TY - JOUR
T1 - Drop pinch-off and filament dynamics of wormlike micellar fluids
AU - Smolka, Linda B.
AU - Belmonte, Andrew
N1 - Funding Information:
We would like to thank G. McKinley, N.Z. Handzy, and T. Podgorski for enlightening discussions, and A. Bernoff, J.-F. Berret, G. Forest, D.M. Henderson, and M.J. Shelley for helpful comments. AB acknowledges the support of the A.P. Sloan Foundation and National Science Foundation (CAREER Award DMR-0094167). LBS acknowledges the support of the National Science Foundation (VIGRE grant DMS-9983320, and partial support from DMS-0074049) while at Duke University.
PY - 2003/10/20
Y1 - 2003/10/20
N2 - Observations are presented of several novel phenomena involved in the dynamics of a pendant drop of viscoelastic micellar fluid falling through air. Generally, when a drop falls a filament forms connecting it to the orifice; the filament eventually breaks due to an instability. The filament dynamics and instabilities reported here are very different from the standard Newtonian and non-Newtonian cases. At low surfactant 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 produced. 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. We investigate this stall by generalizing Keiller's simple model for filament motion [J. Non-Newtonian Fluid Mech. 42 (1992) 37], using instead the FENE-CR constitutive equation. Numerical simulations of this model indicate that stall occurs in the range of low solvent viscosity, high elasticity, and high molecular weight. At the highest concentrations, we observe a surface "blistering" instability along the filament long before pinch-off occurs.
AB - Observations are presented of several novel phenomena involved in the dynamics of a pendant drop of viscoelastic micellar fluid falling through air. Generally, when a drop falls a filament forms connecting it to the orifice; the filament eventually breaks due to an instability. The filament dynamics and instabilities reported here are very different from the standard Newtonian and non-Newtonian cases. At low surfactant 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 produced. 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. We investigate this stall by generalizing Keiller's simple model for filament motion [J. Non-Newtonian Fluid Mech. 42 (1992) 37], using instead the FENE-CR constitutive equation. Numerical simulations of this model indicate that stall occurs in the range of low solvent viscosity, high elasticity, and high molecular weight. At the highest concentrations, we observe a surface "blistering" instability along the filament long before pinch-off occurs.
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U2 - 10.1016/S0377-0257(03)00116-2
DO - 10.1016/S0377-0257(03)00116-2
M3 - Article
AN - SCOPUS:0142104243
SN - 0377-0257
VL - 115
SP - 1
EP - 25
JO - Journal of Non-Newtonian Fluid Mechanics
JF - Journal of Non-Newtonian Fluid Mechanics
IS - 1
ER -