Eine rheo-optische Apparatur für die Durchführung homogener,einfacher Dehnungen an Polymerschmelzen mit simultaner Aufzeichnung der Deformation,der mechanischen Spannung und der Doppelbrechung

The present paper describes a rheo-optical apparatus consisting of an elongational rheometer (with rotary clamps) and a device to measure birefringence. This equipment was designed to perform homogeneous deformations on polymer melts in the simple elongational mode. Elongational experiments were performed on polyisobutylene samples at room temperature using different strain rates (from \documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document} 0.01 s^?1 to 1 s^?1). In typical experiments homogeneous elongations up to λ ≈ 200 and stresses up to 2 · 10⁶ Pa were achieved. The stress, the birefringence, and the deformation were obtained by measuring the force, the sample thickness, the optical retardation (the frequency of the sampling was 20 Hz) and the width of the sample (the frequency of the sampling was 3 Hz). It was found that the stress-optical coefficient was constant. The homogeneity of the deformations was carefully controlled because inhomogeneities cause serious errors in the measurements of elongational viscosity and birefringence.