23 September 2016

High field changes phase transitions in “shape-shifting” molecules

Using lasers in the split helix magnet (above), scientists observed high magnetic fields change the shape of molecules, thereby changing some of their properties. Using lasers in the split helix magnet (above), scientists observed high magnetic fields change the shape of molecules, thereby changing some of their properties.

With a sufficiently high magnetic field, scientists can manipulate certain phase transitions in some molecules, a discovery that hints at future technological applications.

First, some background

Between commonly known phases of liquids and solids exists another phase of matter, liquid crystals. Like the phase transition we witness when an ice cube melts, the transition from liquid to liquid crystal can be influenced by both internal and external factors. Internally, the shape and temperature of molecules that make up the liquid affect whether and how it transitions into this "exotic" state. Externally, scientists can apply electric or magnetic fields to the molecules to see if they can also influence the phase transition.

In previous experiments that studied this phase transition, scientists examined a dimer, a molecule composed of two identical molecules with a bendy connector between them (not unlike a nunchaku fighting stick). Scientists found that when this dimer was placed in magnetic fields up to 10 teslas, the temperature at which it turned from a liquid into a liquid crystal increased. But that phase transition temperature rose only by a fraction of a degree Celsius.

What did scientists discover?

Scientists conducted a similar experiment at the MagLab, but this time in a much higher magnetic field of 22 teslas. The result was a dramatic increase in the transition temperature of as much as 13 degrees Celsius.

Scientists believe the high magnetic field increases the angle between the dimer's molecules, effectively straightening them out (see illustration above). This shape shifting, in turn, can change the phase transition temperature. As the molecules transition from liquid to liquid crystals, they morph from a disordered jumble to a neatly stacked, ordered state (see illustration above).

Why is this important?

Molecules with tailor-able shape and stiffness often form exotic states of matter. However, the details of just how that happens can be difficult to discern experimentally. The ability to control the exotic state of matter with an external magnetic field has exciting potential technological applications ranging from materials science to electro-optics.

Who did the research?

S. M. Salili1, M. G. Tamba2, S. N. Sprunt1 ,C. Welch3, G. H. Mehl3, A. Jákli1, and J. T. Gleeson1

1Kent State University; 2Otto von Guericke University, 3University of Hull

Why did they need the MagLab?

THE TOOLS THEY USED

This research was conducted in the 25T Split Helix Magnet (cell 5) at the MagLab's DC Field Facility.

These experiments were conducted in the world-unique 25-tesla split helix magnet, which is open in the middle. This set-up allows scientists doing optics experiments to shoot lasers at a sample and to expose it to a high magnetic field at the same time. Observing the angle of the laser beams, the researchers were able to study how the molecules changed shape as the magnetic field changed.

Details for scientists

Funding

This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); J.T. Gleeson, S.N. Sprunt, A. Jákli, G.H. Mehl (EPRSC EP/J004480/1)


For more information, contact Tim Murphy.

Details

  • Research Area: Chemistry
  • Research Initiatives: Materials
  • Facility / Program: DC Field
  • Year: 2016
Last modified on 23 September 2016