Atomic scale imaging reveals an easy path for crystal formation

Aluminum hydroxide, represented here in orange, undergoes fluctuations between structures before forming an ordered crystal. Credit: Nathan Johnson | Pacific Northwest National Laboratory

What do clouds, televisions, pharmaceuticals and even dirt under our feet have in common? Everyone has or uses crystals in some way. Crystals are more than just precious stones. Clouds form when water vapor condenses into ice crystals in the atmosphere. Liquid crystal displays are used in a variety of electronics, from televisions to instrument clusters. Crystallization is an important step in drug discovery and purification. Crystals also make up rocks and other minerals. Their crucial role in the environment is at the heart of material science and health science research.

Scientists have yet to fully understand how crystallization occurs, but the importance of surfaces in promoting the process has long been recognized. Research from the Pacific Northwest National Laboratory (PNNL), the University of Washington (UW) and Durham University sheds new light on how crystals form on surfaces. Their findings were published in Science advances.

Previous studies on crystallization have led scientists to form the classical nucleation theory, the predominant explanation of why crystals begin to form or to nuclearsi. When the crystals nucleat, they start out as small ephemeral clusters of a few atoms. Their small size makes the clusters extremely difficult to detect. Scientists managed to collect only a few images of such processes.

“New technologies are making it possible to visualize the crystallization process like never before,” said chemist from PNNL’s division of physical sciences Ben Legg. He partnered with PNNL Battelle Fellow and UW Affiliate Professor James De Yoreo to do just that. With the help of Professor Kislon Voitchovsky of the University of Durham in England, they used a technique called atomic force microscopy to observe the nucleation of an aluminum hydroxide mineral on a mica surface in water.

Mica is a common mineral, found in everything from drywall to cosmetics. It often provides a surface for the nucleation and growth of other minerals. For this study, however, its most important feature was its extremely flat surface, which allowed the researchers to detect clusters of a few atoms as they formed on the mica.

What Legg and De Yoreo observed was a crystallization model that was not foreseen by classical theory. Instead of a rare event in which a cluster of atoms reaches a critical size and then grows to the surface, they saw thousands of floating clusters that have merged into an unexpected pattern with gaps persisting between the crystalline “islands”.

After careful analysis of the results, the researchers concluded that while some aspects of the current theory were true, their system eventually followed a non-classical path. They attribute it to the electrostatic forces of the charges on the surface of the mica. As many types of materials form charged surfaces in water, the researchers speculate that they have observed a widespread phenomenon and are excited to look for other systems where this non-classical process could occur.

“The hypotheses of classical nucleation theory have far-reaching implications in disciplines ranging from materials science to climate prediction,” said De Yoreo. “The results of our experiments can help produce more accurate simulations of such systems.”

Raise the Order: A new study reveals the importance of liquid structural ordering in crystallization

More information:
Benjamin A. Legg et al, Hydroxide films on mica form charge-stabilized microphases that bypass nucleation barriers, Science advances (2022). DOI: 10.1126 / sciaadv.abn7087

Provided by Pacific Northwest National Laboratory

Citation: Atomic Scale Imaging Reveals Easy Path for Crystal Formation (2022, September 23) Retrieved September 23, 2022 from easy-route. html

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