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Credit: Miskin and Jaeger; PNAS.
Wait for it, wait for it, wait for it … I realize this brief video doesn’t appear to be doing anything for the first few seconds, but once it gets going, it is hypnotic and revealing about how dense suspensions can behave.
This video was made by Heinrich Jaeger, the William J. Friedman and Alicia Townsend Friedman Professor in Physics, at the University of Chicago, along with graduate student Mark Miskin.
According to a news release from the university, Miskin and Jaeger thought that when they forced a suspension composed of water containing zirconium dioxide particles measuring 850 microns in diameter through a nozzle, it would “behave strictly like viscous liquids, which tend to flow less freely than non-viscous liquids.”
As can be seen in the video, most of the time it does behave like a viscous liquid, except for a moment when the neck stretches, reaching an extreme point. “While the liquid deforms and becomes thinner and thinner at a certain spot, the particles also have to move with that liquid. They are trapped inside the liquid,” Jaeger explains in the release. “The particles in a dense suspension conspire to interact with the liquid in a way that, when it’s all said and done, a neck forms that shows signs of a split personality: It thins in a non-viscous fashion, like water, all the while exhibiting a shape more resembling that of its viscous cousins.”
I don’t know the intricacies of these topics, but apparently this is a controversial topic. “It is a somewhat heretical view that this viscosity should not matter,” Jaeger says. “Who would have thought that?”
According to the release, Miskin and Jaeger’s study “showed that particles cause deformations and often protrude through the liquid, rendering any such description incomplete until fundamental questions about the interface between a liquid mixture and its surroundings are properly addressed.”
The duo also have developed a mathematical model that can evaluate different viscosities, particle sizes and suspending liquids and then predict how the droplet necks evolve over time until they break apart.
Miskin and Jaeger work is featured in a PNAS paper “Droplet Formation and Scaling in Dense Suspensions” (doi:10.1073/pnas.1111060109).
They also have two other droplet videos available here and here.
We told you earlier about a pitch drop experiment in Australia, which generates one drop per decade or so. Perhaps the UC experiment explains some of the physics involved there, too.