(Dr. Paul Neitzel, advisor)

"Steady Thermocapillary Flow Between a Noncoalescing Liquid Droplet and a Solid Surface"

Abstract

Noncoalescence can be observed between two differently heated drops of a low viscosity liquid such as silicone oil.  This occurs as a result of thermocapillary and Marangoni convection.  The convection produces surface motion that leads to bulk flow in both the drops and the surrounding gas.  The gas flows between the two drops creating a lubricating gas film which maintains separation.  Noncoalescence has also been shown to occur in a liquid at ambient temperature when a drop is brought into contact with a rotating bath.  This is similar to the classic slider-bearing problem.  In addition, it occurs between a drop and a stagnant bath with an applied temperature gradient.

The phenomenon of noncoalescence could have some interesting applications in a microgravity environment.  Bearing for small loads could be formed from the noncoalescing drops.  These bearing would be smooth, self-centering and almost frictionless.  Other applications might include measuring loads, measuring attractive forces between liquid surfaces, and enhancing the separation process.

Since noncoalescence is a result of gas lubrication, the interaction between a liquid drop and a solid surface is studied to further understand this phenomenon.  In the problem model, a thin, two-dimensional liquid drop is pressed against a colder solid surface.  The equations governing the liquid and the gas behavior are simplified using lubrication theory.  The system includes the effects of surface tension, thermocapillarity, viscosity, and no-slip boundary conditions.  The effects of gravity are not considered since applications for noncoalescence occur in a microgravity environment.  A steady state solution is determined to convey the behavior on the drop and the surrounding gas and examine the formation of a dimple at the drop’s center.