Papers Published
Abstract:
Observations are presented of several novel phenomena
involved in the dynamics of a falling drop of
viscoelastic micellar fluid. At low concentration, the
cylindrical filament necks down and pinches off rapidly
(~ 10 ms) at one location along the filament. After
pinch-off the free filament ends retract and no satellite
drops are formed. At higher concentrations, the pinch-off
also occurs along the filament, but in a more gradual
process (~ 1 s). Furthermore, the free filament ends do not
fully retract, instead retaining some of their deformation.
The falling drop is also observed to slow or even stop
(stall) before pinch-off, indicating that sufficient
elastic stress has built up to balance its weight. A
detailed study of a simple model for the filament using
the FENE-CR constitutive equation indicates that this
stall occurs in the range of low solvent viscosity, high
elasticity, and high molecular weight. At the highest
concentrations a surface ``blistering'' instability is
seen along the filament long before pinch-off occurs.