Levich Institute Seminar Announcement, 09/21/2004

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Tuesday, 09/21/2004
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Kate Stebe
Johns Hopkins University
Department of Chemical and Biomolecular Engineering


"Surfactant Effects on Drop Detachment"

ABSTRACT


When a viscous drop detaches in a viscous fluid, it evolves to form a distended shape that detaches via the rapid formation and pinching of a neck. Typically, two necks form, a primary neck beneath the detaching drop, and a secondary neck just above the remnant drop. In the absence of surfactants, neck pinch-off occurs at the primary neck and displays self-similar dynamics that are governed locally by the balance of capillary and viscous stresses in creeping flow. For viscous drops surrounded by viscous liquids, this regime has been predicted by scaling arguments1, verified in experiment2 and studied using boundary integral simulations3. We study these effects numerically in the presence of surfactants in either the insoluble or adsorption-desorption limits.

In the absence of surfactants, the rate of surface dilatation is most negative just above the primary neck. When surfactants are present, they accumulate there. Since surface tension response is highly nonlinear at concentrations comparable to the maximum packing, regions of high surfactant packing have low local surface tensions and hence low capillary stresses. Necking dynamics are significantly altered. For example, for insoluble surfactants at high enough surface concentrations, drops break at the primary neck with new self-similar shapes featuring shallower slopes above and below the neck. For soluble surfactants, even more complexity emerges. Drops break at the primary neck at low surfactant coverage, at the secondary neck at moderate coverages, or fail to neck at elevated coverages, suggesting a transition from dripping to jetting modes.

1Lister J.R., Stone HA, Phys. Fluids 10, 2758 (1998)
2Cohen I., Nagel S.R., Phys. Fluids 13, 3533 (2001)
3Zhang W.W., Lister J.R., Phys. Rev. Lett. 83, 1151 (1999)

BRIEF ACADEMIC/EMPLOYMENT HISTORY
  • Education: Ph. D., Chemical Engineering, City University of New York (advisor: Charles Maldarelli), 1989; M. S., Chemical Engineering, City University of New York, 1989; B. A., City College of New York, 1984.
  • Professional Experience: The Johns Hopkins University, Department of Chemical and Biomolecular Engineering: Professor, 2000-present, Associate Professor, 1996-2000, Assistant Professor, 1991- 1996; Research Associate (advisor: D. Barthes-Biesel), 1989-1990, Adjunct Faculty, Department of Mathematics, City College of New York, 1985.
  • Joint appointment: Department of Biomedical Engineering; Secondary appointments: Department of Materials Science and Engineering; Department of Mechanical Engineering

CURRENT RESEARCH INTERESTS Surfactants and interfacial flows, Marangoni effects, dynamic surface tension, evaporative driven assembly of colloidal particles, patterned electrodeposition using self-assembled monolayers.