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Title: Field induced heliconical structure of cholesteric liquid crystal

Abstract

A diffraction grating comprises a liquid crystal (LC) cell configured to apply an electric field through a cholesteric LC material that induces the cholesteric LC material into a heliconical state with an oblique helicoid director. The applied electric field produces diffracted light from the cholesteric LC material within the visible, infrared or ultraviolet. The axis of the heliconical state is in the plane of the liquid crystal cell or perpendicular to the plane, depending on the application. A color tuning device operates with a similar heliconical state liquid crystal material but with the heliconical director axis oriented perpendicular to the plane of the cell. A power generator varies the strength of the applied electric field to adjust the wavelength of light reflected from the cholesteric liquid crystal material within the visible, infrared or ultraviolet.

Inventors:
; ; ;
Publication Date:
Research Org.:
Kent State Univ., Kent, OH (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1366492
Patent Number(s):
9,690,161
Application Number:
14/812,397
Assignee:
KENT STATE UNIVERSITY CHO
DOE Contract Number:
FG02-06ER46331
Resource Type:
Patent
Resource Relation:
Patent File Date: 2015 Jul 29
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Lavrentovich, Oleg D., Shiyanovsii, Sergij V., Xiang, Jie, and Kim, Young-Ki. Field induced heliconical structure of cholesteric liquid crystal. United States: N. p., 2017. Web.
Lavrentovich, Oleg D., Shiyanovsii, Sergij V., Xiang, Jie, & Kim, Young-Ki. Field induced heliconical structure of cholesteric liquid crystal. United States.
Lavrentovich, Oleg D., Shiyanovsii, Sergij V., Xiang, Jie, and Kim, Young-Ki. 2017. "Field induced heliconical structure of cholesteric liquid crystal". United States. doi:. https://www.osti.gov/servlets/purl/1366492.
@article{osti_1366492,
title = {Field induced heliconical structure of cholesteric liquid crystal},
author = {Lavrentovich, Oleg D. and Shiyanovsii, Sergij V. and Xiang, Jie and Kim, Young-Ki},
abstractNote = {A diffraction grating comprises a liquid crystal (LC) cell configured to apply an electric field through a cholesteric LC material that induces the cholesteric LC material into a heliconical state with an oblique helicoid director. The applied electric field produces diffracted light from the cholesteric LC material within the visible, infrared or ultraviolet. The axis of the heliconical state is in the plane of the liquid crystal cell or perpendicular to the plane, depending on the application. A color tuning device operates with a similar heliconical state liquid crystal material but with the heliconical director axis oriented perpendicular to the plane of the cell. A power generator varies the strength of the applied electric field to adjust the wavelength of light reflected from the cholesteric liquid crystal material within the visible, infrared or ultraviolet.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 6
}

Patent:

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  • Electric fields can induce motion of polymer cholesteric liquid crystal (pCLC) flakes suspended in a fluid medium. The platelet-shaped pCLC flakes with a Grandjean texture show strong selective reflection when lying flat in the plane of a conventional cell. As their orientation with respect to normally incident light changes, their selective reflection color shifts toward the blue and diminishes until the flakes are no longer easily visible beyond 7-12{sup o} of rotation. Reproducibility and control of motion has been observed in moderately conductive host fluid. Flakes in such hosts do not respond to a DC electric field, but they rotatemore » 90{sup o} in an AC field within a given frequency band. The response times and frequency regions for motion depend partially on the field magnitude, the dielectric properties of the host fluid and the flake geometry. We observe flakes reorienting in less than 500 ms in an electric field of 0.17 Vrms/mm, while subsecond reorientation is seen in fields as low as 5 x 10-2 Vrms/mm. This response time is comparable with typical electronic-paper applications, but with a significantly lower electric field. Displays using pCLC flakes would not require backlighting, sheet polarizers, color filters or alignment layers. Numerous additional applications for pCLC flakes are envisioned, including filters, polarizers, and spatial light modulators.« less
  • The motion of highly dielectric polymer cholesteric liquid crystal (PCLC) flakes suspended in a host fluid can be controlled with an ac electric field. The electric field acts to induce a dipole moment on the flake due to interfacial, or Maxwell-Wagner, polarization. Theoretical modeling of PCLC flakes as oblate spheroids shows that the flakes will reorient to align one of the two major axes parallel to the electric field. The theory also supports the observed dependence of the particle reorientation time on the electric-field magnitude, frequency, and particle shape. A PCLC flake's orientation determines its ability to reflect light ofmore » a specific wavelength and circular polarization. The ability to switch the position of PCLC flakes with an electric field has implications for electro-optic devices and display applications.« less
  • This paper describes formation of 2-D hexagonal structures with a periodicity ~0.5-0.8 um in the defects of thin films of cholesteric oligomeric liquid crystals prepared by the evaporation of the solvent from the oligomer solution on the substrate. These regular arrays were observed by scanning near-field optical and concurrent atomic force microscopy. The mechanisms considered are both Benard-Marangoni and buoyancy conventions induced by solvent evaporation and air-bubble creation around the condensed water droplets from the air during evaporative cooling. Hexagonal structures prepared by this method can be used in photonic devices for emission enhancement, for instance, in liquid crystal lasersmore » and single photon sources with oligomeric liquid crystal hosts.« less
  • The behavior of polymer cholesteric liquid crystal (PCLC) flakes suspended in silicone oil host fluids has been explored in the presence of a direct-current electric field. In addition to “neat” (undoped) flakes, the PCLC material was doped with either conductive, carbon-based particles or highly dielectric inorganic particles to modify the dielectric properties of the resulting PCLC flakes. Doping with conductive particles produced flakes with a net charge, and they exhibited either translational or rotational motion depending on both the distribution of dopant within the flake and the dielectric characteristics of the host fluid. Flakes doped with titania (TiO2) particles reorientedmore » 90º when suspended in a host fluid with a differing dielectric permittivity« less