Structural changes during elongation of polymer solutions

Abstract

During elongational flow experiments on polymer solutions certain anomalous examples of flow behaviour have been noted. These are, 1. (1) a non uniform velocity profile in the radial direction in strongly non-Newtonian fluids being elongated at high rates. 2. (2) the loss of tack in the filament as rate of elongation increased, 3. (3) the bouncing of the filament off a rotating drum at high elongation rates, and 4. (4) the development of sustained rubber-like lateral vibrations in the fluids elongated at high rate. In addition, droplet formation occurred on the surface of the solutions which were elongated rapidly then suddenly stopped. Photography showed that the filaments continued through these droplets. When captured and dried, it was observed that the filament contained the bulk of the solute. The droplets appeared to have only a low concentration of polymer. On the basis of the photographic evidence and the thermodynamics of complex formation between elongated polymer chains, it would appear that complexation of the chains is occurring at high elongation rates. This could partly account for the strain hardening encountered during elongation of many polymeric fluids. Where solubility parameter difference between polymer and solvent was large, the complex formed could come out of solution forming a gel and a solvent rich phase.