Scientists have found out how magnetic nanoparticles self-assemble, a discovery that could help them develop revolutionary new materials.
Image: Megan Strand/University of Illinois at Chicago
Researchers have long been excited about turning nanoparticles and their unique properties into materials, which, just to name a few potential applications, could be used to improve solar panels and create better touch screens.
But there’s a problem - nanoparticles are notoriously difficult to organise into useful arrangements.
However, nanoparticles of magnetite (Fe3O4), the most abundant magnetic material on Earth, are known to self-assemble into fine compass needles inside animals such as birds to help them navigate. So researchers from the University of Illinois at Chicago in the US and the Weizmann Institute of Science in Israel decided to study how these nanoparticles self-assemble, and what influences their shape.
Their results are published today in Science, and reveal that, in the presence of a magnetic field, magnetic nanoparticles will assemble into helical, DNA-like chains.
Surprisingly, the helices were chiral, which means they’re either left- or right-handed - even though magnetite nanoparticles themselves don’t show any chirality. By modelling the self-assembly process, the researchers discovered that the nanoparticles self-assemble into chiral helices because of a range of competing forces acting on them - ranging from the magnetic force to temperature.
A University of Illinois at Chicago press release explains
“In the presence of an external magnetic field, the superparamagnetic nanocubes - which are randomly magnetic and can flip with temperature changes - became tiny magnets with different symmetries of the competing forces acting between them. As a result, when two cubes are face-to-face, they tend to tilt with respect to each other, forming a small angle to the right or left - the seed of a chiral helix, as more nanocubes line up with the first two.”
Knowing the carefully controlled conditions that cause these nanoparticles to self-assemble could greatly help researchers work out how to use them to make functional materials

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