Bouncing liquids

Never mind hydrophobic, how about "omniphobic"?

A new material—or rather, a new shape of an existing material—has been made that rejects nearly every liquid thrown at it, both oils and waters, both acids and bases. The material is a plastic, one with slightly lower surface energy than the famous PTFE (Teflon), so it has very little stick to it to begin with.

In order to make the liquids not only not stick but actually bounce right off, they changed the shape at a microscopic level so it wasn't a smooth flat surface, but a textured surface that was mostly air:

Posted with permission from J. Am. Chem. Soc., 2013, 135 (2), pp 578–581. Copyright 2012 American Chemical Society.

Inspired by: snakes

More fantastic robots! These ones are inspired by one of the creatures I find the most fascinating: snakes.

This little guy from Carnegie Mellon Biorobotics (still tethered to its power source and remote control) can move in all kinds of ways; as the video says, not just slithering. Quite a few of these types of movement are actually very simple repetitive motions, while others are much more complicated, with more steps in the movement.

Magnetic soap

This video demonstrates a nifty advance in surfactant science: unfortunately I can't include it here, so you have to click on supporting information then the .mpg video file link to see it.

What is shown on the right, sticking to the metallic disk being lowered into the liquid, is magnetic soap. (On the left is normal, non-magnetic soap.) The little yellow blob that lifted with the magnet-on-a-stick through the clear liquid and then fell when the magnet was lifted right out of the liquid, is the soap itself.

Three different non-magnetic surfactants were made magnetic by reacting them with ferric chloride, a common industrial chemical.

A solution of ferric chloride by itself also reacts very slightly to magnets, but it finds most of its use as a coagulant, not as a soap.

Violent separation

In keeping with my original plan for this blog, I am now going to teach myself something new.

Here is something I have known about and occasionally seen since I was a kid, and know the name of, but hadn't seen it in operation and didn't actually know how it worked until I decided to write this post and figure it out:

It works exactly the same way as this thing, which I saw for the first time as an adult:

Don't plug the pressure relief valve.

The pressure relief valve is one of my favourite pieces of safety equipment.

In this case, it's just a simple valve that's designed to leak if the pressure gets above a certain point on one side. By letting a small leak happen, you avoid having the pressure get higher than the tank or pipe is designed to handle. If the pressure in a tank gets higher than it's designed to handle, you get stuff like this:

They aren't only on large industrial systems though.

That one was a little bitty (5 gallon, according to the public safety notice I found it on) hot water tank that exploded. A full size hot water tank does a lot more damage, such as done by this 80 gallon commercial hot water tank installed for a school cafeteria. Did I mention you don't ever plug the pressure relief valve? It's there for a reason.

And because it involves explosions, mythbusters naturally did a couple of episodes to find out if a hot water tank really does launch itself like a rocket and if it really can punch through the 2nd floor then the roof of a 2-story house.

So yeah, if your hot water tank has a dripping valve, don't plug it—call the repairman and put a bucket under it until then.

The reverse of a pressure relief is a vacuum relief, which lets air into tanks that you're emptying. Like this one:

Gravitational assumptions

I was working on some fluid flow at work the other day, and while trying to determine whether I could use gravity flow between a series of tanks or whether I had to put a pump in there somewhere, I wondered how a chemical plant built in microgravity would work.

Fluids or solids move because they have potential energy. (Once they're moving they also have kinetic energy.) So what kind of potential energy could, say, a pipe full of water have, if it didn't have gravitational potential and thus couldn't do any kind of gravity flow?

The first thing I thought of was pressure; this is how pumps overcome gravity and lift liquids uphill. Absent gravity, building up pressure at one end of a pipe would push the fluid toward the other, lower pressure end.

Inspired by: water striders

Here's another small robot that illustrates a fundamental property of physics. Like the Waalbot I mentioned last week demonstrated van der Waals forces, this one demonstrates surface tension.

Above is a water strider. Notice the dimples in the water where each foot touches the surface of the water.

Inspired by: geckos

This bit of news isn't actually all that new, but that's the nature of science: from discovery of physical principle to practical application takes a while.

So way back in the '70s, there was finally a microscope powerful enough to see what a gecko's hairy feet looked like. Because however they managed to climb polished glass, it wasn't glue, it wasn't suction cups, and it wasn't hooks or claws. This is what they found:

Yup, those are some hairy toes.