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posted by cmn32480 on Tuesday November 10 2015, @01:04PM   Printer-friendly
from the dry-underwater dept.

When a material, typically a liquid, is confined by surfaces that it doesn't like, the material can be expelled from the confining region in a process called "dewetting."

University of Pennsylvania researchers have now discovered a new facet of this "dewetting" process, showing it is easier to initiate than previously believed. Using computer modeling, they showed how variations in the density of water molecules that are confined between two hydrophobic surfaces, can speed along this process.

Better understanding of dewetting would be helpful in both controlling it and promoting it. On one hand, dewetting decreases the stability of thin films, such as the ones found in smartphone displays. On the other, dewetting is crucial to the function of the water-repelling superhydrophobic surfaces. Dewetting is also implicated in the initiation of boiling. The first places where bubbles appear in a boiling pot of water have to do with dewetting at certain surface sites.
...
Visualizing their simulations revealed a new phenomenon: In the initial stages of dewetting, stable bubbles of vapor to form near one surface, rather than span both surfaces.

"As these voids grow, it's possible for them to reach across the surface and make a tube," Patel said. "But, by that point, the vapor tube is already bigger than the critical size predicted by the previous theory and also requires less energy to form. As a result, it's easier to induce dewetting through this new pathway than by starting with a vapor tube and growing it."


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  • (Score: 2, Informative) by Gault.Drakkor on Tuesday November 10 2015, @11:08PM

    by Gault.Drakkor (1079) on Tuesday November 10 2015, @11:08PM (#261479)

    Wetting/dewetting is more obvious in something like soldering.

    Take the process known as tinning, pre-applying solder to your work pieces before soldering together. If you tried to tin with fluxless solder you can stuff copper wire into a bead of molten solder and not too much happens, pull out the wire and its still bare copper. Add some flux, and the solder is can now wet the copper wire, it sticks to the copper. The copper is now tinned/wettened with solder.

    Now lets say you sloppily soldered wire to something else, there is a big excess bead you wish to clean up. You can use a solder sucker to pull off excess. You can apply a "towel"/copper braid to soak up excess. But even after that the copper is still wet with solder. The wire is still tinned.

    If there existed a dewetting substance(anti-flux), that could be added to the bead, then solder bead would roll off leaving bare copper again. Leaving the copper 'dry' / dewetted. (As I understand the term.)

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