Researchers currently use all types of processes to try and create mixing, with only “mixed” success. “In small devices,” says Sandia materials scientist Jim Martin “people have tried all kinds of pillars and mixing cells to initiate mixing, but these approaches don’t work well.” Researchers need simpler and more reliable ways to mix in tiny places such as micrometer-sized channels, Martin said.
“Mixing liquids in tiny volumes,” Martin said, “is surprisingly difficult.” When fluid is pushed down a big pipe, eddies are generated that create mixing. But if fluid is pushed down a small pipe no eddies are generated and mixing does not occur unless you subject the fluid to tremendous pressure, which isn’t usually easy or feasible, he said.
Martin’s discovery of how to mix tiny liquid volumes arose from LDRD-funded research directed at improving the sensitivity of the chemical sensors developed in his lab. That project, “Field-Structured Composite Studies,” was a joint effort with Rod Williamson (now retired). While their LDRD project did not lead to the expected results, Martin and Williamson were surprised by the wide variety of physical effects they discovered along the way, including magnetic mixing. These effects, Martin said, ended up being much more interesting and important than the original goal. …
In the new method of mixing, when one turns on a particular kind of magnetic field, the magnetic particles suspended in the fluid form chains like strings of pearls. The chains start swirling around and that’s what does the mixing. The particles are then removed magnetically, leaving a nice mixed-up liquid.