Flow Birefringence and Velocity Measurements for Polymer Melts in a Cross-Slot Flow Channel

A dissertation submitted to ETH Zürich for the degree of Doctor of Natural Sciences. 2007. – 197 p.The goal of this thesis is to develop a new isothermal lubricated cross-slot channel rheometer capable of creating two-dimensional (2D) complex flows of combined shear and planar elongation. In this work, the birefringence and velocity data are derived from flowinduced birefringence and particle tracking velocimetry measurements, respectively. For the study of complex flows of birefringent polymermelts, end effects cannot be eliminated by increasing the aspect ratio of the experimental geometry. Consequently, the channel front and back viewing windows are lubricated to guarantee the absence of variations of the optical properties along the light path. This allows us to work with an aspect ratio of 0.5 which further offers enhanced temperature control and increased optical accuracy due to an improved laser beam shaping.