Making Multicomponent Drops

We make water drops in oil by using the "flow focusing" geometry which was first introduced in microfluidics by Howard Stone's group at Harvard University. Two oil streams laterally "focus" a water stream into a narrow orifice producing a drop break-up at the exit of it. Different drop break-up regimes are observed in function of the relative oil to water flow rates. The resulting drop sizes range in the micron scale. (S.L. Anna, N. Bontoux, H.A. Stone. Appl.Phys.Lett. 82, 364 (2003)).

In order to make multicomponent drops, we added a new step to the stream of the dispersed phase (water). Two miscible fluids (A and B) merge at a junction and coflow. As the flows are laminar there is no mixing, and if there is, this is only by diffusion. The A-B coflow (in the picture A-B-A) is emulsified at the flow focusing junction and multicomponent A+B drops are formed. The volume fraction of each of the two fluids can be continuously tuned by variying the A and B flow rates.

Example of a multicomponent drop break-up. The A-B-A coflow is emulsified at the flow focusing junction. Fluid A is water and fluid B is a colloidal suspension of 1 micron diameter polystyrene beads in water at 0.5 wt%. Colloids are used as flow tracers. The oil is a 20 cp viscosity silicon oil. In order to make droplet confined chemical reactions we coflow three fluids A-B-C where fluid A and C chemically react and where fluid B is a "neutral spacer" prevent the reaction start in the coflow. We have succeed confined silica gelation by combining a Ludox solution (Fluid A) and a solution of Magnesium Chloride (Fluid C). Fluid B was water.

This web page is maintained by:

Galder Cristobal-Azkarate
9 & 15 Oxford Street
Gordon McKay Laboratory, Room #519
Cambridge, MA 02138
617 496 9562

Last update 07/05/03

This work is in collaboration with