Lubricated optical rheometer for the study of two-dimensional complex flows of polymer melts

• Published in: Journal of non-Newtonian fluid mechanics Vol. 150; no. 1; pp. 43 - 55
• Main Authors: Soulages, J., Schweizer, T., Venerus, D.C., Hostettler, J., Mettler, F., Kröger, M., Öttinger, H.C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 14.03.2008; Elsevier
• Subjects: Applied sciences; End effects; Exact sciences and technology; Flow-induced birefringence; Lubrication; Particle tracking velocimetry; Physical properties; Polymer industry, paints, wood; Polymer melt; Properties and testing; Rheological properties; Stagnation flow; Technology of polymers; Testing and control; Two-dimensional flow; Particle tracking velocimetry; Flow-induced birefringence; Stagnation flow; Two-dimensional flow; Polymer melt; End effects; Lubrication; Viscoelasticity; Isothermal flow; Molten state; Shear flow; Two dimensional flow; Experimental study; Low density ethylene polymer; Flow birefringence; Optical properties; Olefin polymer; Measurement method; Elongational flow; Rheometer; Rheological properties
• ISSN: 0377-0257; 1873-2631
• DOI: 10.1016/j.jnnfm.2007.10.006

We describe a novel optical cross-slot channel rheometer generating two-dimensional and isothermal complex flows of polymer melts. This is made possible by lubricating the channel front and back viewing windows. Flow-induced birefringence and particle tracking velocimetry are reviewed and used to investigate the cross-slot flow of a low density polyethylene melt involving mixed shear and planar extensional deformations. This new device solves the issue of end effects in flow birefringence experiments where no variations of the optical properties along the light path are expected. It greatly facilitates the interpretation of stress field data by providing reliable measurements of the polymer melt extinction angle χ and retardation δ , with a spatial resolution of one tenth of a millimeter. At the same time, it offers an enhanced temperature control and an increased optical accuracy due to an improved laser beam shaping. The capabilities and performances of this unique type of lubricated rheometer are discussed in detail and compared with previous approaches.