Self-Healing Material: Proof is in the Mayonnaise

Microscopic view of an emulsion.

A perfect crystal is a beautiful thing. The atoms inside the crystalline matrix align with zero flaws, zero atoms out of place, zero extra space. But with all of these zeros come a lot of gains. Crystals tend to be stronger than randomly ordered substances. They also tend to transmit electricity better.

The problem is, of course, obtaining that perfection.

However, new research from the University of Chicago shows that if done properly, some materials will organize themselves into perfect crystals. What’s more, if a defect is introduced, the substance will “heal” it all on its own.

The substance in question in the experiment is a form of “soft matter.” Think mayonnaise, or any oil and water based salad dressing. The oil and water components don’t want to mix. But thanks to surfactants – a stabilizer that is equally happy in both oil and water – found within the egg yolks, you can achieve a balance.

Though mayonnaise may look like a perfectly homogeneous concoction, it only looks that way to the naked eye. If you zoomed in more closely, you’d see that it is in fact a collection of tiny oil droplets kept a perfect distance away from each other with the help of the surfactants.

In the recent experiment, the roles of the droplets and surfactants were played by glycerol droplets and acrylic glass particles emulsified in oil. When put into a spherical shape, the droplets aligned themselves into a perfect crystal along the surface, thanks to the particles’ positive electric charge that repelled them from each other.

Then the scientists introduced a disturbance. Using optical tweezers – beams of laser light capable of moving tiny particles (I know! Awesome, right?!) – they put a single droplet on the surface of the sphere. The nearby particles shifted slightly, which in turn caused a chain reaction throughout the sphere. But rather than introducing chaos, the perturbation made its way in opposite directions until the molecular structure reached a new perfect crystalline structure.

By comparison, if the same thing were to be done on a flat surface, the nearby particles would rearrange themselves, but it wouldn’t spread out much further than that. You’d have an imperfect structure localized to the immediate vicinity of the perturbation.

The researchers on the project – William Irvine, assistant professor in physics at the University of Chicago, and Paul Chaikin of New York University – believe the results could be used to increase the conductivity of certain materials. For example, it might be possible to flex a piece of graphene into a more spherical shape in order to reduce the number of defects and improve its mechanical characteristics.

That, in turn, could lead to all sorts of advances in the materials world. Graphene is made of carbon sheets just one atom thick and could be used in future high frequency transistors, display screens in mobile devices and storing hydrogen for fuel cell powered cars.

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About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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