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12 pages, 3471 KiB

Open AccessArticle

Thermal Conductivity and Orientation Structure of Liquid Crystalline Epoxy Thermosets Prepared by Latent Curing Catalyst

by Miyuki Harada and Takuya Matsumoto

Crystals 2024, 14(1), 47; https://doi.org/10.3390/cryst14010047 - 28 Dec 2023

Viewed by 988

Abstract

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a [...] Read more.

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a diglycidyl ether of 1-methyl-3-(4-phenylcyclohex-1-enyl)benzene was successfully synthesized as an LC epoxy and the LC temperature range was evaluated via differential scanning calorimeter (DSC). The synthesized LC epoxy was cured with m-phenylenediamine (m-PDA) as an amine-type curing agent and 1-(2-cyanoethyl)-2-undecylimidazole (CEUI) as a latent curing catalyst, respectively. The LC phase structure and domain size of the resultant epoxy thermosets were analyzed through X-ray diffraction (XRD) and polarized optical microscopy (POM). High thermal conductivity was observed in the m-PDA system (0.31 W/(m·K)) compared to the CEUI system (0.27 W/(m·K)). On the other hand, in composites loaded with 55 vol% Al₂O₃ particles as a thermal conductive filler, the CEUI composites showed a higher thermal conductivity value of 2.47 W/(m·K) than the m-PDA composites (1.70 W/(m·K)). This difference was attributed to the LC orientation of the epoxy matrix, induced by the hydroxyl groups on the alumina surface and the latent curing reaction. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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9 pages, 2294 KiB

Open AccessArticle

Angular-Dependent Back-Reflection of Chiral-Nematic Liquid Crystal Microparticles as Multifunctional Optical Elements

by Tomoki Shigeyama, Kohsuke Matsumoto, Kyohei Hisano and Osamu Tsutsumi

Crystals 2023, 13(12), 1660; https://doi.org/10.3390/cryst13121660 - 03 Dec 2023

Viewed by 1166

Abstract

The development of multifunctional optical elements capable of controlling polarization, wavelength, and propagation direction is pivotal for the miniaturization of optical devices. However, designing the spatial distribution of the refractive index for the fabrication of such elements remains challenging. This study demonstrates the [...] Read more.

The development of multifunctional optical elements capable of controlling polarization, wavelength, and propagation direction is pivotal for the miniaturization of optical devices. However, designing the spatial distribution of the refractive index for the fabrication of such elements remains challenging. This study demonstrates the spectroscopic function of microparticles composed of chiral-nematic liquid crystals (N* LC), which inherently selectively reflect circularly polarized light. The measurement of the reflection spectra with fiber probes revealed angular-dependent back-reflection of the single layer of the N* LC particles. These results indicate that our N* LC microparticles possess multiple optical functions, enabling the separation of incident light polarization and wavelength within a single material. This suggests broad applications of N* LC particles as compact optical elements. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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15 pages, 2174 KiB

Open AccessArticle

Eliminating Ambiguities in Electrical Measurements of Advanced Liquid Crystal Materials

by Oleksandr V. Kovalchuk, Tetiana M. Kovalchuk and Yuriy Garbovskiy

Crystals 2023, 13(7), 1093; https://doi.org/10.3390/cryst13071093 - 13 Jul 2023

Viewed by 1486

Abstract

Existing and future display and non-display applications of thermotropic liquid crystals rely on the development of new mesogenic materials. Electrical measurements of such materials determine their suitability for a specific application. In the case of molecular liquid crystals, their direct current (DC) electrical [...] Read more.

Existing and future display and non-display applications of thermotropic liquid crystals rely on the development of new mesogenic materials. Electrical measurements of such materials determine their suitability for a specific application. In the case of molecular liquid crystals, their direct current (DC) electrical conductivity is caused by inorganic and/or organic ions typically present in small quantities even in highly purified materials. Important information about ions in liquid crystals can be obtained by measuring their DC electrical conductivity. Available experimental reports indicate that evaluation of the DC electrical conductivity of liquid crystals is a very non-trivial task as there are many ambiguities. In this paper, we discuss how to eliminate ambiguities in electrical measurements of liquid crystals by considering interactions between ions and substrates of a liquid crystal cell. In addition, we analyze factors affecting a proper evaluation of DC electrical conductivity of advanced multifunctional materials composed of liquid crystals and nanoparticles. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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18 pages, 66797 KiB

Open AccessArticle

Phase-Only Liquid-Crystal-on-Silicon Spatial-Light-Modulator Uniformity Measurement with Improved Classical Polarimetric Method

by Xinyue Zhang and Kun Li

Crystals 2023, 13(6), 958; https://doi.org/10.3390/cryst13060958 - 15 Jun 2023

Viewed by 1101

Abstract

The classical polarimetric method has been widely used in liquid crystal on silicon (LCoS) phase measurement with a simple optical setup. However, due to interference caused by LCoS cover glass reflections, the method lacks accuracy for phase uniformity measurements. This paper is aimed [...] Read more.

The classical polarimetric method has been widely used in liquid crystal on silicon (LCoS) phase measurement with a simple optical setup. However, due to interference caused by LCoS cover glass reflections, the method lacks accuracy for phase uniformity measurements. This paper is aimed at mathematically analyzing the errors caused by non-ideal glass reflections and proposing procedures to reduce or eliminate such errors. The measurement is discussed in three conditions, including the ideal condition with no reflections from the LCoS cover glass, the condition with only the front reflection from the cover glass, and the condition with only the back reflection from the cover glass. It is discovered that the backward reflection makes the largest contribution to the overall measurement error, and it is the main obstacle to high-quality measurements. Several procedures, including optical alignment, LC layer thickness measurement, and phase estimation method, are proposed, making the uniformity measurement more qualitative and consistent. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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9 pages, 6981 KiB

Open AccessArticle

Design of Tunable Liquid Crystal Lenses with a Parabolic Phase Profile

by Wenbin Feng, Zhiqiang Liu, Hao Liu and Mao Ye

Crystals 2023, 13(1), 8; https://doi.org/10.3390/cryst13010008 - 21 Dec 2022

Cited by 4 | Viewed by 1468

Abstract

An electrode pattern design generating a parabolic voltage distribution, in combination with usage of the linear response range of the liquid crystal (LC) material, has been recently proposed to obtain nearly ideal phase profiles for LC lenses. This technique features low driving voltages, [...] Read more.

An electrode pattern design generating a parabolic voltage distribution, in combination with usage of the linear response range of the liquid crystal (LC) material, has been recently proposed to obtain nearly ideal phase profiles for LC lenses. This technique features low driving voltages, simple structure, compact design, and the absence of high-resistivity (HR) layers. In this work, the universal design principle is discussed in detail, which is applicable not only to LC lens design, but also to other LC devices with any phase profile. Several electrode patterns are presented to form a parabolic voltage distribution. An equivalent electric circuit of the LC lens based on the design principle is developed, and the simulation results are given. In the experiments, an LC lens using the feasible parameters is prepared, and its high-quality performance is demonstrated. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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14 pages, 2519 KiB

Open AccessArticle

Synthesis, Mesomorphic Properties and Application of (R,S)-1-Methylpentyl 4′-Hydroxybiphenyl-4-carboxylate Derivatives

by Magdalena Urbańska and Mateusz Szala

Crystals 2022, 12(12), 1710; https://doi.org/10.3390/cryst12121710 - 25 Nov 2022

Cited by 4 | Viewed by 1021

Abstract

Thirteen new liquid crystalline racemic mixtures were synthesized and investigated. For these racemic mixtures, the phase sequences and their changes were determined by polarizing optical microscopy (POM). The phase transition temperatures and transition enthalpies were checked by differential scanning calorimetry (DSC). All new [...] Read more.

Thirteen new liquid crystalline racemic mixtures were synthesized and investigated. For these racemic mixtures, the phase sequences and their changes were determined by polarizing optical microscopy (POM). The phase transition temperatures and transition enthalpies were checked by differential scanning calorimetry (DSC). All new racemates have an anticlinic smectic C_A phase in a broad temperature range. Three highly tilted antiferroelectric mixtures were doped with six racemates at a concentration of 20% by weight. The helical pitch of the prepared mixtures was measured by the spectrophotometry method. All doped mixtures have a longer helical pitch than the base mixtures. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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17 pages, 6196 KiB

Open AccessEditor’s ChoiceArticle

End-of-Life Liquid Crystal Displays Recycling: Physico-Chemical Properties of Recovered Liquid Crystals

by Idriss Moundoungou, Zohra Bouberka, Guy-Joël Fossi Tabieguia, Ana Barrera, Yazid Derouiche, Frédéric Dubois, Philippe Supiot, Corinne Foissac and Ulrich Maschke

Crystals 2022, 12(11), 1672; https://doi.org/10.3390/cryst12111672 - 19 Nov 2022

Cited by 2 | Viewed by 3896

Abstract

This report focuses particularly on liquid crystals display (LCD) panels because they represent a significant amount of all WEEE collected. Technologies involving liquid crystals (LCs) have enjoyed considerable success since the 1970s in all fields of LC displays (LCDs). This currently provokes the [...] Read more.

This report focuses particularly on liquid crystals display (LCD) panels because they represent a significant amount of all WEEE collected. Technologies involving liquid crystals (LCs) have enjoyed considerable success since the 1970s in all fields of LC displays (LCDs). This currently provokes the problem of waste generated by such equipment. Based on current statistical data, the LC amount represents approximately 1.3 g for a 35-inch diameter LCD panel unit possessing a total weight of 15 kg. In France, a recent study revealed LCD waste to represent an average of 5.6 panels per household. This represents an important quantity of LCs, which are generally destroyed by incineration or washed out with detergents during the recycling processes of end-of-life (EOL) LCDs. Hence, the aim of this study is to show that it is possible to remove LC molecules from EOL-LCD panels with the goal of valorizing them in new sectors. EOL-LCD panels have undergone various stages of dismantling, chemical treatments and characterization. The first stage of manual dismantling enables the elimination of the remaining physical components of the panels to process LC molecules only, sandwiched between the two glass plates. Mechanical treatment by scraping allows us to obtain a concentrate of LCs. The results obtained from chemical and physical techniques show that these molecules retain the characteristics essential for their operation in the field of optical and electro-optical devices. As the use of LCD surfaces continues to rise significantly, the amounts and economic stakes are huge, fully justifying the development of an LC recovery process for used panels. Many potential uses have been identified for these LC molecules: in new flat LCD panels after purification of the LCs concentrate, in PDLC systems, as lubricants or in thermal applications. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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8 pages, 788 KiB

Open AccessArticle

Direct Ink Writing of Anisotropic Luminescent Materials

by Mattia Sabadin, Jeroen A. H. P. Sol and Michael G. Debije

Crystals 2022, 12(11), 1642; https://doi.org/10.3390/cryst12111642 - 16 Nov 2022

Cited by 1 | Viewed by 1416

Abstract

Luminescent solar concentrators are relatively inexpensive devices proposed to collect, convert, and redirect incident (sun)light for a variety of potential applications. In this work, dichroic dyes are embedded in a liquid crystal elastomer matrix and used as feedstock for direct ink writing. Direct [...] Read more.

Luminescent solar concentrators are relatively inexpensive devices proposed to collect, convert, and redirect incident (sun)light for a variety of potential applications. In this work, dichroic dyes are embedded in a liquid crystal elastomer matrix and used as feedstock for direct ink writing. Direct ink writing is a promising and versatile application technique for arbitrarily aligning the dichroic dyes over glass and poly(methyl methacrylate) lightguide surfaces. The resulting prints display anisotropic edge emissions, and suggest usage as striking visual objects, combining localized color and intensity variations when viewed through a polarizer. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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12 pages, 6026 KiB

Open AccessEditor’s ChoiceArticle

Anisotropic Surface Formation Based on Brush-Coated Nickel-Doped Yttrium Oxide Film for Enhanced Electro-Optical Characteristics in Liquid Crystal Systems

by Dong-Wook Lee, Da-Bin Yang, Dong-Hyun Kim, Jin-Young Oh, Yang Liu and Dae-Shik Seo

Crystals 2022, 12(11), 1554; https://doi.org/10.3390/cryst12111554 - 31 Oct 2022

Cited by 1 | Viewed by 1652

Abstract

This paper introduces anisotropic nickel yttrium oxide (NYO) film formed by the brush coating technique. X-ray photoelectron spectroscopy confirmed well-formed NYO film after the curing process, and the morphology of the surface was investigated using atomic force microscopy. The shear stress driven from [...] Read more.

This paper introduces anisotropic nickel yttrium oxide (NYO) film formed by the brush coating technique. X-ray photoelectron spectroscopy confirmed well-formed NYO film after the curing process, and the morphology of the surface was investigated using atomic force microscopy. The shear stress driven from brush hair movements caused the nano/micro-grooved anisotropic surface structure of NYO. This anisotropic surface induced uniform liquid crystal (LC) alignment on the surface, which was confirmed by pre-tilt angle analysis and polarized optical microscopy. The contact angle measurements revealed an increase in hydrophilicity at higher temperature curing, which contributed to homogenous LC alignment. The NYO film achieved good optical transmittance and thermal stability as an LC alignment layer. In addition, the film demonstrated good electro-optical properties, stable switching, and significantly enhanced operating voltage performance in a twisted-nematic LC system. Therefore, we expect that this brush coating method can be applied to various inorganic materials to achieve an advanced LC alignment layer. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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Review

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11 pages, 2141 KiB

Open AccessReview

Development and Prospect of Viewing Angle Switchable Liquid Crystal Devices

by Le Zhou and Sijie Liu

Crystals 2022, 12(10), 1347; https://doi.org/10.3390/cryst12101347 - 24 Sep 2022

Cited by 12 | Viewed by 2669

Abstract

As we move from the industrial age to the information age, nowadays, the opportunity to access personal information in public increases as personal computers (PCs), cell phones, automated teller machines (ATM) and other portable display devices have come into wider use, so it [...] Read more.

As we move from the industrial age to the information age, nowadays, the opportunity to access personal information in public increases as personal computers (PCs), cell phones, automated teller machines (ATM) and other portable display devices have come into wider use, so it is well suited for these liquid crystal displays (LCDs) to switch between wide viewing angle (WVA) (share mode) and narrow viewing angle (NVA) (privacy mode). In this review, we have summarized structures, principles and characteristics of several devices that show great potential application in controllable anti-peeping displays in the eyesight of materials consist of pure liquid crystals (LCs), polymer dispersed LCs (PDLCs), polymer stabilized LCs (PSLCs) or polymer network LCs (PNLCs) and non-LCs, which provides systematic information for next-generation viewing angle-controllable LCDs with lower operating voltage, higher transmittance and good viewing angle controllable characteristics. Because LCs/polymer composite films have the advantages of long life, low power consumption and energy saving, they are regarded as the mainstream technology of next-generation viewing angle controllable displays. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Optical Devices)

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