'Electrospray' droplet research yields surprising, practic...( WEST LAFAYETTE Ind. - Chemical engin...)

WEST LAFAYETTE, Ind. - Chemical engineers at Purdue University are the first to mathematically describe precisely how droplets form when liquids are exposed to electric fields, an advance that could have applications in areas ranging from manufacturing to medical diagnostics.

The technique of using small droplets created by subjecting liquids to electric fields is vital for a variety of applications, from a type of industrial painting called electrospraying, to a method for analyzing molecules in analytical chemistry, to manufacturing tiny micro- and nanoparticles for research and industry.

"Despite its importance, industry doesn't really understand exactly how the drops form," said Osman Basaran, the Reilly Professor of Fluid Mechanics in Purdue's School of Chemical Engineering.

New findings showed that a liquid's viscosity plays a vital role in drop formation and size, a discovery that contradicts conventional wisdom, Basaran said.

The researchers first created simulations to describe droplet formation mathematically, and then they performed experiments to support the computational work.

"Computational simulations are now making it possible to understand such phenomena," he said. "But you always want to back up simulations with experimental data if at all possible."

The findings are detailed in a paper appearing in the January issue of Nature Physics. The paper was written by doctoral student Robert T. Collins, undergraduate student Jeremy J. Jones, professor Michael T. Harris, and Basaran, all in the School of Chemical Engineering.

Researchers have known for decades that applying an electric field to liquid drops causes the formation of structures that have a perfect cone at the leading edge.

"Each drop takes on the shape of a chocolate kiss," Basaran said.

Then, a thin ribbonlike strand of fluid is emitted from the leading edge of the droplet and breaks up into smaller drople
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