A team of researchers from the University of Colorado Boulder has managed to find a new phase of matter, a liquid state that was initially suggested in the 1910s.
The scientists used a liquid crystal compound to find a new ‘ferroelectric nematic’ phase that could pioneer an entirely new class of materials and technology progresses. There are lots of phases if liquid crystal, but one of the most common is the nematic stage; this is the phase that allows liquid crystal to display technology.
Order and Disorder
Such phases are determined by how the molecules act within the material. The liquid crystal compound is made up of organic molecules resembling a rod with positively and negatively charged ends, similar to small bar magnets. In a nematic phase, these molecules are split with half aiming one way, and the other pointing the other, in a more or less random arrangement.
In the 1910s, two physicists, Peter Debye and Max Born suggested another scenario for the molecular pattern. As per their two papers, published in 1912 and 1916, respectively, it should be feasible to create a liquid crystal in such a way that the molecules end up in a state of polar order.
This means there should be definite patches where the molecules’ poles are all pointing in the same direction, and this direction can be changed by using external electric fields. This property is well-known in solid crystals, and it is called ferroelectricity. However, even though the ferroelectric behavior had been theorized in nematic liquid crystal, it has remained unclear.
But in 2017, a team of experts reported they had created a new rod-shaped organic molecule that could be useful for liquid crystal, namely the compound RM734. In subsequent studies, RM734 showed some rather unusual behaviors.
More particularly, while RM734 acted like a normal nematic liquid crystal phase at higher temperatures, its behavior was more peculiar when exposed to lower temperatures; namely, the molecular position was observed to deform in a ‘splay’ arrangement.
A New Class of Nematic Physics
This is where the new research steps in. The team of physicists were examining RM734 under a polarized light microscope and employed a weak electric field to try to cause the splay nematic phase. The splay pattern did not appear, but patches or bright colors around the margins of the cell having the RM734 liquid crystal did.
“It was like connecting a light bulb to voltage to test it but finding the socket and hookup wires glowing much more brightly instead,” said physicist Noel Clark of UC Boulder.
More tests unveiled the fact that this state of RM734 was between 100 and 1,000 times more receptive to external electric fields than other nematic liquid crystals, which implied that the molecules show polar order. When cooled from higher temperatures, the arranged patches showed up by their own means in the sample, with almost all the molecules in each patch aiming in the same direction.
“That confirmed that this phase was, indeed, a ferroelectric nematic fluid,” Clark said.
The team is still not completely convinced how or why RM734 shows this ferroelectric nematic phase, but its existence implies that more ferroelectric fluids may be possible, which are yet to be found. This can also open doors to new nematic physics and new technology, such as display advances and computer memory.
The research paper has been published in PNAS.