scholarly journals Engineering the Uniform Lying Helical Structure in Chiral Nematic Liquid Crystals: From Morphology Transition to Dimension Control

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 414
Author(s):  
Zhixuan Jia ◽  
Tejal Pawale ◽  
Guillermo I. Guerrero-García ◽  
Sid Hashemi ◽  
José A. Martínez-González ◽  
...  

Chiral nematic liquid crystals (CLCs), with a unique helix structure, have attracted immense recognition over the last few decades owing to the abundant presence in natural phenomena and their diverse applications. However, the optical properties of CLC are usually hindered by the abundance of the so-called fingerprint domains. Up to now, studies have worked on controlling the in-plane orientation of the lying helix through surface rubbing and external stimuli. It remains challenging to achieve a steady and uniform lying helical structure. Here, by varying the surface anchoring strength, a uniform lying helical structure with long-range order is achieved as thermodynamically stable state without any external support. Poly (6-(4-methoxy-azobenzene-4’-oxy) hexyl methacrylate) (PMMAZO)—a liquid crystalline polymer—is deposited onto the silicon substrate to fine-tune the surface anchoring. By changing the grafting density of PMMAZO, both pitch size and morphology of the lying helical structure can be controlled. As the grafting density increases, the enhanced titled deformation of helical structure suppresses the pitch size of CLC at the same cell thickness; as the cell thickness increases, the morphology transition from long-range order stripes to small fingerprint domains is facilitated.

2019 ◽  
Vol 64 (4) ◽  
pp. 293 ◽  
Author(s):  
A. Iljin ◽  
D. Wei ◽  
U. Bortolozzo ◽  
S. Residori

The dynamic grating recording in dye-doped chiral nematic liquid crystals is studied. It is shown that the mechanism responsible for the grating recording can be ascribed to a photoinduced modification of the order parameter of a liquid crystal within the range of optical intensities, for which the orientational nonlinearity remains quenched by the structural order of the chiral structure. The two-wave mixing dynamic behavior is analyzed for different intensities of the recording beams, by comparing the self-diffraction regime with the probe diffraction. This allows us to distinguish a particular mechanism of optical nonlinearity. The photo-induced modulation of the order parameter and the respective changes of medium’s refractive indices determine the relatively fast response times, local nonlinear response, and quite high diffraction efficiency within an extremely wide intensity range (more than three orders of magnitude) The chiral helical structure hinders the nematic director reorientation, prevents the appearance of surface effects, and is very favorable for the manipulation of a nonlinear polarization. Such new mechanism could also be extended to the recording of arbitrary phase profiles as requested in several applications for the manipulation of a light-beam.


1995 ◽  
Vol 50 (11) ◽  
pp. 991-994 ◽  
Author(s):  
A. Kilian ◽  
A. Sonnet

Abstract A twist tensor (T-tensor) is introduced, which is defined for differentiable vector and director fields. Its eigensystem describes the local helical structure of the underlying field. It can have up to two nonzero eigenvalues, which indicate whether the local structure is untwisted, helical or double-twisted. The eigenvalues qi, if real valued, are the helical wave numbers, and the corresponding eigenvectors represent the local twist axes. The T-tensor can serve as a tool to analyze director configurations in chiral nematic liquid crystals, and applications in computational fluid dynamics seem feasible.


Author(s):  
Xuefeng Yang ◽  
Xue Jin ◽  
Tonghan Zhao ◽  
Pengfei Duan

Chiral nematic liquid crystals exhibit excellent performance in obtaining high luminescence dissymmetry factor of circularly polarized luminescence.


2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Dawei Zhang ◽  
Lihong Zhang ◽  
Bingzhe Wang ◽  
Guangzhe Piao

Stable lyotropic chiral nematic liquid crystals (N*-LCs) of cellulose nanocrystals (CNs) were prepared via hydrolysis using sulfuric acid. The lyotropic N*-LCs were used as an asymmetric reaction field to synthesize polyaniline (PANI) onto CNs by in situ polymerization. As a primary step, we examined the mesophase transition of the N*-LCs of CNs suspension before and after in situ polymerization of aniline (ANI) by polarizing optical microscopy. The structure of nanocomposites of PANI/CNs was investigated at a microscopic level using Fourier transform infrared spectroscopy and X-ray diffraction. Influence of the CNs-to-ANI ratio on the morphology of the nanocomposites was also investigated at macroscopic level by scanning electron and transmission electron microscopies. It is found that the weight ratio of CNs to aniline in the suspension significantly influenced the size of the PANI particles and interaction between CNs and PANI. Moreover, electrical properties of the obtained PANI/CNs films were studied using standard four-probe technique. It is expected that the lyotropic N*-LCs of CNs might be available for an asymmetric reaction field to produce novel composites of conjugated materials.


2014 ◽  
Vol 23 (04) ◽  
pp. 1450042 ◽  
Author(s):  
Michał Kwaśny ◽  
Urszula A. Laudyn ◽  
Katarzyna A. Rutkowska ◽  
Mirosław A. Karpierz

In this work, we study nematicons propagation at the disclination lines in a wedge-shaped planarly oriented sample. Using optimal beam parameters for light self-trapping and varying the input beam position and direction of the wave vector k with respect to the z-axis, we gain insight in the nematicons propagation in the highly disturbed area around two different types of disclination lines in chiral nematic.


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