Materials made from nanoparticles hold promise for myriad applications, from improved solar energy production to perfect touch screens. The challenge in creating these wonder-materials is organizing the nanoparticles into orderly arrangements.
Nanoparticles of magnetite, the most abundant magnetic material on earth, are found in living organisms from bacteria to birds. Nanocrystals of magnetite self-assemble into fine compass needles in the organism that help it to navigate.
Collaborating with nanochemists led by Rafal Klajn at the Weizmann Institute of Science in Israel, who found that magnetite nanocubes can self-assemble into helical superstructures under certain conditions, University of Illinois at Chicago theoretical chemist Petr Kral and his students simulated the phenomenon and explained the conditions under which it can occur. The joint study is online in Science Express in advance of print in the Sept. 5 issue of Science.
The Weizmann researchers dissolved the nanocrystals and exposed the solution to an external magnetic field. As the solution evaporated, helical chains of nanoparticles formed. Surprisingly, the spiral helices were chiral -- that is, either left- or right-handed -- despite the fact that the nanoparticles themselves are not chiral. Densely packed assemblies of helices tended to adopt the same handedness.
Kral's UIC team modeled the self-assembly to determine how helices formed in their collaborators' experiments -- and why the helices had chirality.
They found that the self-assembly into chiral helices is the result of the competing forces acting on them — Zeeman force from the external magnetic field, dipole-dipole magnetic force, magneto-anisotropic directional force, weakly attractive van der Waals forces, and others. The chemistry of the nanoparticle ligands, the solvent, and temperature may also play a role.
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.
Kral's analysis used a Monte Carlo computer algorithm, which relies on repeated random sampling, running simulations many times over.
"We had to write a new, efficient Monte Carlo computer code describing all the necessary terms, all the values, and then explain how the highly unusual behavior that Klajn observed – the helices' self-assembly – happens," Kral said.
Gurvinder Singh of the Weizmann Institute is first author of the paper. Elijah Gelman of the Weizmann Institute, and Henry Chan, Artem Baskin and Nikita Repnin of UIC are co-authors on the study.
The work was supported by the Israel Science Foundation grant 1463/11, the G. M. J. Schmidt-Minerva Center for Supramolecular Architectures, the Minerva Foundation with funding from the Federal German Ministry for Education and Research, National Science Foundation Division of Materials Research grant 1309765 and the American Chemical Society Petroleum Research Fund grant 53062-ND6.
Jeanne Galatzer-Levy | Eurek Alert!
Clay nanotube-biopolymer composite scaffolds for tissue engineering
02.05.2016 | Kazan Federal University
Personal cooling units on the horizon
29.04.2016 | Penn State
Using an ultra fast-scanning atomic force microscope, a team of researchers from the University of Basel has filmed “living” nuclear pore complexes at work for the first time. Nuclear pores are molecular machines that control the traffic entering or exiting the cell nucleus. In their article published in Nature Nanotechnology, the researchers explain how the passage of unwanted molecules is prevented by rapidly moving molecular “tentacles” inside the pore.
Using high-speed AFM, Roderick Lim, Argovia Professor at the Biozentrum and the Swiss Nanoscience Institute of the University of Basel, has not only directly...
If a person pushes a broken-down car alone, there is a certain effect. If another person helps, the result is the sum of their efforts. If two micro-particles are pushing another microparticle, however, the resulting effect may not necessarily be the sum their efforts. A recent study published in Nature Communications, measured this odd effect that scientists call “many body.”
In the microscopic world, where the modern miniaturized machines at the new frontiers of technology operate, as long as we are in the presence of two...
Researchers from the Max Planck Institute Stuttgart have developed self-propelled tiny ‘microbots’ that can remove lead or organic pollution from contaminated water.
Working with colleagues in Barcelona and Singapore, Samuel Sánchez’s group used graphene oxide to make their microscale motors, which are able to adsorb lead...
Neutron scattering and computational modeling have revealed unique and unexpected behavior of water molecules under extreme confinement that is unmatched by any known gas, liquid or solid states.
In a paper published in Physical Review Letters, researchers at the Department of Energy's Oak Ridge National Laboratory describe a new tunneling state of...
Honeycomb structures as the basic building block for industrial applications presented using holo pyramid
Researchers of the Alfred Wegener Institute (AWI) will introduce their latest developments in the field of bionic lightweight design at Hannover Messe from 25...
27.04.2016 | Event News
15.04.2016 | Event News
12.04.2016 | Event News
03.05.2016 | Physics and Astronomy
03.05.2016 | Life Sciences
03.05.2016 | Physics and Astronomy