February 14, 2003 Colloquium

Microfluidic devices have been used to make inverse emulsions of water droplets in oil with a very narrow size distribution. The emulsification process and movement of drops in the oil stream is observed by high speed video and flow patterns within individual droplets are monitored with colloidal tracer particles. Passive schemes to control droplet breakup have been developed and the physical mechanism by which drops break in an extensional flow created at a microchannel T-junction has been understood. These observations in simple fluids provide insight into the topological changes that take place in nematic liquid crystal droplets under similar flow conditions.