Liquid crystals for fast switching devices

Date:
December 6, 2021
Source:
Helmholtz-Zentrum Berlin fu"r Materialien und Energie
Summary:
An international team has investigated a newly synthesized liquid-
crystalline material that promises applications in optoelectronics.

Simple rod-shaped molecules with a single center of chirality self-
assemble into helical structures at room temperature. Using soft
X-ray resonant scattering at BESSY II, the scientists have now
been able to determine the pitch of the helical structure with
high precision. Their results indicate an extremely short pitch
at only about 100 nanometres which would enable applications with
particularly fast switching processes.



FULL STORY ========================================================================== 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
include flat screens and digital displays. They are based on pixels of
liquid crystals whose optical properties can be switched by electric
fields.


==========================================================================
Some liquid crystals form the so-called cholesteric phases: the molecules
self- assemble into helical structures, which are characterised by
pitch and 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 Dr.

Alevtina Smekhova, physicist at HZB and first author of the study,
which has now been published in Soft Matter.

Simple molecular chain In this work, she and partners from the
Academies of Sciences in Prague, Moscow and Chernogolovka investigated
a liquid crystalline cholesteric compound called EZL10/10, developed
in Prague. "Such cholesteric phases are usually formed by molecules
with several chiral centres, but here the molecule has only one chiral
centre," explains Dr. Smekhova. It is a simple molecular chain with one
lactate unit.

Ultrashort pitch At BESSY II, the team has now examined this compound
with soft X-ray light and determined the pitch and space ordering of the spirals. This was the shortest up-to-date reported value of the pitch:
only 104 nanometres! This is twice as short as the previously 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.

Outlook "This very short pitch makes the material unique and promising
for optoelectronic devices with very fast switching times," Dr. Smekhova
points out. In addition, the EZ110/10 compound is thermally and chemically stable and can easily be further varied to obtain structures with
customised pitch lengths.

========================================================================== Story Source: Materials provided by Helmholtz-Zentrum_Berlin_fu"r_Materialien_und_Energie.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alevtina Smekhova, Vladimi'ra Novotna', Ladislav Fekete, Radu
Abrudan,
Mattis Fondell, Věra Hamplova', Boris
I. Ostrovskii. Ultra-short helix pitch and spiral ordering
in cholesteric liquid crystal revealed by resonant soft X-ray
scattering. Soft Matter, 2021; DOI: 10.1039/ D1SM01543E ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211206113049.htm

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