Water Droplet Images Captured With High-speed Camera May Lead to New Technological Breakthroughs

Water droplets may seem ordinary to the naked eye, but when imaged with a high-speed, high-resolution camera, the tiny droplets take on surprising shapes, and the study of the droplets' behavior may lead to new applications in everything from inkjet printing to microfluidics.

Researchers at Cornell University have published a high-resolution "photo album" of more than 30 shapes an oscillated drop of water can take as its passed through a square of mesh with holes 50-microns across.

"What is really special about this study is the high-quality imaging we were able to capture of these oscillating droplets," said Susan Daniel and assistant professor of chemical and biomolecular engineering and lead study author. "We created an imaging platform where we could look at the drop from the top, to enable us to see the characteristic shapes better than anyone has before."

With the aptly named "Omniview" imaging platform, water can be photographed at multiples angels by shining a light through the mesh's holes; the deflection of the drop's surface refracts the light, which is seen as a deformation of the mesh and captured by the high speed camera.

The researchers also observed the effects of oscillating the water drops at various frequencies and found that certain frequencies correspond to the shape of a drop of a specific size, not unlike certain frequencies corresponding to a given length on a musical instrument's string.

Another observation was that some of the droplets take on multiple shapes when vibrated with a single driving frequency, which can be likened to physicists observing two different energy states simultaneously in an excited molecule.

"Without the high-speed imaging, we wouldn't have been able to see the drops exhibiting these kinds of mixed behaviors," Daniel said.

Applications for the finding are numerous and should provide insight into further studies, Daniel said. NASA, for example, is interested in understanding how water droplets move on surfaces in low gravity. And in high-resolution printing, the spread of a droplet as it hit a surface will determine image resolution, and a further study of the effects on how the droplets are hitting the printing surface could have profound effects on the technology, according to Daniel.

Daniel and her colleagues' work will be published this week in the journal Physical Review E.

The full study, images and animations can be downloaded here:  https://cornell.box.com/droplets