Mad About Science: Aerogel and oobleck

By Zach Hagadone
Reader Staff

Human beings are generally unsettled when things don’t act quite like they’re supposed to. This, of course, is a prehistoric trait rooted in defense — our brains naturally seek out patterns on which to base our understanding of the world around us, and when those patterns fail to repeat in a way that makes sense, we start to wonder if there might be a threat afoot.

As Smithsonian Magazine put it in a 2015 article, “[W]hen you’re creeped out, your brain and your body are telling you that something is not quite right and you’d better pay attention because it might hurt you.”

Following that, there’s something slightly unsettling about substances like aerogel and oobleck — the former a porous, low-density gel with the properties of a strong, heat-resistant solid; the latter, a putty-like material that acts like a liquid until you put it under pressure and it becomes a solid. Relieve the stress applied to oobleck, and it will return to its aqueous state.

Neither material really makes sense on first inspection, but once you learn more about them, any lingering creeps turn to fascination. 

Aerogel looks and feels like nothing so much as condensed steam or smoke. Or, as it was described in a 2019 video featuring celebrity astrophysicist Neil deGrasse Tyson and Adam Savage, of popular TV series MythBusters, “it looks like a ghost.”

In a more scientific vein, NASA uses aerogel for a variety of applications — including insulation — and has pioneered processes for making the material even stronger and more flexible. According to a NASA web page devoted entirely to the substance, aerogel is created primarily using silica mixed with a solvent to produce a gel. Liquid carbon dioxide is then diffused into the gel, where it moves past its “super critical point,” wavering between a liquid and a gas. Then it undergoes several rounds of venting until all traces of liquids are gone from the gel, leaving “nano pores” that are so small they’re invisible to the human eye. Despite that, silica aerogel is about 95% porous.

“The pores are so small, and gas phase heat conduction is very poor,” according to Mary Ann Meador, a chemical engineer who leads the aerogel team at NASA’s Glenn Research Center. “Molecules of air cannot travel through the aerogel, so there is poor heat transfer through the material.”

The insulating properties of aerogel have earned it applications such as on the Mars Rover and, when created using polymers, can be made super-strong, more flexible and yet still between 85-95% porous, retaining the insulating qualities of silica-based aerogel without the brittleness. That polymer base also makes the material “ideally suited for use in a vacuum, like in space, as well as in different gravity scenarios, such as the moon or other planets,” according to NASA.

Oobleck, on the other hand, is what’s described as a “non-Newtonian fluid,” meaning it doesn’t abide by Sir Isaac Newton’s “law of viscosity,” which basically says that when pressure or stress is applied to a fluid, that pressure or stress is applied equally throughout the layers of the fluid. For example, water will shoot out of a hose at a rate proportional to the amount of pressure put on it at the spigot, meanwhile maintaining its viscosity. With non-Newtonian fluids, the viscosity changes with stress. Some become more liquidy, while others — like oobleck — take on solid characteristics.

Named after the bizarre, gooey substance of the same name in the 1949 book Bartholomew and the Oobleck, by Dr. Seuss, oobleck is one of the most entertaining and accessible ways to explore non-Newtonian fluids. 

All you need to make oobleck is one or two cups of cornstarch, a cup of water and a mixing bowl (food coloring optional, for greater effect). Pour a cup of cornstarch into the bowl, then slowly mix in the water — stirring until the substance starts to harden when tapped. Add cornstarch and/or water, depending on whether it’s getting too liquified or too thick.

Oobleck works similarly to quicksand: the super-fine cornstarch particles mixed with water move together when put under pressure, but dip your hand slowly into the mixture, and your fingers will move through the substance easily.

It’s a cheap and easy science experiment perfect for the kitchen counter, non-toxic and perfectly safe for kids. They’ll have to save up for the aerogel, however. Even a small piece of the hyper-lightweight material can cost upwards of $50. Some sources put the price of a pound at about $23,000 — slightly more than a comparable quantity of gold.

Stay curious 7B!