Exotic structures of a thin film of chiral liquid crystals: a numerical study based on the Landau–de Gennes theory

Fukuda, Jun Ichi

doi:10.1080/21680396.2022.2077256

Cited by 3 publications

(2 citation statements)

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“…For the calculation of the structures of our cholesteric blue phase cell, we make use of the Landau-de Gennes continuum theory in which the orientational order of the liquid crystal is represented by a second-rank symmetric and traceless tensor χ αβ . Details of the theory and the numerical calculation are presented in our previous papers (Fukuda et al, 2009;Fukuda and Žumer 2010a;2010b;Fukuda and Žumer 2011a;Nych et al, 2017;Fukuda and Žumer 2020;Fukuda 2022;Fukuda et al, 2022), and here we present their essence.…”

Section: Model Calculation Of Bp Structuresmentioning

confidence: 99%

“…In the present study η is set to one corresponding to the so-called one-constant approximation setting the splay, twist and bend Frank elastic constants to be equal. We have adopted this approximation just for simplicity, and in usual nematic liquid crystal made of rodlike molecules, twist elastic constant is smaller than the other two, and smaller twist elastic constant is realized by taking η > 1 (Wright and Mermin 1989;Fukuda 2022). Here and in the following, summations over repeated Greek indices are implied (Hence, in Eq.…”

Section: Model Calculation Of Bp Structuresmentioning

confidence: 99%

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Simulation of a cholesteric blue phase cell with large but finite thickness

Fukuda

2022

Front. Soft. Matter

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We investigate the structure of a cholesteric blue phase (BP) liquid crystal cell of finite thickness under an electric field normal to the planar surfaces confining the liquid crystal. We carry out large scale simulations to consider cases in which the thickness of the BP liquid crystal is approximately 40 times the BP lattice constant (typical thickness in experiments), larger than that of previous simulation studies. Our calculations clearly demonstrate that the number of periodic structures along the thickness direction (thickness divided by the lattice constant) is discretized by the presence of confining surfaces. The stability of the so-called BP X structure over the BP I under the electric field, as well as the electrostriction, is confirmed. The metastability of the BP X structure after the cessation of the electric field, demonstrated in a recent experiment [Nat. Mater. 19, 94 (2020)] is also shown. We also perform calculations for the reflection spectra of the BP structures, and clearly observe the shift of the reflection peak due to electrostriction. Our study demonstrates the role of finite thickness on the behavior of a BP cell.

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Section: Model Calculation Of Bp Structuresmentioning

confidence: 99%

Section: Model Calculation Of Bp Structuresmentioning

confidence: 99%

Simulation of a cholesteric blue phase cell with large but finite thickness

Fukuda

2022

Front. Soft. Matter

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Direct simulation and machine learning structure identification unravel soft martensitic transformation and twinning dynamics

Fukuda,

Takahashi

2024

Proc. Natl. Acad. Sci. U.S.A.

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Phase transition between ordered phases has garnered attention from the viewpoint of materials science as well as statistical physics. One interesting example is martensitic transformation and the resulting formation of twin structures, in which atoms or molecules that form one crystalline phase move in a concerted and diffusionless manner toward another crystalline phase. Recently martensitic transformation has been observed experimentally also in various soft materials. However, the complex internal structures involving many molecules have eluded direct investigation of the dynamical processes of martensitic transformation. Here, we carry out a direct simulation of mesoscale structural transition of a liquid crystalline blue phase (BP) of cubic symmetry, known as BP II. The dynamics is simulated by a Langevin-type equation for the orientational order parameter with thermal fluctuations. We demonstrate that machine-learning-aided analysis of local structures successfully unravels the transformation process from a perfect lattice of BP II to a twinned lattice of another BP (BP I). The nucleation of BP I is initiated by the breakup of junctions of line defects (disclinations), followed by the deformation of disclination network. We further show that twinned BP I is reversibly transformed to a perfect lattice of BP II by temperature variation. Order-parameter-based simulations with machine-learning-aided local structure identification provide valuable insights into not only the martensitic transformation of soft materials but also a wider class of complex structural transitions between ordered phases.

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