A new theory has been proposed for building nanoscale structures that could have radical implications for industry and our understanding of life.
Salvatore Torquato of Princeton University and colleagues have published a paper in Physical Review Letters outlining a mathematical approach to creating desired configurations of nanoparticles by manipulating how the particles interact.
The authors devised “an inverse statistical-mechanical methodology to find optimized interaction potentials that lead spontaneously to a target many-particle configuration. Target structures can possess varying degrees of disorder, thus extending the traditional idea of self-assembly to incorporate both amorphous and crystalline structures as well as quasicrystals.
Instead of employing the traditional trial-and-error method of self-assembly that is used by nanotechnologists and which is found in nature, Torquato and his colleagues start with an exact blueprint of the nanostructure they want to build.
“In a sense this would allow you to play God, because the method creates, on the computer, new types of particles whose interactions are tuned precisely so as to yield a desired structure,” says Pablo Debenedetti, a professor of chemical engineering at Princeton.
Currently, researchers create new nanostructures by letting parts react with one other and seeing whether the result is useful. This relies on a process of self-assembly.
A news release reports on the new method proposed by Torquato and colleagues:
“We stand the problem of self-assembly on its head,” said Torquato, a professor of chemistry who is affiliated with the Princeton Institute for the Science and Technology of Materials, a multidisciplinary research center devoted to materials science. Instead of employing the traditional trial-and-error method of self-assembly that is used by nanotechnologists and which is found in nature, Torquato and his colleagues start with an exact blueprint of the nanostructure they want to build. ‘’If one thinks of a nanomaterial as a house, our approach enables a scientist to act as architect, contractor, and day laborer all wrapped up in one,” Torquato said. “We design the components of the house, such as the 2-by-4s and cement blocks, so that they will interact with each other in such a way that when you throw them together randomly they self-assemble into the desired house.” To do the same thing using current techniques, by contrast, a scientist would have to conduct endless experiments to come up with the same house. And in the end that researcher may not end up with a house at all but rather—metaphorically speaking—with a garage or a horse stable or a grain silo. While Torquato is a theorist rather than a practitioner, his ideas may have implications for nanostructures used in a range of applications in sensors, electronics and aerospace engineering. “This is a wonderful example of how asking deep theoretical questions can lead to important practical applications,” said Debenedetti. So far Torquato and his colleagues have demonstrated their concept only theoretically, with computer modeling. They illustrated their technique by considering thin films of particles. If one thinks of the particles as pennies scattered upon a table, the pennies, when laterally compressed, would normally self-assemble into a pattern called a triangular lattice. But by optimizing the interactions of the “pennies,” or particles, Torquato made them self-assemble into an entirely different pattern known as a honeycomb lattice (called that because it very much resembles a honeycomb). Why is this important? The honeycomb lattice is the two-dimensional analog to the three-dimensional diamond lattice—the creation of which is somewhat of a holy grail in nanotechnology… To create the honeycomb lattice, the researchers employed techniques of optimization, a field that has burgeoned since World War II and which is essentially the science of inventing mathematical methods to make things run efficiently. Torquato and his colleagues hope that their efforts will be replicated in the laboratory using particles called colloids, which have unique properties that make them ideal candidates to test out the theory. Paul Chaikin, a professor of physics at New York University, said he is planning to do laboratory experiments based on the work.