In their paper, the researchers demonstrate a method for using a colloidal suspension to create crystals with the uniform structures needed for high-end technologies.
Essentially, the researchers showed that adding precisely sized chains of molecules called polymers to the colloid mixture allows them to impose order on the crystal as it forms.
"The polymers control what structures are allowed to form," said Nathan Mahynski, a graduate student in chemical and biological engineering at Princeton and the paper's lead author. "If you understand how the polymer interacts with the colloids in the mixture, you can use that to create a desired crystal."
The researchers created a computer model that simulated the formation of crystals based on principles of thermodynamics, which state that any system will settle into whatever structure requires the least energy. Panagiotopoulos's group analyzed the equilibrium state of different possible crystal shapes to understand how they were affected by the presence of different polymers.
They found that when the crystals formed, tiny amounts of polymer were trapped between the colloids as they came together. It looks like mortar in a stone wall, although the researchers say the polymer has no adhesive property. These polymer-filled spaces, called interstices, play a key role in determining the energy state of a crystal.
"Changing the polymer affects which crystal form is most stable," Mahynski said. "As the crystal forms, the polymer helps set the crystal's shape."
The polymer and the forming crystal work like a lock and key they fit together in the crystal structure with the lowest energy state. Because of this, scientists can use their knowledge of polymer physics to tailor crystal struc
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Princeton University, Engineering School