Investigators at the University of Michigan (U-M) say they may have found an innovative approach for organizing nanoscale particles into ordered structures. Rather than using electric or magnetic fields, their method relies solely on a natural phenomenon called entropy.
Many define entropy as disorder or chaos intrinsic to natural systems. It can best be defined as a general tendency towards equilibrium, which can only increase or stagnate, never decrease.
Computer simulations conducted at U-M demonstrate that this natural phenomenon can promote the assembly of nanoparticles into ordered, small-scale structures. The study indicated that knowing the shape of the particles beforehand allows scientists to predict the properties of the emerging structure.
Details of the new study appear in a paper entitled “Predictive Self-Assembly of Polyhedra into Complex Structures,” which is published in this week's issue of the top journal Science. In the future, it may become possible to use these findings to create advanced designer materials.
The latter could be used for applications that sound more like science fiction today, including complex camouflage for vehicles, drag-reducing hulls for future aircraft, and shape-shifting skins for a wide variety of vehicles.
“We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers. With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends,” Sharon Glotzer says.
The expert, one of the leaders on the new study, holds an appointment as a physicist and chemical engineering professor at U-M. Chemical engineering research investigator Michael Engel wrote the computer code the team used for the simulations.
Nanoparticles were found to have a tendency towards self-assembling in structures with the highest degree of entropy possible. However, this only happens if they are clustered together. If their concentration is low, they will simply spread throughout their environment uniformly.
Interestingly, when left to their own devices, the particles formed crystal-like structures in 70 percent of cases. Furthermore, these structures were composed of 52-particle structures that repeated themselves regularly.
Funds for the new investigation came from the US Department of Defense, the Department of Energy, the Deutsche Forschungsgemeinschaft and the National Science Foundation (NSF).