Flickering droplets in space confirm late professor's theory

At a time when astronomers around the world are reveling in new views of the distant cosmos, an experiment on the International Space Station has given Cornell researchers new insight into something a little closer to home: water.

Additionally precisely, the space station’s microgravity environment illuminated how water droplets oscillate and propagate on solid surfaces – knowledge that could have very earthly applications in 3D printing, spray cooling, and manufacturing and coating operations.

The team’s paper, “Oscillations of Drops with Cellular Make contact with Lines on the Intercontinental Place Station: Elucidation of Terrestrial Inertial Droplet Spreading”, was published on 16 August in Actual physical Review Letters. The lead author is Joshua McCraney, MS’ 19, Ph.D.’ 20.

The experiment and its results, while successful, are also bittersweet. The paper’s co-lead author, Paul Steen, Maxwell M. Upson Professor at the Smith School of Chemical and Biomolecular Engineering at the Higher Education of Engineering, died in September 2020 , just before the experiment was carried out.

“It is sad that Paul could not see the experiments launch into space”, said the co- lead author Susan Daniel, Fred H. Rhodes Professor at Smith University of Chemical and Biomolecular Engineering and longtime Steen collaborator. “We hope we did well in the end, and that the paper we produced from the work will make him proud.”

Daniel started collaborating with Steen shortly after arriving at Cornell as an assistant professor in 2007. While his current research focuses on the biological interface of the coronavirus, his postgraduate work focused on chemical interfaces and fluid mechanics – an area in which Steen made a number of theoretical predictions based on how droplets resonate when subjected to vibrations. The two researchers immediately connected.

“He knew the theory and made predictions, and I knew how to run the experiments to test them,” Daniel said. “Basically, from the time I arrived here in 2007 until he passed away, we worked to try to understand how liquids and surfaces interact with each other. others, and how the get hold of line at the interface between them behaves in different situations.

Steen then developed this project by cataloging the energy states of droplets as evidenced by these resonant shapes, organizing them into a “periodic table” classification.

In 2016, Steen and Daniel received a four-year grant from the Countrywide Science Foundation (NSF) and NASA’s Center for the Development of Science in Area to conduct fluid dynamics research aboard the US National Laboratory of the International Space Station.

Space is an ideal place to study fluid behavior due to the drastic reduction of gravity, which on the ISS is about one millionth of its Earth level. This means that fluid-area interactions that are so small and fast on Earth that they are practically invisible can be, in space, near 10 times larger – from microns to centimeters – and their duration slows down by almost 21 times.

“It’s harder to study these falling motions, experimentally and fundamentally, when you have gravity in your way,” Daniel said.

emphasizing on how a drop of water’s contact line – or outer edge – slides back and forth over an area, leading the liquid to spread, a phenomenon that can be controlled by varying the vibrational frequencies.

The team has prepared meticulous directions for the astronauts, compressing four years of planning into a multi-minute experience in which every second was thin itement choreographed.

As researchers monitored and provided real-time information on the ground, the astronauts deposited water droplets of 10 ml by using a syringe on nine different hydrophobic surfaces with varying degrees of roughness. They also forced pairs of droplets to merge and placed droplets on an oscillator and tuned its vibrations to achieve the targeted resonance shapes. The oscillating and agitating motions of the water droplets were filmed, and the researchers spent the next year analyzing the data.

This analysis ultimately confirmed the Steen’s theories on how the density and surface stress of a liquid control the mobility of the speak to line, overcoming the roughness of a floor.

Daniel credits co-author Joshua Bostwick, Ph.D.’ 10, a former Steen student and now Stanzione Collaboration Associate Professor at the Clemson University, to ensure that the results of the experiment match Steen’s theoretical predictions.

“Josh was able to continue the theoretical aspect of this work in the absence of Paul, which I was not prepared to do. It was nice to have him join the team and help us make sure we could extract everything we could from the data we collected,” Daniel said. “Now we can basically use the theory that Paul created to make predictions, for example, in processes where you spray droplets on surfaces, or in 3D printing, or when liquids spread very quickly over a floor.”

Vanessa Kern, Ph.D.’ 20, was also a co-author of the ‘article.

The research was supported by the NSF and NASA’s Center for the Development of Science in Place.

Related Articles

Back to top button