When we think of crystals, most of us probably either picture spiky things like snowflakes, or cube-shaped objects like grains of sugar. Researchers from the Harvard School of Engineering and Applied Sciences, however, have recently coaxed barium carbonate crystals to grow into very miniature replicas of soft, curved flowers.
Crystals in general will grow in response to changes in the chemical gradient within a solution. If there’s more of one particular compound present in a certain area of the liquid, for instance, the resulting change in pH may cause crystals to precipitate either towards that area or away from it.
By painstakingly manipulating that chemical gradient within a beaker of fluid, a team of scientists led by Prof. Joanna Aizenberg were able to grow a number of different crystalline “flowers” on the surface of glass slides, metal blades and even a penny – each flower being mere microns in size.
More precisely, the team dissolved barium chloride salt and sodium silicate in water. When carbon dioxide from the air also naturally dissolved in the water, it set off a reaction that caused barium carbonate crystals to form. This caused the pH of the water surrounding the crystals to get lower, which in turn caused the dissolved sodium silicate to form into a layer of silica on them, thus extending their growth process.
“The precipitation happens spontaneously, but if you want to change something then you can just manipulate the conditions of the reaction and sculpt the forms while they're growing,” said postdoctoral fellow Wim L. Noorduin, lead author of a paper on the research, that was recently published in the journal Science. For example, “broad-leafed” structures can be created by increasing the concentration of carbon dioxide, while ruffled structures can be made by reversing the pH gradient at just the right moment.
While the tiny flowers are indeed pretty to look at, the research could have big implications in fields such as optics and electronics. “Our approach is to study biological systems, to think what they can do that we can’t, and then to use these approaches to optimize existing technologies or create new ones,” said Aizenberg. “Our vision really is to build as organisms do.”
Source: Harvard University
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