Miniscule, delicate and blossoming nanostructures: these colorized SEM images show how microscopic flowers unfurl as a result of a chemical reaction – and they can only be observed under a scanning electron microscope.
Every single structure of these tiny artworks is no thicker than a human hair: Wim L. Noorduin, a former postdoc at the Harvard School of Engineering and Applied Sciences, and Prof. Joanna Aizenberg, have discovered a way to control the speed at which crystals grow in order to precisely determine the way in which these crystals self-organize.
This means they can create tailored structures simply by modifying the chemical parameters. Just by altering the temperature, the pH and the carbon dioxide from the air, they were able to coax the nanostructures into the desired shape. The scientists believe their results clearly demonstrate the possibilities afforded by nanostructures when users get the self-organization process to work for them. If they can be produced artificially and in a customized way, this could enhance – or even completely redefine – a whole host of technologies, from catalysis and optics through to statics.
“For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature,” says Wim L. Noorduin. “This work helps demonstrate what’s possible just through environmental and chemical modifications.”
Enhancing existing technologies
The crystals grow on glass slides and metal blades. This approach can be used to optimize existing technologies, or to create new ones. Chemical variables frequently influence growth in nature: calcium carbonate forms curved marine shells underwater, and the characteristics of signaling molecules in a human embryo help shape the blueprint for the body.
“When you look through the electron microscope, it really feels a bit like you’re diving in the ocean. Sometimes I even forget to capture images because it’s so nice to explore.”
How does it work?
Noorduin and his colleagues created the flower structures by dissolving barium chloride and sodium silicate (or “waterglass”) into a beaker of water. Carbon dioxide naturally dissolves in the water, setting off a reaction which precipitates the formation of barium carbonate crystals. It also lowers the pH of the solution immediately surrounding the crystals, which then triggers a reaction with the dissolved waterglass and adds a layer of silica to the growing structures. Then it uses up acid from the solution and allows the barium crystals to continue growing.
Since 2015 Wim L. Noorduin is heading the Self-Organizing Matter group, which focuses on fundamental questions regarding the creation and design of structured materials with novel functionalities. In particular, the group aims to design physical-chemical schemes to self-organize microscale devices and functional molecules.