The observation and evaluation of extensional filament deformation and breakup profiles for Non Newtonian fluids using a high strain rate double piston apparatus

- A new fast filament stretching apparatus.
- Capable of extensional strain rates exceeding 1000 s−1.
- Range of fluids tested.
- Deformation and breakup profiles reported.
- Some matching of experimental profiles with numerical simulation.

SummaryThis paper reports a new design of experimental double piston filament stretching apparatus that can stretch fluids to very high extensional strain rates. Using high speed photography, filament deformation and breakup profiles of a strategically selected range of fluids including low and higher viscosity Newtonian liquids together with a viscoelastic polymer solution, biological and yield stress fluids were tested for the first time at extensional strain rates in excess of 1000 s−1. The stretching rate was sufficiently high that observation of low viscosity Newtonian fluid stretching, end pinching and break was observed during the stretching period of the deformation, whereas for a higher Newtonian viscosity, filament thinning and breakup occurred after the cessation of piston movement. Different fluid rheologies resulted in very different thinning and breakup profiles and the kinetics, in particular of yield stress fluids showed a striking contrast to Newtonians or viscoelastic fluids. Surprisingly all the tested fluids had an initial sub millisecond “wine glass” profile of deformation which could be approximately captured using a simple parabolic mass balance equation. Subsequent deformation profiles were however very sensitive to the rheology of the test fluid and where the final breakup occurred before or after piston cessation. In certain cases the thinning and break up was successfully matched with a 1D numerical simulation demonstrating the way numerical modelling can be used with the fluids correct rheological characterization to gain physical insight into how rheologically complex fluids deform and breakup at very high extensional deformation rates.