Liquid crystal cells on the modified sample holder, which was used in the real experiment. This modified sample holder is mounted within the ALICE chamber at BESSY II. Image: A. Smekhova/HZB.Liquid crystals are not solid, but some of their physical properties are directional – like in a crystal. This is because their molecules can arrange themselves into certain patterns. The best-known applications of liquid crystals include in flat screens and digital displays, which utilize pixels of liquid crystals whose optical properties can be switched by electric fields.
Some liquid crystals form so-called cholesteric phases: the molecules self-assemble into helical structures, which are characterized by pitch and can rotate either to the right or to the left. "The pitch of the cholesteric spirals determines how quickly they react to an applied electric field," explains Alevtina Smekhova, a physicist at Helmholtz-Zentrum Berlin (HZB) in Germany.
In this work, Smekhova and researchers from the Academies of Sciences in Prague in the Czech Republic and Moscow in Russia investigated a liquid crystalline cholesteric compound called EZL10/10, developed by the Prague researchers, and discovered that it has the shortest known pitch. The report their findings in a paper in Soft Matter.
"Such cholesteric phases are usually formed by molecules with several chiral centres, but here the molecule has only one chiral centre," explains Smekhova. It is a simple molecular chain with one lactate unit.
At BESSY II, the team examined this compound with soft X-ray light and determined the pitch and space ordering of the spirals. This revealed that EZL10/10 has the shortest reported value for the pitch – just 104nm. This is twice as short as the previous shortest known pitch of spiral structures in liquid crystals. Further analysis showed that in this material the cholesteric spirals form domains with characteristic lengths of about five pitches.
"This very short pitch makes the material unique and promising for optoelectronic devices with very fast switching times," Smekhova says. In addition, the EZ110/10 compound is thermally and chemically stable, and can easily be further modified to obtain structures with customized pitch lengths.
This story is adapted from material from Helmholtz-Zentrum Berlin, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.