A team of researchers from the University of Massachusetts Amherst and the University of California, Los Angeles (UCLA) has developed a new, simple method of manipulating small droplets on a hydrophilic surface. This new strategy is described in a paper published in the journal “Nature.”
The team includes Tingyi “Leo” Liu, assistant professor of mechanical and industrial engineering at UMass Amherst. Liu is head of the Interdisciplinary Interface Engineering Laboratory (Inter²EngrLAB) in the College of Engineering.
Liu says the new method reverses what scientists already know about a phenomenon called electrowetting, where droplets of liquid are attracted to and spread on a conductive surface in response to an applied voltage. Despite being known for more than a century, electrowetting generally requires additional coatings to make it practical for applications, he says. Such a modified configuration of electrowetting has produced great success in the past 20 years, but it also leaves unsolved reliability challenges, Liu says.
The new process does the opposite counterintuitively. “Here we demonstrate droplet manipulation that uses electrical signals to induce the liquid to dewet rather than wet, a hydrophilic conductive surface without the need for added layers,” the research team says. The millimeter-sized droplets are induced to move across the surface by an electric signal that causes the liquid to detach on one side, thus moving it. Other basic manipulations including creating, cutting, and merging of droplets can also be performed in similar ways, Liu says.
Liu says this new process removes the complexity of the system and the reliability challenges found in existing electrowetting technique, and reduces the cost of manufacturing as well. The system has been shown to handle a wide range of fluids, including common buffers and organic solvents, “promising a simple and reliable microfluid platform for a broad range of applications” that may go beyond current electrowetting applications such as liquid lenses and diagnostics kits.
The other members of the team from UCLA are professors Chang-Jin “CJ” Kim and R. Michael van Dam, and doctoral students Jia Li and Noel S. Ha.
In addition to his faculty appointment in the College of Engineering, Liu is affiliated with the Institute for Applied Life Sciences (IALS), which combines deep and interdisciplinary expertise from 29 departments on the UMass Amherst campus to translate fundamental research into innovations that benefit humankind.