Self-Stacking Nanogrids

Estimated reading time: 4 minutes

Polymers are long molecules made from basic molecular units strung into chains. Plastics are polymers, and so are biological molecules like DNA and proteins. A copolymer is a polymer made by joining two different polymers.

In a block copolymer, the constituent polymers are chosen so that they’re chemically incompatible with each other. It’s their attempts to push away from each other — both within a single polymer chain and within a polymer film — that causes them to self-organize.

In the MIT researchers’ case, one of the constituent polymers is carbon-based, the other silicon-based. In their efforts to escape the carbon-based polymer, the silicon-based polymers fold in on themselves, forming cylinders with loops of silicon-based polymer on the inside and the other polymer bristling on the outside. When the cylinders are exposed to an oxygen plasma, the carbon-based polymer burns away and the silicon oxidizes, leaving glass-like cylinders attached to a base.

To assemble a second layer of cylinders, the researchers simply repeat the process, albeit using copolymers with slightly different chain lengths. The cylinders in the new layer naturally orient themselves perpendicularly to those in the first.

Chemically treating the surface on which the first group of cylinders are formed will cause them to line up in parallel rows. In that case, the second layer of cylinders will also form parallel rows, perpendicular to those in the first.

But if the cylinders in the bottom layer are allowed to form haphazardly, snaking out into elaborate, looping patterns, the cylinders in the second layer will maintain their relative orientation, creating their own elaborate, but perpendicular, patterns.

The orderly mesh structure is the one that has the most obvious applications, but the disorderly one is perhaps the more impressive technical feat. “That’s the one the materials scientists are excited about,” Nicaise says.

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