Tait S. Pottebaum, assistant professor in the Department of Aerospace and Mechanical Engineering at the USC Viterbi School of Engineering, has been awarded a Faculty Early Career Development grant from the National Science Foundation for his work in fluid dynamics.

The $400,336 award will support Pottebaum’s work to produce a new measurement technique and apply it to flows that must be understood in order to enable the development of new microfluidic devices.

The five-year award, which becomes effective May 1, is among the highest honors given to young faculty. The awards are highly competitive and support individual early career efforts to advance research and education in the recipient’s discipline.

Pottebaum’s research focuses on tiny microfluidic devices that are controlled by temperature. Examples of these devices include pumps that move bubbles or droplets in micro-channels and free surface flows that move on micro-patterned surfaces.

These types of pumps are becoming increasingly common, with applications ranging from “lab-on-a-chip” devices for DNA replication and bio-hazard detection, microelectromechanical system (MEMS) switches and inkjet printer nozzles.

“While the velocity fields at these moving interfaces have been previously measured, the temperature gradients that drive the flows have not because a suitable technique doesn’t currently exist,” said Pottebaum, whose award will support research to measure the thermal gradients at moving interfaces between liquids and air in these devices.

“By simultaneously measuring the velocity field at the interface, the accelerations and forces produced by the thermal gradients can also be determined, allowing us to develop and experimentally test models of thermocapillary actuation,” he explained.

To accomplish this, a new optical, whole-field temperature measurement technique for microfluidic devices will be developed using encapsulated thermochromic liquid crystal thermometry, which previously has been used only at the macro-scale.

“This technique will be applied to three representative flows: a contact line on a surface that is open to the air; an isolated bubble in a water-filled capillary tube; and an isolated droplet in a capillary tube. In all three cases, a temperature gradient will be applied across the setup to drive the motion,” Pottebaum said.

But there are many challenges to using this technique at the micro-scale, he said, including the constraints that are placed on imaging and illumination, in particular the proximity of the measurements to curved interfaces and to surfaces from which light will scatter.

“To overcome this challenge, I will apply circular polarization filtering,” Pottebaum said.

By improving the understanding of the forces that act on liquid-air interfaces, Pottebaum’s research will enable the invention and refinement of new microfluidic devices, such as medical testing devices, electronics cooling systems, and sensors for hazardous substances.

The work also will aid future research by allowing researchers to use the new measurement technique in all types of micro-scale flows that are driven by temperature gradients.

In congratulating Pottebaum on his award, Michael Kassner, chair of the USC Viterbi School Aerospace and Mechanical Engineering Department, called the research a significant step in the development of next-generation fluidic devices.

“We are very proud of Tait,” he said. “This is the second year in a row that one of the aerospace and engineering department’s assistant professors has received a CAREER award. We look forward to our third next year.”

Pottebaum earned his bachelor of science degree in aerospace engineering from USC. He subsequently earned his master’s degree and Ph.D. degree in aeronautics from the California Institute of Technology in 1999 and 2003, respectively, and pursued additional studies in planetary science.

As a postdoctoral scholar in aeronautics at Caltech, he performed experiments on the flow inside telescope enclosures. His research interests include micro-scale convective heat transfer, bluff-body aerodynamics, buoyancy-driven flows, fluid-structure interactions, and non-invasive temperature and velocity measurement techniques.