Breaking Coloumb's law: Scattered X-ray results

Skip to Navigation

Ezine

  • Published: Oct 1, 2017
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Breaking Coloumb's law: Scattered X-ray results

Breaking the law

X-ray scattering studies have been used to show how the previously immutable Coloumb's law that says electrical charges attract might be broken. The discovery could pave way the way to a new type of battery, new water treatment technology, and alternative energy supply.

X-ray scattering studies have been used to show how the previously immutable Coloumb's law that says electrical charges attract might be broken; at least in ionic liquids confined in a nanoscopic space. The discovery could pave way the way to a new type of battery, new water treatment technology, and alternative energy supply.

French physicist Charles-Augustin de Coulomb first published his law of electrostatic attraction in 1784, laying down the basic principle of electrochemistry for the centuries thereafter and countless discoveries and applications. At its heart lies the fact that opposite charges attract and his inverse square law dictates the magnitude of the attractive force between those particles. Particles of the same charge repel and the repulsive force, likewise, is given by his law. Now, an international team of researchers has found a way to side step this principle, partially at least by preventing Coulombic ordering of ionic liquids confined in carbon nanopores. The normal Coulombic ordering seen as particles of opposite charge attract can break down in this environment.

Mark Biggs of Loughborough University, UK, and colleagues suggest that disrupting the natural order of charged particles could be critical to the development of electrical energy storage devices such as a new class of batteries and the rapidly charging supercapacitors needed to make electric vehicles more attractive and to provide backup to wind power on still days and solar when it is cloudy. The same broken principles might also be exploited in a new efficient approach to water treatment that uses ions packed into nanoporous materials rather than conventional membranes.

Like to like

Biggs and his colleagues carried out three-dimensional, 3D, molecular modelling of the systems to allow their colleagues to interpret with greater precision the X-ray scattering experimental data obtained from practical systems in the laboratory. "Using 3D molecular models, we can determine from the experimental X-ray scattering data how the positively and negatively charged ions pack relative to each other inside the nanopores," Biggs explains. "Without this 3D molecular modelling ability, we would not have been able to discover the non-Coulombic packing."

Normally ions in an ionic liquid arrange themselves according to the alternating positive-negative pattern of Coulombic ordering. The team observed this with carbon nanotubes of larger diameter. However, where the carbon nanotubes had such small bores that they could only hold a single layer of ions, then the team saw pairs of negative ions and pairs of positive ions occurring widely in the system, in stark contravention of Coloumb's law, it seems. "In this state, the Coulombic ordering of the liquid is broken," the team explains. "Ions of the same charge neighbour each other due to a screening of their electrostatic interactions by the images charges induced in the carbon pore walls." The effect is more pronounced if a charge is applied to the carbon as might be the case in charging and discharging a supercapacitor. "Our results suggest the existence of a molecular-scale mechanism that reduces the Coulombic repulsion energy between co-ions that become closer to each other," the team says, such a phenomenon hints at a new approach to building supercapacitors.

Supercapacitors

According to Drexel's Yury Gogotsi, the discovery brings us closer to using ionic liquids in batteries. "We can get safer batteries and supercapacitors when using ionic liquid electrolytes because the ionic liquids are not flammable like the electrolyte solutions currently used in these devices." He adds that there is another benefit in that there is no need to add a solvent as the electrolyte is its own solvent effectively and so the entire volume is occupied by ions.

Others involved in this work include scientists from Shinshu University, in Japan; Sabatier University, in Toulouse, Sorbonne University, in Paris; the French Research Network on Electrochemical Energy Storage, Drexel University, in Philadelphia, USA, and the University of Adelaide, in Australia.

Related Links

Nature Mater 2017, online: "Partial breaking of the Coulombic ordering of ionic liquids confined in carbon nanopores."

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Follow us on Twitter!

Social Links

Share This Links

Bookmark and Share

Microsites

Suppliers Selection
Societies Selection

Banner Ad

Click here to see
all job opportunities

Copyright Information

Interested in separation science? Visit our sister site separationsNOW.com

Copyright © 2017 John Wiley & Sons, Inc. All Rights Reserved