Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

Melnyk, Olha; Garbovskiy, Yuriy; Bueno-Baqués, D.; Glushchenko, Anatoliy

doi:10.3390/cryst9060314

Cited by 21 publications

(12 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Unless otherwise specified, we will be using the parameters appropriate for the commercially available MLC‐2048 (Merck Ltd), a dual‐frequency nematic LC, which is well studied in the literature. [ 42–44 ] The Frank elastic constants are K 11 = 12.4 pN and K 33 = 24.7 pN; [ 45 ] we take a pretilt angle of 0.04 rad and an anchoring strength of W = 2 × 10 −4 J m −2 . [ 12 ] We found the wavelength‐dependent refractive indices using the Cauchy coefficients: A e = 1.6950, B e = −0.0015 µm 2 , C e = 0.0035 µm 4 , A o = 1.5200, B o = −0.0212 µm 2 , and C o = 0.0044 µm 4 , with a biasing voltage frequency of 1 kHz.…”

Section: Resultsmentioning

confidence: 99%

Vertically Stacked Soliton‐Like Domain Walls in Nematic Liquid Crystals

Jones

Melnyk

Macêdo

et al. 2021

Advcd Theory and Sims

Self Cite

View full text Add to dashboard Cite

In the standard liquid crystal (LC) geometry, one generally finds a quasi‐parabolic director profile in the vertical direction, where the directors are aligned with an applied field in the center of the cell. In contrast, using a numerical energy minimization approach, we find that there are multiple metastable solutions where the director profile is oscillatory. At low voltages, we find small oscillations, which evolve into standard soliton‐like domain walls as the applied voltage is increased. We predict the thickness of the domain wall with a simple analytic model that gives a good comparison to our numerical calculations, in the standard domain wall regime. For dual‐frequency nematic LCs, the occurrence of this regime can be tuned by a change of the biasing frequency. Moreover, we investigate how domain walls can affect the optical properties of LC‐based devices. For instance, we find that the transmittance curve shifts to higher voltages as domain walls are introduced. This shift can be used to create an efficient tunable filter.

show abstract

Section: Resultsmentioning

confidence: 99%

Vertically Stacked Soliton‐Like Domain Walls in Nematic Liquid Crystals

Jones

Melnyk

Macêdo

et al. 2021

Advcd Theory and Sims

Self Cite

View full text Add to dashboard Cite

show abstract

“…Different solutions have been proposed to overcome this limitation, although none of them has been successfully implemented in mm-wave. For instance, by using dual frequency LCs, the LC molecules can be actively forced to rotate in both directions depending on the bias frequency, which allows controlling the relaxation times through the applied electric field [19]. Alternatively, polymer network LC (PNLC) mixtures achieve better time response, which is the focus of this work.…”

Section: Introductionmentioning

confidence: 99%

mm-Wave Metasurface Unit Cells Achieving Millisecond Response Through Polymer Network Liquid Crystals

Guirado¹,

Perez-Palomino²,

Cano-Garcia³

et al. 2022

IEEE Access

View full text Add to dashboard Cite

The slow response time of planar Liquid Crystal (LC)-based phase-shift metasurface and Reconfigurable Intelligent Surfaces (RIS) cells is addressed in this paper by introducing a polymer network LC (PNLC) mixture suitable at mm-wave bands. Since the conventional effective isotropic model used in optical cells for describing the PNLC is not suitable in RF, an effective anisotropic and uniaxial model for such mixture is provided and experimentally validated at 100 GHz for the first time. In order to compare the temporal performance and tunability of the PNLC, transmissive and reflective cells, containing conventional LC and PNLC, have been manufactured and measured at optical and mm-wave frequencies. The temporal responses of PNLC are also compared for both RF and optical cells, obtaining relevant differences between their improvement factors, which are also discussed. Specifically, a 50 fold response time improvement is attained in cells designed to work at 100 GHz, although at the expense of a 3X tunability reduction. The model, which is robust to varying angle of incidence and cell dimensions, has been experimentally validated by designing and manufacturing a PNLC reflectarray cell of a different geometry. The cell shows reconfigurability times of 210ms, representing a significant improvement with respect to state-of-the-art response time in mm-wave cells, which are in the order of several seconds.

show abstract

“…When a nematic material with positive dielectric anisotropy is placed in an electric field exceeding a certain threshold, its molecules tend to assume a homeotropic alignment (parallel to the direction of the electric field and perpendicular to the cell surface). If the dielectric anisotropy is negative, the dominant orientation of the molecules is perpendicular to the direction of the electric field [ 9 , 10 , 11 ]. A correlation between the dielectric anisotropy and the molecular structure was described in detail by the theory of Maier and Meier [ 9 , 10 , 12 ].…”

Section: Introductionmentioning

confidence: 99%

DFT Studies of Selected Epoxies with Mesogenic Units–Impact of Molecular Structure on Electro-Optical Response

Włodarska

Mossety‐Leszczak

2021

IJMS

View full text Add to dashboard Cite

Theoretical studies of molecular structure and electric charge distribution were carried out for three epoxy compounds with different mesogenic cores. The compounds exhibit a nematic phase and form polymer networks that are potential bases for various composites. Results were compared to analogous materials with non-polar chains. A customized process involving geometry optimization of a series of conformations was employed to greatly increase likelihood of reaching global energy minimum for each molecule. All computations used Density Functional Theory (DFT) electron correlation model with the B3LYP hybrid functional. Molecular structure calculations yielded several parameters, including the magnitude and direction of the dipole moment, polarizability (α), first hyperpolarizability (β), and highest-occupied/lowest-unoccupied molecular orbital (HOMO-LUMO) energies. These parameters can help predict electronic properties of the nematic phase and the polymer network and assess their predisposition for application in electrooptical devices. In particular, the magnitude and direction of the dipole moment determine molecular alignment of liquid crystal phases in electric field, which enables controlling molecular order also in cured networks. Theoretical results were supplemented with observations of the nematics and their behavior in electric field. It was demonstrated for the studied compounds that a change in aliphatic chain polarity helps preserve and reinforce perpendicular alignment of molecules induced by electric field.

show abstract

Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

Cited by 21 publications

References 26 publications

Vertically Stacked Soliton‐Like Domain Walls in Nematic Liquid Crystals

Vertically Stacked Soliton‐Like Domain Walls in Nematic Liquid Crystals

mm-Wave Metasurface Unit Cells Achieving Millisecond Response Through Polymer Network Liquid Crystals

DFT Studies of Selected Epoxies with Mesogenic Units–Impact of Molecular Structure on Electro-Optical Response

Contact Info

Product

Resources

About