An experiment on the International Space Station has given Cornell researchers a new perspective on water, at a time when astronomy around the world is celebrating new views of the distant universe.
The space station's microgravity environment illuminated the ways in which water droplets spread across solid surfaces, which could have very earthbound applications in manufacturing and coating operations.
The paper "Oscillations of Drops with Mobile Contact lines on the International Space Station: Elucidation of Terrestrial Inertial Droplet Spreading" was published in August. He is the lead author.
The experiment and its results are a mixed bag. The paper's co-senior author died just before the experiment was to be done.
Susan Daniel is the Fred H. Rhodes Professor in the Smith School of Chemical and Biomolecular Engineering. We hope that the paper that we produced from the work would make him proud.
After she first arrived at Cornell as an assistant professor, Daniel began working with her. While her current research is focused on the biological interface of the coronaviruses, her graduate work was in chemical interface and fluid mechanics. The two researchers were able to communicate.
Daniel said that he knew how to execute the experiments and that he knew how to make predictions. We worked on understanding how liquids and surfaces interact with each other and how the contact line at the interface between them behaves under different conditions after he passed away.
A photo album of dozens of possible shapes was created by their collaboration. As a result of those shapes, the droplets' energy states were categorized into a "periodic table".
The National Science Foundation and NASA's Center for the advancement of Science in Space awarded a four-year grant to Daniel and Steen in 2016 to conduct fluid dynamics research in space.
The International Space Station is a good place to study fluids because of the reduction of gravity. In space, fluid-surface interactions which are so small-scale and swift on Earth that they are practically invisible can be ten times larger, and their duration is 30 times longer.
When you have gravity in your way, it's hard to study drop motions.
A few resonance shapes from their photo album that they wanted to explore in detail, with a focus on how a water droplet's contact line slides back and forth across a surface, a phenomenon that can be
Four years of planning was cut short by the team's preparation of instructions for the astronauts to follow.
The researchers monitored and provided feedback in real time on the ground as the astronauts deposited 10 mL water droplets onto nine different hydrophobic surfaces. They forced pairs of droplets to coalesce together and placed droplets on an oscillator to get the targeted resonance shapes. The researchers spent a year analyzing the data after filming the water droplets' wobbling and moving.
The analysis confirmed that a liquid's density and surface tension control the contact line's mobility.
Daniel credits the co-author with ensuring that the experiment results were in line with the theory.
In Paul's absence, Josh was able to carry on with the theoretical part of the work, which was not something I was prepared to do. Daniel said it was nice to have him back and help make sure we were able to get everything we needed from the data we collected. We can use the theory that Paul created to make predictions, for example, in processes where you're spraying droplets on surfaces, or in 3D-printing, or where liquids spread across a surface really quickly.
The paper was co-authored byVanessa Kern and others.
More information: J. McCraney et al, Oscillations of Drops with Mobile Contact Lines on the International Space Station: Elucidation of Terrestrial Inertial Droplet Spreading, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.084501 Journal information: Physical Review Letters
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