Cambridge, MA - Scientists have long studied how atoms and molecules structure themselves into intricate clusters. Unlocking the design secrets of Nature offers lessons in engineering artificial systems that could self-assemble into any desired form.
In the January 29th issue of Science, a team from Harvard led by Vinothan Manoharan and Michael Brenner, presents additional clues to how and why groups of atoms and molecules may favor less symmetrical and more complex, flexible geometric patterns.
The answer relates to a familiar concept in physicsentropy. The researchers literally first caught sight of the link by using magnetic "stick and ball" construction toys.
Manoharan, Associate Professor of Chemical Engineering and Physics in Harvard's School of Engineering and Applied Science (SEAS) and Department of Physics, and his colleagues used colloidal particles, a suspended chemical mixture seen in semi-solid foods like mayonnaise, to simulate the clustering behavior of atoms and molecules.
"To allow clusters to form, we put a few tiny polystyrene spheres in microscopic cylindrical wells filled with water. The particles act as 'sticky' hard spheres and naturally cluster together just like groups of nearby interacting atoms and molecules do," says Manoharan.
The researchers expected that simple, highly symmetric shapes would arise most often. Instead, two surprising, related, and scalable phenomena arose when the number of particles used in their experiments reached six or rose above nine.
Six particles can form into a symmetrical octahedron and into a more complex tri-tetrahedron shape. In terms of chemical structure, each shape results in 12 bonds, and hence, has the same amount of potential energy.
With the potential energy being equal, Manoharan and colleagues thought that both shapes would occur in equal proportion. They found, however, that the tri-tetrahedron occurs 20 times more of
|Contact: Michael Patrick Rutter|