Manipulation of the nanoscale heliconical structure of a twist-bend nematic material with polarized light

Rapid Communication
Open Access

Manipulation of the nanoscale heliconical structure of a twist-bend nematic material with polarized light

C. Feng, J. Feng, R. Saha, Y. Arakawa, J. Gleeson, S. Sprunt, C. Zhu, and A. Jákli

Phys. Rev. Research 2, 032004(R) – Published 2 July 2020

Abstract

The effect of polarized violet light on the alignment and the heliconical pitch of a liquid crystal dimer containing both sulfur atoms and an azo linkage has been studied by tender resonant x-ray scattering. The results provide evidence of the manipulation of the nanoscale heliconical structure by polarized light. In addition to the bulk alignment of the heliconical nanostructure, the value of the heliconical pitch can be varied as well. After turning the light on, an increase of the pitch is observed in two steps. The increase with a subsecond timescale is attributed to the reduced heliconical order related to trans-cis photoisomerization. This is followed by a smaller increase over a 10-s timescale, which is likely related to the annihilation of defects. After turning the light off, the pitch first decreases within a few seconds to a value larger than the original (before illumination), and then relaxes further on a much longer (hours) timescale.

Received 8 May 2020
Accepted 16 June 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.032004

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Chiral symmetry Dynamical phase transitions Twist deformation

Polymers & Soft Matter

Authors & Affiliations

C. Feng ^1,2, J. Feng ², R. Saha ⁴, Y. Arakawa ³, J. Gleeson⁴, S. Sprunt ^1,4, C. Zhu^2,*, and A. Jákli ^1,4,†

¹Chemical Physics Interdisciplinary Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
²Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California 94720, USA
³Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi, 441-8580, Japan
⁴Department of Physics, Kent State University, Kent, Ohio 44242, USA

^*chenhuizhu@lbl.gov
^†ajakli@kent.edu

Article Text

Click to Expand

References

Click to Expand

Issue

Vol. 2, Iss. 3 — July - September 2020

Subject Areas

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Molecular structure and polarized optical microscopy (POM) textures of CNAzoS7SCB. (a) Molecular structure and phase sequences determined by POM with crossed polarizers (see crossed arrows on the top right). (b) POM textures of a 5-μm cell at 2 °C and 7 °C below the $N − N_{T B}$ transition temperature before (left), during (middle), and after (right) the sample is illuminated by a 385-nm-wavelength, $\sim 50 − mW / c m^{2}$ intensity unpolarized LED light. Thinner stripes before and after illumination are parallel to the rubbing direction of the planar alignment polyimide coating [double headed white arrow shown in the top left picture of (b)].
Reuse & Permissions
Figure 2
Temperature dependences of the heliconical pitch of CNAzoS7SCB measured in dark (black dots) and during about $50 mW / c m^{2}$ intensity 405-nm-wavelength polarized laser light (hollow and solid blue square for aligned and unaligned domains, respectively). Typical 2D scattered patterns in dark state at $Δ T = 5^{\circ} C$ and during violet light illumination at $Δ T = 3^{\circ} C$ are shown in insets (a), (b), respectively. Overlaid on inset (b) is the schematic structures of the aligned and unaligned heliconical domains. The approximate shapes of the molecules in the dark trans and the light induced cis states are shown below the data points. The darker blue strip enclosed by black dotted lines in the horizontal direction is the shadow of the beam stop that was between the detector and the sample, i.e., not right in front of the detector.
Reuse & Permissions
Figure 3
Representative 2D TReXS scattering patterns at 2 ° C, 3 ° C, and 5 °C below the dark $N − N_{T B}$ phase transition before (left), during 3s of illumination (middle), and at different times after the polarized light turned off (right). Top row: $Δ T = T_{N − N_{T B}} − T = 2^{\circ} C$ ; middle row: $Δ T = 3^{\circ} C$ ; bottom row: $Δ T = 5^{\circ} C$ .
Reuse & Permissions
Figure 4
Time dependence of the wave number $q$ after the polarized violet light is turned on at $t = 0$ and off at $t = 36 s$ . Note the smallest time difference between two consecutive measurements was 3 s, as the TReXS exposure time was 2 s. Green dotted arrows for $Δ T = 2^{\circ} C$ indicate that the wave number decreases below $q = 0.2 n m^{- 1}$ in less than 3 s after turning the light on, and increases above $0.2 n m^{- 1}$ after turning the light off. Solid symbols and continuous lines refer to unaligned domains, whereas open symbols with dotted lines describe behavior of aligned domains. The blue dotted and continuous and black dotted lines after the light turned on at $Δ T = 3^{\circ} C$ and 5 °C are fit equations using double exponential functions. The black dotted line at $Δ T = 5^{\circ} C$ after the light is turned off is a fit to a single exponential. Other lines are only a guide to the eye.
Reuse & Permissions

Physical Review Research