The "Open Syphon" or "Fano Flow"

In this video clip a dilute (0.025 wt%) solutionof a high molecular weight (2106 g/mol) polystyrene polymer (Polysciences Inc) is dissolved in a low molecular weight (~100 g/mol) newtonian viscous (~20 Pa.s) solvent (Piccolastic, Hercules Inc).

The rotating drum seen at the start of the clip continues to rotate throughout the presentation.  The elastic stresses stored in the fluid by the long relaxation times of the extended polymer molecules allows the fluid to "strain harden" in extension. The video clearly shows that, beyond the initial "collection region", the filament is of a constant radius as the strain hardening prevents the filament "necking down", a primary form of failure in the spinning of simpler fluids. This effect can be utilised to understand, and improve, the commercial spinning of threads and fibres.  A Newtonian fluid would not be capable of this behaviour.

open_syphon.avi (0.90 MB) (1.89 MB) (12.7 MB) (2.80 MB)