Physical Ecology Lab

A water droplet immersed in a mixture of anise oil and ethanol displays some pretty complicated dynamics. Its behavior is driven, in part, by the variable miscibility of the three liquids. Water and ethanol are fully miscible, anise oil and ethanol are only partially miscible, and anise oil and water are completely immiscible. These varying levels of miscibility set up a lot of variations in surface tension along and around the droplet, which drives its stretching and eventual jump.

Once detached, the droplet takes on a flattened, lens-like shape that continues to spread. That spreading is driven by the mixing of ethanol and water, which generates heat and, thus, convection around the drop. This not only spreads the droplet, it causes turbulent behavior along the drop’s interface. (Image and video credit: S. Yamanidouzisorkhabi et al.)

When glaciers form, they do so in layers, with clear blue ice sandwiched between sediment and air-bubble-filled white ice. Because each of these layers absorbs sunlight differently, they don’t melt evenly. The spikes and ridges seen in this ice formed because of this differential melting between layers. The blue ice is particularly good at absorbing visible wavelengths of light, and so erodes more easily than the other layers.

Although the results look somewhat similar to the penitente ice seen at high altitudes, the formation mechanisms are a little different. Penitentes rely heavily on sublimation — where their ice and snow change directly into a gas — rather than the melting seen here. That said, both eroded forms depend strongly on how different layers within them absorb and scatter sunlight. (Image credit: J. Van Gundy; via EPOD; submitted by Kam-Yung Soh)

Although we typically describe hydrophobic surfaces as “water-repelling,” we could just as easily focus on the fact that they’re “air-attracting.” This video from The Action Lab demonstrates that property nicely with a hydrophobic-coated “boat” that’s effectively unsinkable, thanks to its ability to trap air pockets.

Even punching holes through the boat doesn’t sink it because its surface is so chemically and physically attractive to air that the bubble won’t budge. In fact, as the video demonstrates, the only effective way to remove the hydrophobicity is to remove the air bubble by using a vacuum chamber. But even then, the effect only lasts until air is reintroduced to the boat. (Image and video credit: The Action Lab)

P.S. – No, this is not an April Fool’s joke, just actual science! – Nicole

In medicine, many medications contain molecules too large to be easily absorbed through the intestinal wall, so these so-called biologics — like the insulin administered to diabetics — are injected into the body. Researchers are studying ways that such injections could eventually be replaced with pills, but there are plenty of challenges involved.

Some substances, known as transient permeability enhancers, allow the intestines to absorb larger molecules, but they work for only tens of minutes, which means researchers must understand how and when to administer them relative to the medication they help patients absorb. To do so, researchers are building computational fluid dynamics models of the human digestive system so that they can better understand how and when different kinds of pills break down in the body. (Image credit: Macro Room, source; via CU Engineering; submitted by Jenny B.)