Jolts mix micro fluids

Researchers working on chips that mix small amounts of liquids have more of a challenge than at first meets the eye. At the very small scale, blending liquids is more like kneeding dough than mixing cream into coffee.

Researchers from the New Jersey Institute of Technology have shown that it is possible to mix small amounts of liquids more quickly by pulsing the flow rates of the liquids through the channels in such a way that the pulse rates of the two liquids are out of phase.

The researchers demonstrated the method using a "T" channel intersection whose segments were 200 microns wide by 120 microns deep, or about twice the circumference of a human hair.

The out-of-phase pulsing caused the interface between the two liquids to stretch, fold and sweep through the liquids, causing them to mix after traveling about two millimeters down the channel, which took about one second.

The mixing method is appropriate for any lab-on-a-chip that uses mechanical pumps to control fluid flow, and could be used in practical devices within a few years, according to the researchers. The work appeared in the May 19, 2003 issue of Lab on a Chip.