Mechanical and optical measurements of planar elongational viscosity with two-dimensional opposing jets nozzle elongational rheometer

Abstract

The technique to measure planar elongation viscosity from both mechanical and optical measurements by using two-dimensional opposing jets nozzle flow has been developed. This technique generates planar elongational flow between both nozzles and simultaneously measures reaction force acting on the nozzle and flow birefringence at the stagnation point. The correctness of elongational viscosity measured by this technique was verified from experimental results for Newtonian fluid and Maxwell fluid. Starch syrup aqueous solution and CTAB/NaSal surfactant solution are used for the Newtonian fluid and the Maxwell fluid respectively. As the results, transient behavior of nozzle reaction force and flow birefringence for Maxwell fluid show good agreement. It indicates that this technique can evaluate planar elongation viscosity for not only fluids that obey stress-optical rule but also fluids have flow birefringence property. In addition, Trouton ratio of optical results become 4 and it indicates the results from optical technique are accurate. On the other hand, the data from mechanical technique provide Trouton ratio with range 15 to 20. Trouton ratio of Newtonian fluid also shows 10 ~ 20 and these results conclude that mechanical data should be limited for qualitative evaluation. However, Trouton ratio of mechanical technique is independent from sample viscosity and elongaitonal rate. Therefore, it can provide quantitatively valuable result by using correction factor.

Keywords

• elongational rheometry
• planar elongational flow
• two-dimensional opposing jet flow
• flow birefringence
• viscoelastic fluid