Nanocubes are anything but child’s play. Weizmann Institute scientists have used them to create surprisingly yarn-like strands: They showed that given the right conditions, cube-shaped nanoparticles are able to align into winding helical structures. Their results, which reveal how nanomaterials can self-assemble into unexpectedly beautiful and complex structures, were recently published in Science.
SEM image of a well-defined double helix
Dr. Rafal Klajn and postdoctoral fellow Dr. Gurvinder Singh of the Institute’s Organic Chemistry Department used nanocubes of an iron oxide material called magnetite. As the name implies, this material is naturally magnetic: It is found all over the place, including inside bacteria that use it to sense the Earth’s magnetic field.
Magnetism is just one of the forces acting on the nanoparticles. Together with the research group of Prof. Petr Král of the University of Illinois, Chicago, Klajn and Singh developed theoretical models to understand how the various forces could push and pull the tiny bits of magnetite into different formations.
“Different types of forces compel the nanoparticles to align in different ways,” says Klajn. “These can compete with one another; so the idea is to find the balance of competing forces that can induce the self-assembly of the particles into novel materials.” The models suggested that the shape of the nanoparticles is important – only cubes would provide a proper balance of forces required for pulling together into helical formations.
The researchers found that the two main competing forces are magnetism and the van der Waals force. Magnetism causes the magnetic particles to both attract and repel one another, prompting the cubic particles to align at their corners. Van der Waals forces, on the other hand, pull the sides of the cubes closer together, coaxing them to line up in a row. When these forces act together on the tiny cubes, the result is the step-like alignment that produces helical structures.
In their experiments, the scientists exposed relatively high concentrations of magnetite nanocubes placed in a solution to a magnetic field. The long, rope-like helical chains they obtained after the solution was evaporated were surprisingly uniform. They repeated the experiment with nanoparticles of other shapes but, as predicted, only cubes had just the right physical shape to align in a helix. Klajn and Singh also found that they could get chiral strands – all wound in the same direction – with very high particle concentrations in which a number of strands assembled closely together. Apparently the competing forces can “take into consideration” the most efficient way to pack the strands into the space.
Although the nanocube strands look nice enough to knit, Klajn says it is too soon to begin thinking of commercial applications. The immediate value of the work, he says, is that it has proven a fundamental principle of nanoscale self-assembly. “Although magnetite has been well-studied – also its nanoparticle form – for many decades, no one has observed these structures before,” says Klajn. “Only once we understand how the various physical forces act on nanoparticles can we begin to apply the insights to such goals as the fabrication of previously unknown, self-assembled materials.”
Yivsam Azgad | Eurek Alert!
How to become a T follicular helper cell
31.07.2015 | La Jolla Institute for Allergy and Immunology
Heating and cooling with light leads to ultrafast DNA diagnostics
31.07.2015 | University of California - Berkeley
Using ultracold atoms trapped in light crystals, scientists from the MPQ, LMU, and the Weizmann Institute observe a novel state of matter that never thermalizes.
What happens if one mixes cold and hot water? After some initial dynamics, one is left with lukewarm water—the system has thermalized to a new thermal...
Physicists from Regensburg and Marburg, Germany have succeeded in taking a slow-motion movie of speeding electrons in a solid driven by a strong light wave. In the process, they have unraveled a novel quantum phenomenon, which will be reported in the forthcoming edition of Nature.
The advent of ever faster electronics featuring clock rates up to the multiple-gigahertz range has revolutionized our day-to-day life. Researchers and...
Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.
Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight
A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...
Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.
By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...
23.07.2015 | Event News
10.07.2015 | Event News
25.06.2015 | Event News
31.07.2015 | Trade Fair News
31.07.2015 | Transportation and Logistics
31.07.2015 | Physics and Astronomy