Inside a tiny beaker of water Harvard scientist Wim L. Noorduin has managed to coax chemicals into beautiful and delicate microscopic flowers. On a micron scale he and his colleagues have produced arrangements of crystals that resemble natural forms from roses to broad leaves… and the kicker? They self-assembled! That’s right, these aren’t just pretty pictures from an electron microscope, but a new look at how structures form chemically in nature.
“To create the flower structures,” reports the Harvard School of Engineering and Applied Sciences, “Noorduin and his colleagues dissolve barium chloride (a salt) and sodium silicate (also known as waterglass) into a beaker of water. Carbon dioxide from air naturally dissolves in the water, setting off a reaction which precipitates barium carbonate crystals. As a byproduct, it also lowers the pH of the solution immediately surrounding the crystals, which then triggers a reaction with the dissolved waterglass. This second reaction adds a layer of silica to the growing structures, uses up the acid from the solution, and allows the formation of barium carbonate crystals to continue.”
According to Noorduin, all that needs to be done is manipulate the chemical gradients in the beaker in order to control the growth behavior of the crystals and create precisely tailored structures. The influence of chemical gradients is the same thing which regulates the growth of calcium carbonate marine shells in salt water or those that signal molecules in a human embryo and initiate the plan for the body.
“For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature. This work helps to demonstrate what’s possible just through environmental, chemical changes,” says Noorduin.