8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P9.60Tue 611:23-14:00Signature of the presence of long chain branches on theflow kinematics and stress field in a cross-slot channelMonirosadat Sadati, 1 Clarisse Luap, 1 Martin Kröger, 1 and Hans ChristianÖttinger 11 ETH Zürich, Polymer Institute, Materials Dep. ETH Zürich, Wolfgang-Pauli Str. 10, 8093,Zürich, SwitzerlandA lubricated cross-slot channel rheometer producing strong extensional deformation in the stagnationregion has been utilized to study the complex flow behavior of a highly branched polyethylenemelt. The 2D kinematics of the complex flow was obtained using particle tracking velocimetry.Subsequently, from these noisy experimental velocimetry data, a reliable full field kinematics wasreconstructed by implementing a regularization based on the Tikhonov approach and a high orderfinite element approximation [1, 2]. In addition, the stress field was measured experimentallyusing flow induced birefringence. Results show that the presence of long chain branches in thepolymer structure generates high stress values near the outflow centerline influencing both the flowkinematics and the birefringence pattern. Moreover, the stress field was calculated by solving theeXtended Pom-Pom (XPP) constitutive equation [3] using the regularized experimental flow kinematicsthrough integration over streamlines. Comparison between the XPP cross-slot predictionsand experimental results elucidates that although the model is able to provide overall good quantitativematch, it fails to capture important details characteristic of the branched structure of the melt.[1] M. Sadati, C. Luap, M. Kröger, A. A. Gusev, H. C. Öttinger, J. Rheol. 55, 353 (2011).[2] M. Sadati, C. Luap, M. Kröger, H. C. Öttinger, J. Rheol. Submitted.[3] W. M. H. Verbeeten, G. W. M. Peters, F. P. T Baaijens, J. Non-Newtonian Fluid Mech. 108,301 (2002).60