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Liquid Crystals in China
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Liquid Crystals in China

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (20 October 2021) | Viewed by 72542

Special Issue Editors

Prof. Dr. Vladimir Chigrinov

E-Mail Website
Guest Editor
Department of Electronic, Computer Engineering, Hong Kong University of Science and Technology, Hong Kong, China
Interests: liquid crystals; electrooptics; displays; photonics; photoalignment; photopatterning
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Qi Guo

E-Mail Website
Guest Editor
School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China
Interests: photo-alignment for ferroelectric liquid crystals; fast-response devices based on ferroelectric liquid crystals; photo-aligned liquid crystals for polarization detection
Dr. Jiatong Sun

E-Mail Website
Guest Editor
College of Information Science and Technology, Donghua University, Shanghai 201620, China
Interests: flexible liquid crystals displays; photo-aligning technique for one dimensional materials and polarization applications; optically driving liquid crystals devices; polarization navigation
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Ying Ma

E-Mail
Guest Editor
School of Physical Science and Technology, Northwestern Polytechnical University, Xi’an 710129, China
Interests: photo-alignment technique for fast optical elements based on ferroelectric liquid crystals; fast switching field sequential color displays

Special Issue Information

Dear Colleagues,

A new Crystals section has been established in the open access journal Crystals. Due to the many advances in recent years, we are dedicating the first Special Issue of the Crystals section to the topic “Liquid Crystals in China”. The Special Issue will explore techniques and challenges for liquid crystal physics, liquid crystal optics, liquid crystal chemistry, liquid crystal photonics, liquid crystal materials and devices, photo-aligning techniques for liquid crystals, 3D display, as well as flexible liquid crystal displays. It is intended that both extant and novel methods will be covered, ranging from traditional techniques to methods involving non-traditional technologies. The goal is to facilitate the dissemination of information on methods and outcomes that will benefit the broader community involved in the control of liquid crystals.

Prof. Dr. Vladimir Chigrinov
Prof. Dr. Qi Guo
Prof. Dr. Jiatong Sun
Prof. Dr. Ying Ma
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Liquid crystal physics
  • Liquid crystal optics
  • Liquid crystal chemistry
  • Liquid crystal photonics
  • Liquid crystal materials and devices
  • Photo-aligning techniques for liquid crystals
  • 3D display
  • Flexible liquid crystal displays

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Published Papers (15 papers)

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10 pages, 2971 KiB  
Article
Ferroelectric Liquid Crystal Compound Lens Based on Pancharatnam–Berry Phase
by Ying Ma, Mingkui Yin, Yuhang Shan, Vladimir G. Chigrinov, Hoi-Sing Kwok and Jianlin Zhao
Crystals 2022, 12(2), 231; https://doi.org/10.3390/cryst12020231 - 8 Feb 2022
Viewed by 2388
Abstract
We report a ferroelectric liquid crystal (FLC) compound lens based on the Pancharatnam–Berry (PB) phase. The phase of the FLC compound lens is an integration of polarization grating and a PB lens. Thus, when light passes through an FLC compound lens, the output [...] Read more.
We report a ferroelectric liquid crystal (FLC) compound lens based on the Pancharatnam–Berry (PB) phase. The phase of the FLC compound lens is an integration of polarization grating and a PB lens. Thus, when light passes through an FLC compound lens, the output light’s polarization handedness will be changed accordingly. In this case, FLC compound lenses can function as concave/convex lenses with spatially separated output light and rapid transmittance tunability. The FLC compound lenses were fabricated using a single-step holographic exposure system, based on a spatial light modulator working as numerous phase retarders. Photosensitive azo-dye material was used as the aligning layer. The output light transmittance of the FLC compound lens can be operated at 150 μs. Our results achieve the potential applications on various displays and augmented reality. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) SD1 with (<b>b</b>) its formula, providing the alignment direction perpendicular to the exposure polarization of the incident light. (<b>c</b>) Structure of a DHFLC cell and the rotating directions of the FLC molecules with external electric field. (<b>d</b>) Birefringence mechanism of DHFLC.</p> Full article ">Figure 2
<p>(<b>a</b>) Experimental setup of the single-step holographic exposure system used for a photo-sensitive azo-dye material SD1. (<b>b</b>) Simulation result of grayscale image loaded onto the SLM.</p> Full article ">Figure 3
<p>(<b>a</b>) Refractive index and (<b>b</b>) birefringence with applied electric field.</p> Full article ">Figure 4
<p>Simulation results of DHFLC compound lens efficiency with applied electric field.</p> Full article ">Figure 5
<p>Simulation results of the light field and corresponding intensity distribution captured at different positions away from the compound FLC lens with right-handed circularly polarized input light.</p> Full article ">Figure 6
<p>Simulation results of the light field and corresponding intensity distribution captured at different positions away from the compound FLC lens with left-handed circularly polarized input light.</p> Full article ">Figure 7
<p>Illustration of experiment setups for optical performance of fabricated FLC lens.</p> Full article ">Figure 8
<p>(<b>a</b>) Experimental results of the light field captured at different positions away from the FLC compound lens with left-handed circularly polarized incident light (left), linearly polarized incident light (middle) and right-handed circularly polarized incident light (right). (<b>b</b>) Microscopic photograph of the fabricated FLC lens.</p> Full article ">
5 pages, 2424 KiB  
Article
A Method to Improve the Lifetime of Microcapsule Electrophoretic Display Modules
by Xidu Wang, Guoyuan Li, Xi Zeng, Yu Chen and Dianlu Hu
Crystals 2021, 11(10), 1259; https://doi.org/10.3390/cryst11101259 - 18 Oct 2021
Cited by 1 | Viewed by 2231
Abstract
Microcapsule electrophoretic display (MED) is a kind of display with the properties of reflectivity and low power consumption. It is widely used in electronic book readers, but some new applications have appeared in the Internet of Things (IoT) products. Long working time is [...] Read more.
Microcapsule electrophoretic display (MED) is a kind of display with the properties of reflectivity and low power consumption. It is widely used in electronic book readers, but some new applications have appeared in the Internet of Things (IoT) products. Long working time is required in IoT products because it is not easy to replace or install such displays. The main failure phenomenon is the mura that will appear after about 1 to 2 years of use. The root cause of the failure is analyzed, and the lifetime prediction models for MED are introduced. The high temperature and high humidity (HTHH) test is used to evaluate the protective effect of the packaging structure. The HTHH test result is reported for the new MED structure; it shows that the MED with the new structure involves a longer working time. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>This is a cross-section of microcapsule electrophoretic display.</p> Full article ">Figure 2
<p>The cross-section for electrophoretic display.</p> Full article ">Figure 3
<p>The samples before HTHH test.</p> Full article ">Figure 4
<p>There is mura after 15 days of HTHH testing.</p> Full article ">Figure 5
<p>The pathway of moisture invading.</p> Full article ">Figure 6
<p>New method for microcapsule electrophoretic display package: change the protective sheet to glass.</p> Full article ">
9 pages, 2360 KiB  
Article
Broadband Tunable Terahertz Beam Deflector Based on Liquid Crystals and Graphene
by Yanchun Shen, Jinlan Wang, Qiaolian Wang, Ximing Qiao, Yuye Wang and Degang Xu
Crystals 2021, 11(9), 1141; https://doi.org/10.3390/cryst11091141 - 18 Sep 2021
Cited by 3 | Viewed by 2754
Abstract
Terahertz (THz) technology has unique applications in, for example, wireless communication, biochemical characterization, and security inspection. However, high-efficiency, low-cost, and actively tunable THz modulators are still scarce. We propose a broadband tunable THz beam deflector based on liquid crystals (LCs). By a periodic [...] Read more.
Terahertz (THz) technology has unique applications in, for example, wireless communication, biochemical characterization, and security inspection. However, high-efficiency, low-cost, and actively tunable THz modulators are still scarce. We propose a broadband tunable THz beam deflector based on liquid crystals (LCs). By a periodic gradual distribution of the orientation of the LC in one direction, a frequency-independent geometric phase modulation is obtained. The LC device with this specific orientation distribution was obtained through ultraviolet polarization exposure. We have verified the broadband beam deflection in both the simulation and experiment. The device can achieve a good spin-coupled beam deflection effect in the 0.8–1.2 Thz band, and the average polarization conversion efficiency exceeds 70%. Moreover, because the electro-optical responsivity of LCs is excellent, graphene transparent electrode layers introduced on the upper and lower substrates enable the deflection modulation to be switched and dynamic tuning to be achieved. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Schematic of the beam deflector. (<b>b</b>) Required grating phase along the <span class="html-italic">x</span>-axis. (<b>c</b>) Phase distribution diagram of the designed grating. (<b>d</b>) Prepared LC sample under crossed polarizers and orientation distribution in the corresponding area.</p> Full article ">Figure 2
<p>Schematic of the sample preparation process.</p> Full article ">Figure 3
<p>THz far-field intensity distributions: (<b>a</b>,<b>b</b>) Simulation results in the <span class="html-italic">xz</span>-plane under (<b>a</b>) LCP and (<b>b</b>) RCP incidence. (<b>c</b>,<b>d</b>) Measured results in the <span class="html-italic">xz</span>-plane and <span class="html-italic">xy</span>-plane (<span class="html-italic">z</span> = 15 mm) under (<b>c</b>) LCP and (<b>d</b>) RCP incidence, (<b>e,f</b>) Simulation results in the xz-plane under (<b>e</b>) LCP and (<b>f</b>) RCP incidence. The white solid curves show the horizontal intensity distribution along the white dashed lines.</p> Full article ">Figure 4
<p>(<b>a</b>,<b>b</b>) Measured THz far-field intensity distribution in the <span class="html-italic">xz</span>-plane in the frequency range of 0.8–1.2 THz band under (<b>a</b>) LCP and (<b>b</b>) RCP incidence. (<b>c</b>,<b>d</b>) Dependence of (<b>c</b>) deflection angle and (<b>d</b>) polarization conversion efficiency with frequency.</p> Full article ">Figure 5
<p>The polarization conversion efficiency at different liquid crystal thicknesses.</p> Full article ">Figure 6
<p>Results obtained after a saturation voltage is applied: (<b>a</b>) switchable function of the device; (<b>b</b>,<b>c</b>) far-field intensity distributions in the <span class="html-italic">xy</span>-plane under (<b>b</b>) LCP and (<b>c</b>) RCP incidence. The white solid line shows the horizontal intensity distribution along the white dashed line.</p> Full article ">
10 pages, 3831 KiB  
Article
Multi-View 2D/3D Switchable Display with Cylindrical Liquid Crystal Lens Array
by Fan Chu, Di Wang, Chao Liu, Lei Li and Qiong-Hua Wang
Crystals 2021, 11(6), 715; https://doi.org/10.3390/cryst11060715 - 21 Jun 2021
Cited by 23 | Viewed by 4123
Abstract
We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) [...] Read more.
We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) electrode, and bottom periodic strip ITO electrodes. In the voltage-off state, the cylindrical LC lens array is equivalent to a transparent glass substrate and the viewers can see a clear 2D image. In the 3D mode, the cylindrical LC lens array can be used as a cylindrical lens array under a suitable operating voltage. As a result, the 2D and 3D images can be switched according to the state of the cylindrical LC lens array. The experimental result shows that the 2D/3D switchable display with the cylindrical LC lens array has a wider viewing angle, has no moiré pattern, and is much thinner compared to the other 2D/3D switchable display devices. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Structure of the 2D/3D switchable display based on the cylindrical LC lens array in the (<b>a</b>) 2D mode and (<b>b</b>) 3D mode and (<b>c</b>) stereogram of 3D mode.</p> Full article ">Figure 2
<p>Method of eliminating moiré pattern.</p> Full article ">Figure 3
<p>Simulated (<b>a</b>) refractive index distribution of the cylindrical LC lens array with different operating voltages and (<b>b</b>) voltage-dependent focal length of the cylindrical LC lens array.</p> Full article ">Figure 4
<p>Simulated (<b>a</b>) LC director distribution and (<b>b</b>) relative phase profiles for the extraordinary ray of the proposed cylindrical LC lens array.</p> Full article ">Figure 5
<p>(<b>a</b>) Acquisition principle of 3D scene and (<b>b</b>) acquired EIA.</p> Full article ">Figure 6
<p>Fabricated cylindrical LC lens array with size of (<b>a</b>) length 140 mm, (<b>b</b>) width 70 mm, and the focusing effect of the cylindrical LC lens array with (<b>c</b>) 0 V and (<b>d</b>) 5.4 V operating voltages.</p> Full article ">Figure 7
<p>Interference fringes of the cylindrical LC lens array with (<b>a</b>) 0 V, (<b>b</b>) 5.4 V, and (<b>c</b>) 8 V operating voltages.</p> Full article ">Figure 8
<p>(<b>a</b>) 2D image with the cylindrical LC lens array at voltage-off state and (<b>b</b>) 3D image with the cylindrical LC lens array at voltage-on state.</p> Full article ">Figure 9
<p>3D images captured at (<b>a</b>) −45°, (<b>b</b>) 0°, and (<b>c</b>) 45° viewing angles.</p> Full article ">Figure 10
<p>(<b>a</b>) Response time measurement platform and (<b>b</b>) response time of the cylindrical LC lens array.</p> Full article ">
10 pages, 5710 KiB  
Article
Template Effect of Multi-Phase Liquid Crystals
by Yao Gao, Tengfei Huang and Jiangang Lu
Crystals 2021, 11(6), 602; https://doi.org/10.3390/cryst11060602 - 27 May 2021
Cited by 5 | Viewed by 2743
Abstract
The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, [...] Read more.
The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, which includes the refilling CLC and intrinsic template BPLC or SPLC, can be fabricated. By refilling a CLC of different chiral pitch into a CLC template, a multi-pitch CLC that includes the refilling CLC and intrinsic CLC, can be fabricated. Twist structure LC devices with multi-phase and multi-pitch show great potential for applications in optical communication, displays, and LC lasing. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>The arrangements of LC molecules in (<b>a</b>) planar texture state CLC; (<b>b</b>) focal conic CLC; (<b>c</b>) BPLC; (<b>d</b>) SPLC.</p> Full article ">Figure 2
<p>POM images of the PS-CLC precursor with: (<b>a</b>) isotropic phase (65 °C); (<b>b</b>) cholesteric phase (30 °C).</p> Full article ">Figure 3
<p>POM images of the PS-BPLC precursor with: (<b>a</b>) isotropic phase (60 °C); (<b>b</b>) blue phase (54 °C); (<b>c</b>) cholesteric phase (45 °C).</p> Full article ">Figure 4
<p>POM images of the PS-SPLC precursor with: (<b>a</b>) isotropic phase (50 °C); (<b>b</b>) sphere phase (44 °C); (<b>c</b>) cholesteric phase (37 °C).</p> Full article ">Figure 5
<p>The surface morphology of (<b>a</b>) PS-CLC and (<b>b</b>) T-CLC.</p> Full article ">Figure 6
<p>The surface morphology of (<b>a</b>) PS-BPLC and (<b>b</b>) T-BPLC.</p> Full article ">Figure 7
<p>The surface morphology of (<b>a</b>) PS-SPLC and (<b>b</b>) T-SPLC.</p> Full article ">Figure 8
<p>Schematic diagram of the transmittance measure system.</p> Full article ">Figure 9
<p>The reflection spectra of (<b>a</b>) the PS-CLC and T-CLC; (<b>b</b>) PS-BPLC and T-BPLC; (<b>c</b>) PS-SPLC and T-SPLC.</p> Full article ">Figure 10
<p>The reflection spectra of CLC1, BPLC1, and SPLC1.</p> Full article ">Figure 11
<p>The reflection spectra of CLC2, BPLC2, and SPLC2.</p> Full article ">Figure 12
<p>The reflection spectra of (<b>a</b>) CLC1, T-CLC, and the CLC template after refilling CLC1; (<b>b</b>) BPLC1, T-CLC, and the CLC template after refilling BPLC1; (<b>c</b>) SPLC1, T-CLC, and the CLC template after refilling SPLC1.</p> Full article ">Figure 13
<p>The reflection spectra of (<b>a</b>) CLC1, T-BPLC, and the BPLC template after refilling CLC1; (<b>b</b>) BPLC1, T-BPLC, and the BPLC template after refilling BPLC1; (<b>c</b>) SPLC1, T-BPLC, and the BPLC template after refilling SPLC1.</p> Full article ">Figure 14
<p>The reflection spectra of (<b>a</b>) CLC2, T-SPLC, and the SPLC template after refilling CLC2; (<b>b</b>) CLC2, T-SPLC, and the CLC2 were directly refilled into the SPLC template at 30 °C; (<b>c</b>) BPLC2, T-SPLC, and the SPLC template after refilling BPLC2; (<b>d</b>) SPLC2, T-SPLC, and the SPLC template after refilling SPLC2.</p> Full article ">
7 pages, 1723 KiB  
Article
Electrically Tunable Terahertz Focusing Modulator Enabled by Liquid Crystal Integrated Dielectric Metasurface
by Yanchun Shen, Zhixiong Shen, Yuye Wang, Degang Xu and Wei Hu
Crystals 2021, 11(5), 514; https://doi.org/10.3390/cryst11050514 - 6 May 2021
Cited by 9 | Viewed by 3064
Abstract
Active lenses with focal tunable properties are highly desired in the modern imaging systems from the visible to the microwaves. In this paper, we demonstrate a terahertz (THz) lens with electrically switchable focal length. It is composed of a large-birefringence liquid crystal (LC) [...] Read more.
Active lenses with focal tunable properties are highly desired in the modern imaging systems from the visible to the microwaves. In this paper, we demonstrate a terahertz (THz) lens with electrically switchable focal length. It is composed of a large-birefringence liquid crystal (LC) layer infiltrating a dielectric metasurface. When the birefringence of LC is tuned with an external bias, the phase shift of a single meta-unit will change. With parameter sweep using the finite-different time-domain (FDTD) simulation method, meta-units with varying geometries are optimized to achieve a focal length switchable metalens. The numerical results show that the focal length can be switched between 8.3 mm and 10.5 mm at bias OFF and ON states, respectively, which is consistent with the design. A feasible fabrication procedure of the lens is further discussed. Such a device can be designed beyond the THz band to the visible or the microwaves, and may be widely applied in integrated imaging systems. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>,<b>b</b>) Decomposed diagram of the liquid crystal integrated metalens at (<b>a</b>) bias OFF and (<b>b</b>) bias ON states, respectively. (<b>c</b>) Schematic of the meta-unit where the unit dimension is shown: periodicity, <span class="html-italic">P</span>: 130 μm; height of the silicon pilar, <span class="html-italic">h</span>: 235 μm; length of the pilar, <span class="html-italic">l</span>: 120 μm; width of the pilar, <span class="html-italic">w</span>: 40 μm; height of the LC layer, <span class="html-italic">H</span>: 250 μm. (<b>d</b>) Frequency-dependent phase shift when the <span class="html-italic">x</span>-polarized wave transmits through the meta-unit with the dimension shown in (<b>c</b>) at bias OFF (red line) and ON (blue line) states.</p> Full article ">Figure 2
<p>(<b>a</b>,<b>b</b>) Dependency of the phase shift on <span class="html-italic">l</span> and <span class="html-italic">w</span> when the <span class="html-italic">x</span>-polarized wave transmits through the meta-unit at (<b>a</b>) bias OFF and (<b>b</b>) bias ON states, respectively. (<b>c</b>,<b>d</b>) Dependency of the transmittance on <span class="html-italic">l</span> and <span class="html-italic">w</span> at (<b>c</b>) bias OFF and (<b>d</b>) bias ON states, respectively.</p> Full article ">Figure 3
<p>(<b>a</b>) Designed lens phase profiles with <span class="html-italic">f</span> = 8.3 mm (blue curve) and 10.5 mm (red curve) and phase shift of the meta-units with optimized dimensions along the radius at bias OFF (red dots) and bias ON (blue dots) states. (<b>b</b>) Optimized <span class="html-italic">l</span> (red dots) and <span class="html-italic">w</span> (blue dots) parameters of the meta-units along the radius.</p> Full article ">Figure 4
<p>(<b>a</b>,<b>b</b>) Simulated THz fields in the <span class="html-italic">xz</span>-plane at 1.0 THz at (<b>a</b>) bias OFF and (<b>b</b>) bias ON states, respectively. (<b>c</b>) Transverse intensity distributions at the focal planes labeled by the white dashed lines in (<b>a</b>) and (<b>b</b>) at bias OFF (red line) and bias ON (blue line) states.</p> Full article ">Figure 5
<p>A feasible fabrication procedure of the LC integrated metalens.</p> Full article ">
13 pages, 5531 KiB  
Article
High-Efficiency Responsive Smart Windows Fabricated by Carbon Nanotubes Modified by Liquid Crystalline Polymers
by Yuan Deng, Shi-Qin Li, Qian Yang, Zhi-Wang Luo and He-Lou Xie
Crystals 2021, 11(4), 440; https://doi.org/10.3390/cryst11040440 - 18 Apr 2021
Cited by 10 | Viewed by 3058
Abstract
Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) [...] Read more.
Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) response using carbon nanotubes grafted by biphenyl LC polymer brush (CNT-PDB) as the orientation layer. The resultant CNT-PDB polymer brush can provide the vertical orientation of LC molecules to maintain the initial transparency. At the same time, the smart window shows a rapid response to NIR light, which can quickly adjust the light transmittance to prevent sunlight from entering the room. Different from common doping systems, this method avoids the problem of poor compatibility between the LC host and photothermal conversion materials, which is beneficial for improving the durability of the device. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Dispersion image: A is CNT-COOH and B is CNT-PDB in chlorobenzene solution; (<b>b</b>) TEM image of CNT-PDB.</p> Full article ">Figure 2
<p>(<b>a</b>) The DSC curve of the polymer CNT-PDB. Inset image: POM image of the polymer CNT-PDB at 140 °C. (<b>b</b>) X-ray scattering profiles of the polymer CNT-PDB recorded at various temperatures upon heating and cooling.</p> Full article ">Figure 3
<p>POM photographs of PSLC alignment in CNT-PDB brush-coated hybrid cells at different spin-coating concentrations: (<b>a</b>) 2, (<b>b</b>) 1, (<b>c</b>) 0.5, (<b>d</b>) 0.1, (<b>e</b>) 0.05, and (<b>f</b>) 0.01 wt%.</p> Full article ">Figure 4
<p>The 3D topographic AFM image (<b>a</b>) and corresponding height profiles (<b>b</b>) of the 0.05 wt % of the CNT-PDB film on the silicon substrate.</p> Full article ">Figure 5
<p>Images of the proposed PSLC cells with different CNT-PDB polymer brush concentrations and their corresponding POM images. Upper right corner: transmittance value at 550 nm.</p> Full article ">Figure 6
<p>(<b>a</b>) IR images of the substrate coated with CNT-PDB polymer brush recorded at different NIR light irradiation times. (<b>b</b>) The maximum heating curves of polymer brushes with different concentrations under different NIR irradiation intensities. (<b>c</b>) The temperature of CNT-PDB polymer brush under cyclic NIR light radiation.</p> Full article ">Figure 7
<p>(<b>a</b>) The images of the fabricated PSLC cell in the SmA*, N*, and Iso phases. (<b>b</b>) Images of the fabricated PSLC cells with different polymer brush concentrations before and under NIR irradiation (27 °C, the incident height: 3 cm). Upper right corner: transmittance value at 550 nm after NIR irradiation.</p> Full article ">Figure 8
<p>(<b>a</b>) The relationship between response time and polymer brush concentration (<b>b</b>) The relationship between response time and NIR radiation intensity. (<b>c</b>) Maximum temperature rise of PSLC cells with different polymer brush concentrations under different light intensities.</p> Full article ">Scheme 1
<p>Chemical structure of CNT-PDB.</p> Full article ">Scheme 2
<p>(<b>a</b>) Chemical structures and contents of the compositions in ChLC mixtures; (<b>b</b>) the fabrication process of the PSLC cell.</p> Full article ">
8 pages, 21375 KiB  
Article
Light-Driven Pitch Tuning of Self-Assembled Hierarchical Gratings
by Yuan-Hang Wu, Sai-Bo Wu, Chao Liu, Qing-Gui Tan, Rui Yuan, Jing-Ge Wang, Ling-Ling Ma and Wei Hu
Crystals 2021, 11(4), 326; https://doi.org/10.3390/cryst11040326 - 25 Mar 2021
Cited by 3 | Viewed by 2682
Abstract
Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning [...] Read more.
Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning is accomplished in hierarchical gratings formed in a molecular switch doped CLC. We fabricate a checkerboard hierarchical CLC grating for a demonstration, whose pitch is optically tuned from 4.6 µm to 10.7 µm. Correspondingly, the first-order diffraction angle continuously changes from 9.4° to 4.8° and a significant polarization selectivity is also observed. In addition, hierarchical CLC gratings with triangular wave pattern, Archimedean spiral, and radial stripes are also demonstrated. This work creates new opportunities for soft-matter-based intelligent functional materials and advanced photonic devices. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Homogeneously aligned photo-responsive cholesteric liquid crystals (CLCs). (<b>a</b>,<b>c</b>) Schematic diagrams and (<b>b</b>,<b>d</b>) corresponding POM images of the planar texture and the electric field-induced grating. The chiral dopants, SD1 and LC molecules are marked by red, yellow and light blue rods, respectively. White arrows denote the transmission axes of polarizer and analyzer. The scale bar is 50 μm.</p> Full article ">Figure 2
<p>Optical tuning of the checkerboard hierarchical grating. (<b>a</b>) POM texture of checkerboard hierarchical grating obtained at 2.3 V, <span class="html-italic">f</span> = 1 kHz. Yellow arrows indicate local alignment directions; (<b>b</b>) optical tuning process of the grating under UV exposure. The exposure time is labeled; (<b>c</b>) dependency of <span class="html-italic">L</span> on <span class="html-italic">T</span>. White arrows denote the transmission axes of polarizer and analyzer. The scale bars are 50 μm.</p> Full article ">Figure 3
<p>Diffraction performance of checkerboard hierarchical gratings. (<b>a</b>) Schematic diagram of the light path. P and QWP represent the polarizer and the quarter wave plate, respectively. P1 and QWP are utilized to produce circularly polarized light. P2 is used to generate linearly polarized light; (<b>b</b>) diffraction pattern from the checkerboard hierarchical gratings; (<b>c</b>) optical tuning of the diffraction orders at <span class="html-italic">T</span> = 0 min, 5 min, 10 min, and 20 min, respectively; (<b>d</b>) polarization-dependent diffraction pattern. Circular and white arrows denote the polarization state of incident light.</p> Full article ">Figure 4
<p>Photopatterned CLC gratings. (<b>a</b>,<b>c</b>,<b>e</b>) Schematic diagrams of binary, radial and angular alignments; (<b>b</b>,<b>d</b>,<b>f</b>) corresponding images of fingerprint textures. SD1 molecules are represented by yellow bars. White arrows denote the polarizer transmission axes. All scale bars indicate 50 μm.</p> Full article ">
10 pages, 4873 KiB  
Article
Fast Tunable Biological Fluorescence Detection Device with Integrable Liquid Crystal Filter
by Qing Yang, Tong Sun, Xinyu Wu, Guangchao Cui, Mengzheng Yang, Zhongyang Bai, Lin Wang, Helin Li, Wenjing Chen, Qunwen Leng, Robert Puers, Ceyssens Frederik, Michael Kraft, Qinglin Song, Huabin Fang, Dewen Tian, Dexin Wang, Huijie Zhao, Weisheng Zhao, Tianxiao Nie, Qi Guo and Lianggong Wenadd Show full author list remove Hide full author list
Crystals 2021, 11(3), 272; https://doi.org/10.3390/cryst11030272 - 10 Mar 2021
Cited by 2 | Viewed by 2539
Abstract
Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid [...] Read more.
Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid crystal tunable filter (LCTF), in order to identify typical biological samples such as cells and bacteria. Hela cells labeled with red and green fluorescent proteins and Pseudomonas with fluorescence wavelengths of 610 nm, 509 nm and 450 nm, respectively, are inspected. High-resolution (6 μm) biofluorescent results have been achieved, together with clear images of the Hela cell clusters and the Pseudomonas bacteria colonies. Biofluorescence signals can be detected at a high transmittance (above 80%), and the response time of the device can reach 20 ms or below. The proposed method has the potential to be integrated into a microfluidic system to detect and identify the biofluorescent signals as a high throughput, low-cost option, for both high resolution and large field observation applications. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>(<b>a</b>) Fast tunable biofluorescence detection system with integrable liquid crystal filter (LCTF); Red fluorescent protein labeled Hela cells (RFP); Green fluorescent protein labeled Hela cells (GFP); (<b>b</b>) Experimental System setups; (<b>c</b>) Cell excitation light through designed LCTF; (<b>d</b>) UV excitation light and Pseudomonas fluorescent light.</p> Full article ">Figure 2
<p>(<b>a</b>) Experimental setup for spectrum filtering based on electrically controlled birefringence; (<b>b</b>) Corresponding optical path physical map.</p> Full article ">Figure 3
<p>(<b>a</b>) Schematic diagram of electrically controlled distribution of molecular directors and corresponding textures under polarized microscope; (<b>b</b>) The fluorescence transmittances versus applied voltages for the three wavelengths; (<b>c</b>) The curve of the maximum transmittance at different wavelengths.</p> Full article ">Figure 4
<p>Static characterization of the cells and Pseudomonas with scanning electron microscope (SEM) and fluorescent microscopic photographs.</p> Full article ">Figure 5
<p>(<b>a</b>) The relationship between the transmission of liquid crystal at different wavelengths and the signal frequency at both ends of the liquid crystal at a specific voltage; (<b>b</b>) Experimental confirmation of the speed of liquid crystal reaction.</p> Full article ">

Review

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19 pages, 3275 KiB  
Review
Mini-LED Backlight Technology Progress for Liquid Crystal Display
by Zhiwen Gao, Honglong Ning, Rihui Yao, Wei Xu, Wenxin Zou, Chenxiao Guo, Dongxiang Luo, Hengrong Xu and Junlin Xiao
Crystals 2022, 12(3), 313; https://doi.org/10.3390/cryst12030313 - 23 Feb 2022
Cited by 35 | Viewed by 10356
Abstract
As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to [...] Read more.
As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to greatly improve the contrast, color gamut, dark state and other element of the display performance of LCD displays. Mini-LED backlight technology is undoubtedly the most ideal solution to realize a highly dynamic range display of LCD displays, and has been widely commercialized in many fields such as TVs, tablet computers, notebook computers, and car monitors. This review mainly introduces the efforts made by researchers to eliminate the halo effect, thinning of the backlight module and reducing the backlight power consumption. The application of quantum dot technology in backlight is also presented. We predict that the number of Mini-LED backlight partitions is expected to reach a level of more than 3000 in the future, further utilizing the advantages of the small size in local dimming, but it will also inevitably be challenged by some issues such as power consumption and heat dissipation. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>Halo effect caused by mini-LED backlight [<a href="#B12-crystals-12-00313" class="html-bibr">12</a>].</p> Full article ">Figure 2
<p>The origin of the halo effect: halo1 is because the zone size is much larger than that of a pixel and halo2 is because of the light leakage from the bright zone to the adjacent dark zone [<a href="#B9-crystals-12-00313" class="html-bibr">9</a>].</p> Full article ">Figure 3
<p>Schematic diagram of LCD backlight unit: (<b>a</b>) Edge-lit backlight; (<b>b</b>) Direct-lit backlight.</p> Full article ">Figure 4
<p>Displayed image simulation:(<b>A</b>) Mini-LED backlight modulation; (<b>B</b>) Luminance distribution of the light incident on LC layer, and (<b>C</b>) Displayed image after LCD modulation [<a href="#B25-crystals-12-00313" class="html-bibr">25</a>].</p> Full article ">Figure 5
<p>Simulated LabPSNR for different HDR display systems with various local dimming zone numbers and LC contrast ratios [<a href="#B25-crystals-12-00313" class="html-bibr">25</a>].</p> Full article ">Figure 6
<p>Conceptual diagram of scaling up display size based on same angular size [<a href="#B25-crystals-12-00313" class="html-bibr">25</a>].</p> Full article ">Figure 7
<p>Difference in structure (<b>a</b>) without and (<b>b</b>)with slits [<a href="#B33-crystals-12-00313" class="html-bibr">33</a>].</p> Full article ">Figure 8
<p>Corner-lit backlight unit [<a href="#B21-crystals-12-00313" class="html-bibr">21</a>].</p> Full article ">Figure 9
<p>Schematic map: (<b>a</b>) Hybrid backlight equipped with sub-LGPs as physical local dimming zones; (<b>b</b>) Single local dimming zone enabled by edge-lit mini-LEDs embedded in the U grooves of the sub-LGP; (<b>c</b>) Cross-sectional view along the diagonal of the sub-LGP [<a href="#B44-crystals-12-00313" class="html-bibr">44</a>].</p> Full article ">Figure 10
<p>Proposed mini-LED backlight structure with reflective dots (one segment) [<a href="#B33-crystals-12-00313" class="html-bibr">33</a>].</p> Full article ">Figure 11
<p>Structure of the 2T1C driving circuit.</p> Full article ">Figure 12
<p>Schematic of quantum dots backlight: (<b>a</b>) “On-Chip” structure, (<b>b</b>) “On-Surface” structure (<b>c</b>) “On-Edge” structure.</p> Full article ">
21 pages, 3799 KiB  
Review
Survey of Mura Defect Detection in Liquid Crystal Displays Based on Machine Vision
by Wuyi Ming, Shengfei Zhang, Xuewen Liu, Kun Liu, Jie Yuan, Zhuobin Xie, Peiyan Sun and Xudong Guo
Crystals 2021, 11(12), 1444; https://doi.org/10.3390/cryst11121444 - 24 Nov 2021
Cited by 18 | Viewed by 8557
Abstract
Liquid crystal display (LCD) is a display device based on liquid crystal electro-optic effect, and LCDs have gradually appeared and have become an indispensable part of people’s lives. In the development of LCD technology, the detection of Mura defects is a key concern [...] Read more.
Liquid crystal display (LCD) is a display device based on liquid crystal electro-optic effect, and LCDs have gradually appeared and have become an indispensable part of people’s lives. In the development of LCD technology, the detection of Mura defects is a key concern in the manufacturing process. The Mura defect is a kind of display defect with low contrast and an irregular shape. This study first explains the mechanism of Mura defects in the LCD manufacturing process and classifies typical Mura defects. Then, three main purposes for the defect detection of LCDs are compared, and the advantages and disadvantages are conducted. Following that, this research examines reviews the linked literature on image preprocessing, feature extraction, dimension reduction, and classifiers of Mura defects. Finally, the future development trend and research direction of Mura defect detection based on machine vision can be drawn by this study. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>Development process of liquid crystal display technology, from the earliest principle to the current universal application.</p> Full article ">Figure 2
<p>Statistical chart of global TFT-LCD demand in recent years.</p> Full article ">Figure 3
<p>Manufacturing process of TFT-LCD.</p> Full article ">Figure 4
<p>Diagram of TFT structure.</p> Full article ">Figure 5
<p>Schematic diagram of common Mura defects [<a href="#B3-crystals-11-01444" class="html-bibr">3</a>]. Reprinted with permission from ref. [<a href="#B3-crystals-11-01444" class="html-bibr">3</a>], Copyright 2017 Huazhong University of Science and Technology.</p> Full article ">Figure 6
<p>Flow chart of automatic optical inspection of TFT-LCD Mura defect [<a href="#B3-crystals-11-01444" class="html-bibr">3</a>]. Reprinted with permission from ref. [<a href="#B3-crystals-11-01444" class="html-bibr">3</a>], Copyright 2017 Huazhong University of Science and Technology.</p> Full article ">Figure 7
<p>Image brightness nonuniformity processing [<a href="#B30-crystals-11-01444" class="html-bibr">30</a>]. Reprinted with permission from ref. [<a href="#B30-crystals-11-01444" class="html-bibr">30</a>]. Copyright 2013 Precision Engineering.</p> Full article ">Figure 8
<p>Common feature extraction for Mura defects methods.</p> Full article ">Figure 9
<p>Comparative of linear dimension reduction and nonlinear dimension reduction.</p> Full article ">Figure 10
<p>Accuracy comparison between SVM and BP neural network.</p> Full article ">
10 pages, 2592 KiB  
Review
Optically Rewritable Liquid Crystal Displays: Characteristics and Performance
by Vladimir G. Chigrinov, Aleksey A. Kudreyko and Fedor V. Podgornov
Crystals 2021, 11(9), 1053; https://doi.org/10.3390/cryst11091053 - 1 Sep 2021
Cited by 5 | Viewed by 2846
Abstract
Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing [...] Read more.
Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing studies do not include sufficient analysis on how to achieve acceptable reflective characteristics within short exposure time. In order to achieve this goal, we have applied the rotational diffusion model. We find that the parameters of the diffusion model can be adjusted to get acceptable light-reflecting characteristics within 10 s of exposure. In comparison with the long-time exposure, the reflectance coefficient reduces by 24%. The route to material improvements for optimized e-paper device is discussed. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>Azimuthal anchoring energy of nematic LC versus the exposure energy.</p> Full article ">Figure 2
<p>Dependence of photoinduced phase retardation on the exposure time for various powers per unit area (<span class="html-italic">W</span>) of the irradiated UV-light. Solid lines indicate numerical solutions, which were obtained by using rotational diffusion model.</p> Full article ">Figure 3
<p>(Color online) (<b>a</b>) Schematic representation of twisted nematic liquid crystal cell. (<b>b</b>) Device structure of ORW e-paper.</p> Full article ">Figure 4
<p>(Color online) ORW e-paper: (<b>a</b>) regular (<b>top</b>) and with improved dark state (<b>bottom</b>); (<b>b</b>) reflection spectra of dark and bright states for 0% and 0.5% dyes.</p> Full article ">Figure 5
<p>(Color online) Dependence of azo-dye rotation time (or formation of 70° LC twist angle) on the exposure light intensity from the 440 nm mercury line.</p> Full article ">Figure 6
<p>(Color online) (<b>a</b>) Intensity pulses of the exposure radiation. (<b>b</b>) Evolution of the probability density functions for different modes of the exposure radiation with identical mean intensities.</p> Full article ">Figure 7
<p>Kinetics of the relative order parameter with 10 s mean reorientation time.</p> Full article ">Figure 8
<p>(Color online) Calculated performance of ORW e-paper. (<b>a</b>) Angular characteristics of the contrast ratio. Angular characteristics of the reflectance coefficient for (<b>b</b>) bright and (<b>c</b>) dark states.</p> Full article ">Figure 9
<p>(Color online) Reflectance spectrum of ORW e-paper for bright- and dark states. The insert: computer-generated image with the reflective coefficients of 0.3285 and 0.0426 for bright and dark states, respectively.</p> Full article ">
16 pages, 8742 KiB  
Review
A Review of Two-Dimensional Liquid Crystal Polarization Gratings
by Kai Zuo, Yue Shi and Dan Luo
Crystals 2021, 11(9), 1015; https://doi.org/10.3390/cryst11091015 - 25 Aug 2021
Cited by 10 | Viewed by 4705
Abstract
In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal [...] Read more.
In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal manipulation stimulates the development of multibeam optical devices. Therefore, the development of two-dimensional (2D) PGs is in demand. This review summarizes the research progress of 2D PGs. Different designs and fabrication methods are summarized, including assembling two 1D polarization patterns, a 2D holographic lithography by polarization interference and a micro-pixelated electric field stimulated 2D liquid crystal (LC) structure. Both experiments and analyses are included. The design strategy, diffraction property, merits and demerits are discussed and summarized for the different methods. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>(<b>a</b>) Structure of the 2D LC PG by cross-assembling two 1D polarization patterns. (<b>b</b>) Diffraction patterns with different incident polarizations. Reproduced with permission from Reference [<a href="#B30-crystals-11-01015" class="html-bibr">30</a>] © The Optical Society.</p> Full article ">Figure 2
<p>(<b>a</b>) Structures of 2D LC PGs by assembling two 1D polarization patterns with crossing angle of π/2, 3π/4 and π, respectively. (<b>b</b>) Diffraction images of the corresponding structures from top to bottom with (left) LP, (middle) left CP (LCP) and right CP (RCP) incident beams. (<b>c</b>) The diffraction efficiency as a function of the applied ac voltage with a LCP probe beam for the sample with a π crossing angle. Reproduced from Reference [<a href="#B31-crystals-11-01015" class="html-bibr">31</a>] with permission from Taylor &amp; Francis.</p> Full article ">Figure 3
<p>(<b>a</b>) Simulated image of a 2D LC PG between crossed polarizers with a square web of disclinations. Diffraction pattern (<b>b</b>) and diffraction efficiency (<b>c</b>) with the applied ac voltage. (<b>d</b>) The square web of disclinations of LC observed by a polarized optical microscope (POM). (<b>e</b>) Schematic illustration of the square web of disclination lines in a LC cell. (<b>a</b>–<b>c</b>) Reproduced from Reference [<a href="#B32-crystals-11-01015" class="html-bibr">32</a>] with permission from AIP Publishing. (<b>d</b>,<b>e</b>) Reproduced from Reference [<a href="#B33-crystals-11-01015" class="html-bibr">33</a>] with permission from Springer Nature.</p> Full article ">Figure 4
<p>(<b>a</b>) LC texture observed by POM with LC director distribution illustrated for the top substrate (red on the left), bottom substrate (black on the left) and mid-plane (blue on the right) of a cell. (<b>b</b>) Simulated director profile of the cross-section for y = 0 (top) and y = Λ/2 (bottom) in the dimension of 2Λ*2Λ*d. (<b>c</b>) Measured diffraction intensity as a function of the ac voltage with RCP incident light. Inset: Diffraction pattern with 2-V applied voltage. (<b>d</b>) POM image of a 2D LC PG with different surface anchoring conditions with a half Λ/d ratio compared to the sample of (<b>a</b>–<b>c</b>): (A) strong anchoring on both substrates, (B) strong and weak anchoring on the bottom and top substrates, respectively, and (C) weak anchoring on both substrates. (<b>e</b>) Simulated diffraction pattern with unpolarized incident light for regions A, B and C2 of the sample (<b>d</b>). Reproduced from References [<a href="#B34-crystals-11-01015" class="html-bibr">34</a>,<a href="#B35-crystals-11-01015" class="html-bibr">35</a>] with permission from the Royal Society of Chemistry.</p> Full article ">Figure 5
<p>(<b>a</b>) Arrangement configuration of three interference beams. (<b>b</b>) Simulated intensity and polarization states of the interference field. (<b>c</b>) Simulated and (<b>d</b>) experimental observation of the LC texture by POM. (<b>e</b>) Experimental and (<b>f</b>) simulated diffraction pattern with RCP incident light. (<b>g</b>) Polar plots of the light polarizations. Lines: Simulation results; Scattered dots: Experiment results. Reproduced from Reference [<a href="#B37-crystals-11-01015" class="html-bibr">37</a>] with permission from AIP Publishing.</p> Full article ">Figure 6
<p>(<b>a</b>) Simulated intensity and (<b>b</b>) polarization state of the interference field. Inset: Arrangement and polarization configurations of the four interference beams. (<b>c</b>) Cross-section view of the LC director distribution in the dimensions of Λ*Λ*d. (<b>d</b>) Experimental and (<b>e</b>) simulated LC texture observed by POM. (<b>f</b>) Simulated diffraction pattern for LP (top) and RCP incident light (bottom) and for different incident wavelengths (phase retardation). (<b>g</b>) Calculated diffraction efficiency as a function of the phase retardation. (<b>h</b>) Polar plots of the light polarizations. Lines: Simulation results; Scattered dots: Experiment results. Reproduced from Reference [<a href="#B39-crystals-11-01015" class="html-bibr">39</a>] with permission from AIP Publishing.</p> Full article ">Figure 7
<p>(<b>a</b>) Simulated intensity and polarization profile of the interference field of four p-polarized beams. (<b>b</b>) Simulated LC orientation and (<b>c</b>) LC texture between the crossed polarizers. (<b>d</b>) LC texture observed by POM. (<b>e</b>) Diffraction intensity as a function of the applied ac voltage. Inset: Diffraction pattern. The diffraction intensity of each order varies with (<b>f</b>) linear and (<b>g</b>) elliptical incident polarization. Reproduced with permission from Reference [<a href="#B44-crystals-11-01015" class="html-bibr">44</a>] © The Optical Society.</p> Full article ">Figure 8
<p>(<b>a</b>) Arrangement and (<b>b</b>) polarization configurations of three interference beams: case i, case ii and case iii. (<b>c</b>) Simulated intensity and polarization states of the three cases. (<b>d</b>) Experimental diffraction patterns of the three cases. (<b>e</b>) Diffraction efficiency of spot A (open circles), B (filled circles) and C (open squares) as a function of azimuth polarization of the LP probing beam. Reproduced from Reference [<a href="#B45-crystals-11-01015" class="html-bibr">45</a>] with permission from AIP Publishing.</p> Full article ">Figure 9
<p>(<b>a</b>) 2D polarization pattern of four interference beams with orthogonal linear polarization. Inset: Arrangement and polarization configurations of the interference beams. (<b>b</b>) Calculated and (<b>c</b>) experimental diffraction patterns for the 2D PG. (<b>d</b>) 2D polarization pattern and (<b>e</b>) calculated and (<b>f</b>) experimental diffraction patterns for the 2D PG based on four interference beams with circular polarization. Reproduced with permission from Reference [<a href="#B46-crystals-11-01015" class="html-bibr">46</a>] © The Optical Society.</p> Full article ">Figure 10
<p>(<b>a</b>) Arrangement of the four interference beams. (<b>b</b>) Simulated intensity and (<b>c</b>) polarization states of the interference field. (<b>d</b>,<b>e</b>) Simulated LC texture and LC orientation between the crossed polarizers. (<b>f</b>) POM observation of the LC texture of the fabricated 2D PG. (<b>g</b>) The diffraction pattern varies with the input polarizations. (<b>h</b>) The diffraction efficiency as a function of relative phase retardation (Lines: Simulation result; Dots: Experiment result). (<b>i</b>) Polarization state of the diffraction pattern. (<b>j</b>) Polar plot of the polarization measurement of the 1st-order diffractions. Reproduced with permission from Reference [<a href="#B49-crystals-11-01015" class="html-bibr">49</a>] © The Optical Society.</p> Full article ">Figure 11
<p>(<b>a</b>) Arrangement of three interference beams. (<b>b</b>) Simulated polarization pattern of the interference field. (<b>c</b>) LC texture observed by POM. (<b>d</b>) Arrangement of the interference by introducing a LP beam. (<b>e</b>) Simulated polarization pattern of the interference field when the LP light intensity is 1/5 of each CP light (valid throughout the figure). (<b>f</b>) LC texture of the fabricated 2D PG observed by POM. (<b>g</b>) Simulated diffraction pattern at the half-wave conditions. (<b>h</b>) Diffraction pattern of the 2D LC PG from the experiment. (<b>i</b>) Diffraction efficiency as a function of LC phase retardation. Lines: Simulation results; Scattered dots: Experiment results. (<b>j</b>) Polarization selectivity of the 2D LC PG diffraction based on the simulation. (<b>k</b>) Polar plot of the polarization measurements of the 1st-order diffractions. Reproduced with permission from Reference [<a href="#B53-crystals-11-01015" class="html-bibr">53</a>] © The Optical Society.</p> Full article ">Figure 12
<p>(<b>a</b>) Schematic illustration of the LC sample with a micro-pixelated electric field. (<b>b</b>) The LC texture observed by POM with an illustration of the 2D LC director orientations. (<b>c</b>) The diffraction pattern of a CP incident beam with an applied 25-V 18.5 HZ ac voltage. The diffraction order is labeled based on the primitive cell vector of (<b>d</b>). (<b>d</b>) LC director orientation of unevenly tilted LC with umbilical defects. The normalized intensity of each diffraction spot observed in the experiment as a function of (<b>e</b>) the frequency with a fixed voltage and (<b>f</b>) the analyzer angle with a CP incident light. Simulated diffraction intensity as a function of the analyzer angle with a CP incident light, where the LC is assumed to have (<b>g</b>) planar alignment, as shown in (<b>b</b>), and (<b>h</b>) unevenly tilted alignment, as shown in (<b>d</b>). (<b>a</b>,<b>c–g</b>) Reproduced from Reference [<a href="#B57-crystals-11-01015" class="html-bibr">57</a>] with permission from the Royal Society of Chemistry. (<b>b</b>) Reproduced with permission from Reference [<a href="#B56-crystals-11-01015" class="html-bibr">56</a>] Copyright (2018) by the American Physical Society.</p> Full article ">
17 pages, 30796 KiB  
Review
Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism
by Lulu Xue, Ying Pan, Shaohai Zhang, Yinjie Chen, Haifeng Yu, Yonggang Yang, Lixin Mo, Zhicheng Sun, Luhai Li and Huai Yang
Crystals 2021, 11(7), 840; https://doi.org/10.3390/cryst11070840 - 20 Jul 2021
Cited by 19 | Viewed by 8921
Abstract
The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, [...] Read more.
The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, inducing aggregation, and metal-enhancement, which make the materials ideal for application in fluorescence probes, light-emitting devices, molecular detection, etc. Herein, we review the recently reported progress in the development of various fluorescent azobenzenes and summarize the possible mechanism of their fluorescence emission. The potential applications of these materials are also discussed. Finally, in order to guide research in this field, the existing problems and future development prospects are discussed. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>Reversible photoisomerization of azobenzene in two states.</p> Full article ">Figure 2
<p>(<b>a</b>) The molecule structures of azobenzene derivatives <b>1</b> with different donor and acceptor substituents. (<b>b</b>) SEM images of <b>1</b> after UV irradiation for 300 min. (<b>c</b>) The fluorescence spectra of <b>1</b>. (<b>b</b>,<b>c</b>) were reproduced with permission from [<a href="#B50-crystals-11-00840" class="html-bibr">50</a>]. Copyright 2006 American Chemical Society.</p> Full article ">Figure 3
<p>The molecule structures of a series of steric hindrance azobenzene derivatives <b>2a</b>–<b>2j</b>.</p> Full article ">Figure 4
<p>(<b>a</b>) The molecule structures of a series of steric hindrance azobenzene derivatives <b>3</b>, <b>4</b>. (<b>b</b>) Changes in UV-vis absorption spectral changes of azobenzene (<b>3</b>) solution (8 × 10<sup>−5</sup> M). After UV irradiation to reach a <span class="html-italic">cis</span>-rich photostationary state, the solution was stored in the dark at 20 °C for thermal <span class="html-italic">cis</span>-to-<span class="html-italic">trans</span> isomerization. Inset: changes in normalized absorbances at λ<sub>max</sub> as a function of time for thermal <span class="html-italic">cis</span>-to-<span class="html-italic">trans</span> isomerization. (<b>c</b>) Fluorescence of UV-exposed <b>4</b> solutions upon excitation at 365 nm. (<b>b</b>) was reproduced with permission from [<a href="#B54-crystals-11-00840" class="html-bibr">54</a>]. Copyright 2009, Elsevier. (<b>c</b>) Reproduced with permission from [<a href="#B55-crystals-11-00840" class="html-bibr">55</a>]. Copyright 2010 The Royal Society of Chemistry.</p> Full article ">Figure 5
<p>Working mechanism of the PET fluorescent molecular probe.</p> Full article ">Figure 6
<p>(<b>a</b>) The molecular structure of <b>5</b> and <b>6</b>. (<b>b</b>) The corrected emission spectra of <b>5</b> as a function of irradiation time for forward E→Z process: (1) before irradiation; (2) irradiation for 5 min; (3) 15 min; (4) 30 min; (5) 45 min; (6) 60 min; (7) 75 min; (8) 115 min. (<b>b</b>) was reproduced with permission from [<a href="#B59-crystals-11-00840" class="html-bibr">59</a>]. Copyright 1998 The Royal Society of Chemistry.</p> Full article ">Figure 7
<p>(<b>a</b>) The molecular structure of phenylphenol azobenzene and its polymers (<b>b</b>,<b>c</b>) The fluorescence spectra of <b>7</b> and <b>8</b> upon UV irradiation after various time intervals (0 min, 30 min, 60 min, 90 min). (<b>b</b>) and (<b>c</b>) were reproduced with permission from [<a href="#B60-crystals-11-00840" class="html-bibr">60</a>]. Copyright 2007 American Chemical Society.</p> Full article ">Figure 8
<p>The molecular structure of azobenzene derivatives <b>9</b> and <b>10</b> which chelated with Zn<sup>2+</sup>.</p> Full article ">Figure 9
<p>The molecular structure of 1-methyl-1,2,3,4,5-pentaphenylsilole and pentacenequinone derivatives.</p> Full article ">Figure 10
<p>Molecular structure of azobenzene derivatives <b>11</b> and dendrimer azobenzene <b>12</b>.</p> Full article ">Figure 11
<p>(<b>a</b>) The molecular structure of AIE azobenzene molecules <b>13</b>, <b>14</b>, <b>15</b>. (<b>b</b>) Emission spectra of the 10TBMB (<b>15</b>) in H<sub>2</sub>O/THF mixtures with different water volume fractions (<span class="html-italic">f<sub>w</sub></span>, vol% volume fraction). (c) Changes in the fluorescence quantum yield (Φ<sub>F</sub>) of 10TBMB (<b>15</b>) in H<sub>2</sub>O/THF mixtures with <span class="html-italic">f<sub>w</sub></span>. (<b>b</b>,<b>c</b>) were reproduced with permission from [<a href="#B85-crystals-11-00840" class="html-bibr">85</a>]. Copyright 2018 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.</p> Full article ">Figure 12
<p>The molecular structure of azobenzene-containing polymers <b>16</b>, <b>17</b> and <b>18</b> with AIE properties.</p> Full article ">Figure 13
<p>The molecular structure of azobenzene-containing polymers <b>19</b>–<b>26</b>.</p> Full article ">Figure 14
<p>(<b>a</b>) The molecular structure of azobenzene-containing polymers <b>27</b>–<b>30</b>. (<b>b</b>) The change in fluorescence at 430 nm upon UV irradiation (365 nm, 70 mW/cm<sup>2</sup>). (<b>c</b>) The fluorescence emission spectra of <b>29</b> (5 mg/mL, λ<sub>ex</sub>=360 nm, slit:10 nm) at different pH values. (<b>d</b>) The change in fluorescence of <b>29</b> at different temperatures (λ<sub>ex</sub>=360 nm, slit 10 nm). (<b>b</b>–<b>d</b>) were reproduced with permission from [<a href="#B70-crystals-11-00840" class="html-bibr">70</a>]. Copyright 2016 Elsevier.</p> Full article ">Figure 15
<p>The molecular structure of azobenzene derivatives <b>30–33</b>.</p> Full article ">Figure 16
<p>The molecular structure of <b>34</b>.</p> Full article ">Figure 17
<p>(<b>a</b>) The molecular structure of azobenzene derivatives <b>35</b>. (<b>b</b>) Fluorescence spectra of <b>35</b> in ethonal (1 × 10<sup>−3</sup> M) under 365 nm irradiation for different times at room temperature. Inset: the image of <b>35</b> after (left) and before (right) UV irradiation. (<b>c</b>,<b>d</b>) SEM images of <b>35</b> in ethonal (1 × 10<sup>−3</sup> M) before exposure to UV light and under irradiation at 365 nm for 290 min, respectively. (<b>b</b>–<b>d</b>) were reproduced with permission from [<a href="#B92-crystals-11-00840" class="html-bibr">92</a>]. Copyright 2014 The Royal Society of Chemistry.</p> Full article ">Figure 18
<p>The molecular structure of azopyridine complex <b>36</b>.</p> Full article ">Figure 19
<p>The molecular structure of azobenzene compounds <b>37</b>–<b>43</b>.</p> Full article ">Figure 20
<p>The molecular structure of a series heteroatomic coordination azobenzene complexs <b>44</b>–<b>47</b>.</p> Full article ">
22 pages, 3293 KiB  
Review
Recent Developments in Flexible Transparent Electrode
by Tingting Wang, Kuankuan Lu, Zhuohui Xu, Zimian Lin, Honglong Ning, Tian Qiu, Zhao Yang, Hua Zheng, Rihui Yao and Junbiao Peng
Crystals 2021, 11(5), 511; https://doi.org/10.3390/cryst11050511 - 5 May 2021
Cited by 54 | Viewed by 9434
Abstract
With the rapid development of flexible electronic devices (especially flexible LCD/OLED), flexible transparent electrodes (FTEs) with high light transmittance, high electrical conductivity, and excellent stretchability have attracted extensive attention from researchers and businesses. FTEs serve as an important part of display devices (touch [...] Read more.
With the rapid development of flexible electronic devices (especially flexible LCD/OLED), flexible transparent electrodes (FTEs) with high light transmittance, high electrical conductivity, and excellent stretchability have attracted extensive attention from researchers and businesses. FTEs serve as an important part of display devices (touch screen and display), energy storage devices (solar cells and super capacitors), and wearable medical devices (electronic skin). In this paper, we review the recent progress in the field of FTEs, with special emphasis on metal materials, carbon-based materials, conductive polymers (CPs), and composite materials, which are good alternatives to the traditional commercial transparent electrode (i.e., indium tin oxide, ITO). With respect to production methods, this article provides a detailed discussion on the performance differences and practical applications of different materials. Furthermore, major challenges and future developments of FTEs are also discussed. Full article
(This article belongs to the Special Issue Liquid Crystals in China)
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<p>(<b>a</b>) SEM and (<b>b</b>) TEM images of AgNWs [<a href="#B20-crystals-11-00511" class="html-bibr">20</a>]; (<b>c</b>,<b>d</b>) SEM images of CuNWs at different magnifications [<a href="#B41-crystals-11-00511" class="html-bibr">41</a>]; (<b>e</b>) schematic diagram of AgNW synthesis process [<a href="#B20-crystals-11-00511" class="html-bibr">20</a>]; (<b>f</b>) schematic diagram of a healable nanocomposite conductor based on CuNWs and DA-PU [<a href="#B40-crystals-11-00511" class="html-bibr">40</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic sketch of metal film deposition (conventional deposition and new multilayer deposition strategy) [<a href="#B55-crystals-11-00511" class="html-bibr">55</a>]; (<b>b</b>) schematic structure of the ZnO/Ag/ZnO transparent heater fabricated on top of a transparent PI substrate [<a href="#B50-crystals-11-00511" class="html-bibr">50</a>]; (<b>c</b>) schematic architecture of a stretchable ACEL device before and after stretching; (<b>d</b>) photographs and OM images of patterned ACUF/anisotropic conductive ultrathin film (ACUF)/Au electrodes and their interconnection [<a href="#B11-crystals-11-00511" class="html-bibr">11</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Schematic illustration of the preparation of transparent and conductive Ag mesh films; (<b>b</b>,<b>d</b>) SEM images of Ag mesh films fabricated with Ag nanoparticle ink after a sintering process; (<b>c</b>,<b>e</b>) SEM images of Ag mesh films fabricated with Ag nanoparticle ink after a coupling process [<a href="#B68-crystals-11-00511" class="html-bibr">68</a>].</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic illustration of the preparation of copper meshes on a flexible substrate; (<b>b</b>) SEM image of copper nanoparticles; (<b>c</b>) evolution of sheet resistance and transparency at 550 nm wavelength with mesh size; (<b>d</b>) evolution of sheet resistance and transparency at 550 nm wavelength with line width; (<b>e</b>) sheet resistance variation (R/R<sub>0</sub>) versus the number of cycles of repeated bending to a radius of 3 mm [<a href="#B69-crystals-11-00511" class="html-bibr">69</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) TEM image of CNTs [<a href="#B73-crystals-11-00511" class="html-bibr">73</a>]; (<b>b</b>) representation of the layer-by-layer schematic process and multilayer transfer process [<a href="#B88-crystals-11-00511" class="html-bibr">88</a>].</p> Full article ">Figure 6
<p>The preparation processes of a Polydimethylsiloxane (PDMS) dielectric layer with micro-pyramid structures and pressure sensor-based graphene electrodes [<a href="#B96-crystals-11-00511" class="html-bibr">96</a>].</p> Full article ">Figure 7
<p>Schematic diagram of PVDF/DMAAm gel synthesis process using 3D gel printer [<a href="#B116-crystals-11-00511" class="html-bibr">116</a>].</p> Full article ">Figure 8
<p>Schematic representation of nanocomposite thin film production: (<b>a</b>) glass substrate; (<b>b</b>) spin-coated glass with conductive material; (<b>c</b>) polymeric material-coated conductive glass; (<b>d</b>) removal of conductive polymeric film from glass; (<b>e</b>) self-standing conductive polymeric layer [<a href="#B9-crystals-11-00511" class="html-bibr">9</a>].</p> Full article ">Figure 9
<p>Radar map of different material properties.</p> Full article ">Figure 10
<p>Concept of metal atomic layer deposition (ALD) on graphene. (<b>a</b>) Doping graphene by charge transfer between graphene and metal. (<b>b</b>) Selective deposition of Pt by ALD on graphene [<a href="#B123-crystals-11-00511" class="html-bibr">123</a>].</p> Full article ">Figure 11
<p>The applications of FTEs.</p> Full article ">
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