Holy Jumping Water Droplets, Batman!


I think that’s where it actually started. The base. The beginning. It’s often difficult to track the history of a relationship, particularly one that starts slow and builds to an all-consuming blaze. Just when did the attraction start? Was there a moment where you knew, suddenly, wholly, “Yes, this is love”? Or was it a season of seconds, a whole swath of time in which your current infatuation incubated, ripening and growing, swelling to the point of bursting? The beginning is hard to pinpoint when seen through the lens of the present. Relationships are never tidy.

But if there was a time I could point to in my past and say, “This is where it started,” I’d have to say it was my freshman year of high school. I had this one odd period of the day that didn’t work with the rest of my second semester schedule. Due to our small school and very limited number of available classes (which was even more severely limited to my lowly freshman self), my only options were a handful of unappealing electives. A course on CAD (in retrospect, I might have enjoyed that). Band (I actually always wanted to join band, but my school was very unnaccepting of new blood- if you hadn’t been playing since you were a child, GTFO). Something else I can’t remember. And an electronics class.

I ended up in electronics. Not because I had any real interest in the subject, but because it was the lesser of all evils. Okay… and also because the boy I liked was in it.

Pathetic. I know.

Turns out, I had a real knack for electronics. Most of the course was basic wiring (with a focus on home electrical work, because this was actually a shop class), but we had to learn good ol’ Ohm’s Law and the basics of resistance, capacitance, voltage, etc.

The “love-of-my-life” spent all semester burning his name into styrofoam cups and cheating off me, but I was love-sick and stupid and possessed of almost no self-esteem. I was just happy he was paying attention to me.

…Hard to believe I wasn’t always an arrogant narcissist, right?

But, I digress. When not mooning over young Matthew, I found myself actually interested in the class. And when I went to a summer program at the University of Wyoming that year, I enrolled in a computer electronics course in order to continue tinkering with electricity. For three weeks, a boy named Kevin outlined the holes in my fishnet stockings while I took feverish notes about AND gates and resistor colors (there was a time when I had all the colors memorized), and at the end of it all, my air-headed lab partner overloaded a capacitor and blew it clean off the little board.

Two years later, my knowledge of electronics led to me teaching a section of my physics class.

I think that was it. I really do. That series of events was what broke me down, eventually opening the door to the wide world of science and culminating in the girl with the raging science hard-on you all know today.

Anyway, I tell you that because what we’re going to talk about today is vaguely related to electricity (and I felt like sharing). Turn left off of Memory Lane and pull into Science Parkway, please.

…and, unlike lying East Lansing streets, this Science Parkway will actually have some goddamn science on it.


So, some engineers over at Duke have come up with a new method of producing thermal diodes. Which could have a pretty big impact on increasing the energy efficiency of a whole slew of things.

But before we talk about any of that, we’re going to do a quick bit about diodes. As either a very basic primer or a refresher for those of you who already know a bit about electrical thingamajigs.

Diodes are interesting little devils. They only allow electrical current to travel through them one way. Current flows through one way and the diode’s all like, “Hey man, what’s up? Yeah, come on through, buddy. Gate’s open.” However, if current tries to come through the other direction, the diode goes Gandalf on its ass:

And what do these little bastards do? Well, it naturally depends on the type of diode and just how they are hooked into a circuit. Some diodes can be used to construct logic gates (like the AND gate I mentioned earlier). Some serve as a simple on/off switch controlling current. The diode you might be most familiar with lights up when current is applied in the correct direction. We call these light emitting diodes (but you can just call them LEDs). But diodes can have even more delicate applications, such as the separation of signals from radio frequencies. And some can be used to convert alternating current to direct current for power supplies. You can also use diodes to stabilize circuits, due to their fairly fixed voltage drops (but that’s a whole thing we’re not going to get into right now).

The basic principles of these electric diodes transfer over to thermal diodes. Thermal diodes can either work with electrical devices or non-electrical devices, causing heat to flow in a certain direction. So, as you might guess, they are temperature regulation devices (heat-pumps and thermoelectric coolers).

Thermal diodes can be made from solid materials, but they tend to be less effective than phase-change diodes, which transfer heat through… well, through phase changing (through condensation and vaporization). Phase-change diodes transfer heat by evaporating water from one surface and using gravity to pull the forming condensate down to a second surface. However, while phase-change diodes can transfer way more heat, they have their own severe limits. While solid-state diodes can be made into all kinds of shapes and configurations, phase-change diodes are at the mercy of gravitational limits and one-dimensionality.

No planar phase-changing for you.

But that’s where our Duke folks step in. What they did was use a hydrophobic… oh, excuse me, a superhydrophobic material, which causes water droplets to literally propel themselves off of it. Opposite this superhydrophobic material (which, in case you were curious, was created using electroless galvanic deposition of silver nanoparticles onto a copper substrate, which was then coated in a layer of 1-hexadecanethiol) they set up a superhydrophilic (i.e. it really loves it some water) material (basically made with copper oxidized by oxygen plasma… I just love the phrase “oxygen plasma”). So, heat comes in from one direction. It evaporates the water, causing condensation which hits the superhydrophobic plate. The water leaps the fuck off the plate and is embraced in the welcoming bosom of the superhydrophilic plate. And, because of the nature of the plates, it can only work in one direction (so, if the superhydrophilic plate is warmer than the superhydrophobic plate, heat transfer can’t happen).

Boom. Diode.

What’s great about this is that it allows for a lot more flexibility in application, both because of the new versatility of shape and configuration, as well as the fact that it doesn’t rely on gravity no mo’ (the water droplets here are microscopic in size, so gravity has a negligible effect on the whole thing). Which is good, because you know what they say about gravity. And what makes all this so awesome is that it opens the door for phase-change thermal diodes to be used in all kinds of things, from computer chips to large solar panels.

It’s a big win for energy efficiency, that’s for sure. Certainly worth a nod from me.

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