Preliminary investigation of elongational flow of dilute polymer solutions

Abstract

A tubeless siphon apparatus has been set up to measure extensional flow. In this apparatus the liquid is continuously drawn into a capillary and, after steady flow has been established, the tube is raised above the liquid surface. With viscoelastic liquids the flow continues and a column can be lifted from the reservoir. At the capillary entrance an oscillating bead of excess liquid collects, which interferes both with the flow and the measurements. This can be minimized by careful control of the liquid column height. For homogeneous solutions the column is symmetrical and tapers steadily from the liquid surface to the capillary entrance, with no bulging. Preliminary results show tensile viscosities 10³ times that of the Trouton coefficient 3η_S0, where η_S0 is the zeroshear‐Rate shear viscosity, and having a very strong dependence on deformation rate. A concentration‐stretch‐rate‐reduced variable scheme is proposed.