Post by Bi0hazard on Sept 14, 2011 0:57:52 GMT -6
Exotic Quasicrystal Structures May Be More Normal Than Assumed
Different nanoparticles can self-assemble into complex quasicrystal arrangements
URL: www.scientificamerican.com/article.cfm?id=quasicrystals-self-assemble
Quasicrystals are a relative newcomer to the field of materials science, having been discovered just 25 years ago. Nudging their way between amorphous solids such as glass and crystals such as quartz, the structures exhibit an ordered structure like crystals do, but their uniqueness lies in the fact that the ordered arrangement does not repeat—that is to say, it is not periodic.
Quasicrystals also lack translational symmetry. To give a two-dimensional analogue, the pattern cannot be shifted laterally without changing its appearance (unlike, say, an infinitely repeating checkerboard pattern, which can be shifted two squares in any direction and retain its original format).
Since their discovery in 1984 quasicrystals have been found in many highly synthesized materials and in one mineral of apparently natural origin—an alloy of aluminum, copper and iron found in Russia. But a study in this week's Nature shows that quasicrystals may be a fairly natural way for objects to pack themselves together and may not require much manipulation to take shape. (Scientific American is part of the Nature Publishing Group.) A team led by University of Chicago physicist Dmitri Talapin reports that various pairings of nanoparticles, when mixed in solution and left to evaporate, coalesce into quasicrystal structures.
That a variety of particle pairs—two different iron oxides mixed with gold as well as lead sulfide paired with palladium—can successfully self-assemble into quasicrystals suggests that it may be a more common arrangement than had been thought, the study's authors wrote. The only real common ground in the pairings seemed to be a relatively consistent ratios among the sizes of the different nanoparticles. "These structures can self-assemble without much human intervention," Talapin says. "All [researchers] need is to properly design the building blocks."
In 2006 Talapin and a group of researchers, some of whom were also involved with the new study, showed how nanoparticles can self-assemble into more than a dozen different periodic lattice structures. The next step, he says, was to move beyond the periodic "to try making some really weird creatures—and quasicrystals are a quite natural candidate along those lines."
A solution of spherical nanoparticles of iron oxide and gold did the trick, but Talapin and his colleagues wanted to know if quasicrystalline structures are a general packing arrangement or if the team had simply lucked out in their choice of ingredients. So they tried other combinations of particles and got the same result. "We found that it's really a law of nature rather than a unique combination of many parameters that just line up in a lucky way," Talapin says.
Alfons van Blaaderen, a physicist at Utrecht University in the Netherlands who wrote a commentary in Nature on the new research, says that quasicrystals indeed appear to be more generic than had been thought. But he notes that in the absence of simulations or theory to show how the structures are forming, it is impossible to completely rule out a wild stroke of luck in the Talapin group's recipes. "It could just be a weird coincidence" that the various mixtures of particles self-assembled into quasicrystals, van Blaaderen says, adding that such a coincidental result is highly unlikely.
Van Blaaderen's group is working on replicating the findings with larger particles, which would allow researchers to observe the structures taking shape in real-time. Such a window into the quasicrystal formation process could help materials scientists understand what is necessary to build structures incorporating characteristics of both amorphous solids and crystals.
Whatever the case, Talapin and his colleagues have added to a growing number of regimes in which quasicrystals, a total unknown just a few decades ago, can form. "Now we see these materials are much less weird than we used to believe," he says.
Different nanoparticles can self-assemble into complex quasicrystal arrangements
URL: www.scientificamerican.com/article.cfm?id=quasicrystals-self-assemble
Quasicrystals are a relative newcomer to the field of materials science, having been discovered just 25 years ago. Nudging their way between amorphous solids such as glass and crystals such as quartz, the structures exhibit an ordered structure like crystals do, but their uniqueness lies in the fact that the ordered arrangement does not repeat—that is to say, it is not periodic.
Quasicrystals also lack translational symmetry. To give a two-dimensional analogue, the pattern cannot be shifted laterally without changing its appearance (unlike, say, an infinitely repeating checkerboard pattern, which can be shifted two squares in any direction and retain its original format).
Since their discovery in 1984 quasicrystals have been found in many highly synthesized materials and in one mineral of apparently natural origin—an alloy of aluminum, copper and iron found in Russia. But a study in this week's Nature shows that quasicrystals may be a fairly natural way for objects to pack themselves together and may not require much manipulation to take shape. (Scientific American is part of the Nature Publishing Group.) A team led by University of Chicago physicist Dmitri Talapin reports that various pairings of nanoparticles, when mixed in solution and left to evaporate, coalesce into quasicrystal structures.
That a variety of particle pairs—two different iron oxides mixed with gold as well as lead sulfide paired with palladium—can successfully self-assemble into quasicrystals suggests that it may be a more common arrangement than had been thought, the study's authors wrote. The only real common ground in the pairings seemed to be a relatively consistent ratios among the sizes of the different nanoparticles. "These structures can self-assemble without much human intervention," Talapin says. "All [researchers] need is to properly design the building blocks."
In 2006 Talapin and a group of researchers, some of whom were also involved with the new study, showed how nanoparticles can self-assemble into more than a dozen different periodic lattice structures. The next step, he says, was to move beyond the periodic "to try making some really weird creatures—and quasicrystals are a quite natural candidate along those lines."
A solution of spherical nanoparticles of iron oxide and gold did the trick, but Talapin and his colleagues wanted to know if quasicrystalline structures are a general packing arrangement or if the team had simply lucked out in their choice of ingredients. So they tried other combinations of particles and got the same result. "We found that it's really a law of nature rather than a unique combination of many parameters that just line up in a lucky way," Talapin says.
Alfons van Blaaderen, a physicist at Utrecht University in the Netherlands who wrote a commentary in Nature on the new research, says that quasicrystals indeed appear to be more generic than had been thought. But he notes that in the absence of simulations or theory to show how the structures are forming, it is impossible to completely rule out a wild stroke of luck in the Talapin group's recipes. "It could just be a weird coincidence" that the various mixtures of particles self-assembled into quasicrystals, van Blaaderen says, adding that such a coincidental result is highly unlikely.
Van Blaaderen's group is working on replicating the findings with larger particles, which would allow researchers to observe the structures taking shape in real-time. Such a window into the quasicrystal formation process could help materials scientists understand what is necessary to build structures incorporating characteristics of both amorphous solids and crystals.
Whatever the case, Talapin and his colleagues have added to a growing number of regimes in which quasicrystals, a total unknown just a few decades ago, can form. "Now we see these materials are much less weird than we used to believe," he says.