Planar Elongation Flow Analysis of Non-Newtonian Fluids Using a Disk-Shaped Bob

Abstract

Planar elongation viscosity is a material property involved in extensional deformation, which plays a significant role in many processes such as film-casting and coating. As for the elongation behavior of a polymeric film, some commercial measurement methods are available. However, these measurement methods cannot be applied to liquids with lower viscosities. A method of measuring planar elongation viscosity, especially for low viscosity liquids, has been proposed, which generates a planar elongation flow by pushing a bullet-shaped bob into a cup filled with the sample liquid. The pushing force, which can be measured by a conventional rheometer, reflects the responses of shear, planar extensional deformation, and buoyancy. However, measurements using a bulletshaped bob may be strongly affected by the shear flow between the bob and the cup. Therefore, an alternative measurement using a flat disk-shaped bob is proposed, in order to significantly reduce the influence of shear flow. However, such improvements cannot be estimated numerically. In this study, we performed numerical simulations of viscoelastic fluids for both measurement methods to clarify the shear flow effects.