how the stress distribution in a complex flow depends on molecular structure. Cross slot extensional rheometry therefore provides a very promising technique for parameterizing molecular constitutive equations for LCB melts.