Academic journal article The Science Teacher

Beautiful "Nano Flowers" Self-Assemble in a Beaker

Academic journal article The Science Teacher

Beautiful "Nano Flowers" Self-Assemble in a Beaker

Article excerpt

Delicate crystal flower structures--measured not in inches but in microns--have been formed in a Harvard laboratory. These minuscule crystals, curved and delicate, don't resemble the cubic or jagged forms normally associated with crystals, though that's what they are. Rather, fields of carnations and marigolds seem to bloom from the surface of a submerged glass slide, assembling themselves a molecule at a time.

By simply manipulating chemical gradients in a beaker of fluid, Wim L. Noorduin, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS) and lead author of a paper appearing in Science, has found that he can control the growth behavior of these crystals to create precisely tailored structures.

"For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature," Noorduin said. "This work helps to demonstrate what's possible just through environmental, chemical changes."

The precipitation of the crystals depends on a reaction of compounds diffusing through a liquid solution. The crystals grow toward or away from certain chemical gradients as the pH of the reaction shifts back and forth. The conditions of the reaction dictate whether the structure resembles broad, radiating leaves, a thin stem, or a rosette of petals.

It is not unusual for chemical gradients to influence growth in nature; for example, delicately curved marine shells form from calcium carbonate under water, and gradients of signaling molecules in a human embryo help set up the plan for the body. …

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