(383c) Thermocapillary Induced Deformation and Breakup of Partially Engulfed Drops At Non-Zero Capillary Number

Compound drops are comprised of two or more immiscible phases, one of which entirely or partially engulfs the others. When such drops are embedded in a non-isothermal viscous fluid under gravity or in microgravity environment, they exhibit motion, deformation and possible break-up.

We study partially engulfed drops having two phases and demonstrate that, for linear temperature fields, the motion (even in the absence of gravity) may be in or, surprisingly, against the direction of the temperature gradient. The direction of the motion depends on various physical parameters such as the volume and viscosity ratios of the drop phases and, in particular, relative variations in the surface tensions of the drop interfaces due to the temperature. The deformation of the drop interfaces is calculated for small capillary numbers at creeping flow and for several cases: hydrostatics, motion in isothermal gravity field and thermocaillary induced motion.

Special attention is given to the three phase contact line and the associated contact angles. The change of these angles with small capillary numbers is only a second order effect. However, major effects are anticipated due to the thermocapillary migration. Thus, considerable shape variations are obtained even in cases where the interfacial segments maintain static shapes, and they lead to rearrangement of the drop phases. This rearrangement depends mostly on the direction of the migration along the temperature field. We present cases in which the compound drop evolves from being partially engulfed to completely engulfed, and in which the compound drop disintegrates and the phases separate into individual daughter drops.