scholarly journals Smart Window with Active-Passive Hybrid Control

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4137
Author(s):  
Heng-Yi Tseng ◽  
Li-Min Chang ◽  
Kuan-Wu Lin ◽  
Cheng-Chang Li ◽  
Wan-Hsuan Lin ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Voltage Pulse ◽  
Hybrid Control ◽  
Cholesteric Liquid Crystal ◽  
Low Frequency ◽  
Operating Mode ◽  
Smart Window ◽  
Smart Windows ◽  
Dichroic Dye ◽  
Scattering State

Dimming and scattering control are two of the major features of smart windows, which provide adjustable sunlight intensity and protect the privacy of people in a building. A hybrid photo- and electrical-controllable smart window that exploits salt and photochromic dichroic dye-doped cholesteric liquid crystal was developed. The photochromic dichroic dye causes a change in transmittance from high to low upon exposure to sunlight. When the light source is removed, the smart window returns from colored to colorless. The salt-doped cholesteric liquid crystal can be bi-stably switched from transparent into the scattering state by a low-frequency voltage pulse and switched back to its transparent state by a high-frequency voltage pulse. In its operating mode, an LC smart window can be passively dimmed by sunlight and the haze can be actively controlled by applying an electrical field to it; it therefore exhibits four optical states—transparent, scattering, dark clear, and dark opaque. Each state is stable in the absence of an applied voltage. This smart window can automatically dim when the sunlight gets stronger, and according to user needs, actively adjust the haze to achieve privacy protection.

Luminescent dichroic-dye-doped cholesteric liquid-crystal displays

2004 ◽  
Vol 12 (3) ◽  
pp. 341 ◽  
Author(s):  
Andro Chanishvili ◽  
Guram Chilaya ◽  
Gia Petriashvili ◽  
Riccardo Barberi ◽  
Roberto Bartolino ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Liquid Crystal Displays ◽  
Dichroic Dye

scholarly journals Pitch Gradation by Ion-Dragging Effect in Polymer-Stabilized Cholesteric Liquid Crystal Reflector Device

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 96 ◽  
Author(s):  
Xiaowen Hu ◽  
Weijie Zeng ◽  
Xinmin Zhang ◽  
Kai Wang ◽  
Xiaoling Liao ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Ex Situ ◽  
Polymerization Process ◽  
Heat Radiation ◽  
Smart Window ◽  
Dc Bias ◽  
Polymer Stabilized ◽  
Bandwidth Broadening

An IR reflector based on polymer-stabilized cholesteric liquid crystal (PSCLC) can selectively tune IR light reflection for smart window application. Broadening the reflection bandwidth to block more IR heat radiation requires the expansion of the pitch distribution in the PSCLC. Traditional attempts using ex situ direct current (DC) bias upon an already polymerized PSCLC reflector usually require a sustaining potential difference holding the pitch gradient of the reflector. Removing the DC bias will lead to a reflect bandwidth comeback. Here, we have developed an in situ DC curing strategy to realize an irreversible reflect bandwidth broadening. Briefly, a DC bias was used to drive the redistribution of impurity cations, which can be captured by the ester group of oligomers, during the photopolymerization. During the slow polymerization process, such trapped cations will drag the oligomers towards the cathode and compress the pitch length near the cathode before the oligomers form the long polymer chain. Consequently, a frozen pitch gradient by such an in-situ-electric-field-assisted dynamic ion-dragging effect leads to the formation of a pitch gradient along the electrical field direction. After removing the DC bias, the as-cured polymer is observed to have frozen such a gradient pitch feature without recoverable change. As a result, the PSCLC reflector exhibits steady bandwidth broadening of 480 nm in the IR region, which provides the potential for saving energy as a smart window.

A cholesteric liquid crystal smart window with a low operating voltage

2022 ◽  
Vol 197 ◽  
pp. 109843
Author(s):  
Seung-Won Oh ◽  
Seong-Min Ji ◽  
Chan-Hee Han ◽  
Tae-Hoon Yoon
Keyword(s):  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Operating Voltage ◽  
Smart Window

scholarly journals Normally transparent smart window based on electrically induced instability in dielectrically negative cholesteric liquid crystal

2018 ◽  
Vol 8 (3) ◽  
pp. 691 ◽  
Author(s):  
Chun-Wei Chen ◽  
Alyssa N. Brigeman ◽  
Tsung-Jui Ho ◽  
Iam Choon Khoo
Keyword(s):  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Smart Window

scholarly journals Bistable Smart Window Based on Ionic Liquid Doped Cholesteric Liquid Crystal

2017 ◽  
Vol 9 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Zhaojue Lan ◽  
Yong Li ◽  
Haitao Dai ◽  
Dan Luo
Keyword(s):  
Ionic Liquid ◽  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Smart Window

scholarly journals Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell

Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 183 ◽  
Author(s):  
Chia-Hua Yu ◽  
Po-Chang Wu ◽  
Wei Lee
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Voltage Pulse ◽  
Cholesteric Liquid Crystal ◽  
Liquid Crystal Cell ◽  
Dielectric Anisotropy ◽  
Isotropic Phase ◽  
Dielectric Heating ◽  
Surface Pretreatment ◽  
Crystal Cell

We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f1 and, subsequently, f2, which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 Vrms at f1 = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 Vrms and f1 = 55 kHz, our results indicate that switching of the voltage frequency from f1 to f2 enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f2 = 1 kHz or by the electrohydrodynamic effect at f2 = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.

scholarly journals Dye-Doped Electrically Smart Windows Based on Polymer-Stabilized Liquid Crystal

Polymers ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 694 ◽  
Author(s):  
Haitao Sun ◽  
Zuoping Xie ◽  
Chun Ju ◽  
Xiaowen Hu ◽  
Dong Yuan ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Fast Response ◽  
Smart Windows ◽  
Visual Contrast ◽  
Dichroic Dye ◽  
Light Management ◽  
Dependent Absorption ◽  
Dye Doping ◽  
Polymer Stabilized ◽  
Doped Polymer

Here we report the fabrication of dye-doped polymer-stabilized liquid crystals (PSLC)-based smart windows. The effect of dye doping on PSLC contrast was investigated. Non-dichroic dye tints the PSLC sample in both off- and on-state, which is not beneficial for increasing its off/on contrast. The sample doped with dichroic dye shows a slight color in the off-state and strong color in the on-state, resulting in an enhanced contrast, which attributed to orientation dependent absorption of dichroic dyes. Furthermore, we blended non-dichroic dye and dichroic dye who have complementary absorption together into PSLC mixture. The sample is almost colorless in the off-state due to the subtractive process, while colored in the on-state. The contrast is further enhanced. The results show that the proposed multi-dye-doped PSLC device has high visual contrast and fast response time, making it attractive for applications in light management and architectural aesthetics.

scholarly journals Smart Window Based on Angular-Selective Absorption of Solar Radiation with Guest–Host Liquid Crystals

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 131
Author(s):  
Seong-Min Ji ◽  
Seung-Won Oh ◽  
Tae-Hoon Yoon
Keyword(s):  
Liquid Crystal ◽  
Energy Consumption ◽  
Liquid Crystals ◽  
Solar Radiation ◽  
Applied Voltage ◽  
Incident Light ◽  
Selective Absorption ◽  
Smart Window ◽  
Direct Sunlight ◽  
Smart Windows

In this study, we analyzed angular-selective absorption in a guest–host liquid crystal (GHLC) cell for its application in smart windows. For reducing the energy consumption, angular-selective absorption is desired because the light transmitted through windows during the daytime is predominantly incident obliquely from direct sunlight. Owing to the absorption anisotropy of guest dichroic dyes, a GHLC cell can absorb the obliquely incident light, while allowing people to see through windows in a normal view. Therefore, the cell can provide a comfortable environment for occupants, and reduce the energy required for cooling by blocking the solar heat incident from the oblique direction. The GHLC cell can be switched between the transparent and opaque states for a normal view. The rising (falling) time was 6.1 (80.5) ms when the applied voltage was 10 V.

scholarly journals Enhanced Bandwidth Broadening of Infrared Reflector Based on Polymer Stabilized Cholesteric Liquid Crystals with Poly(N-vinylcarbazole) Used as Alignment Layer

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2238
Author(s):  
Limin Zhang ◽  
Qiumei Nie ◽  
Xiao-Fang Jiang ◽  
Wei Zhao ◽  
Xiaowen Hu ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Field ◽  
Cholesteric Liquid Crystal ◽  
Critical Role ◽  
Cholesteric Liquid Crystals ◽  
Smart Window ◽  
Alignment Layer ◽  
Thermal And Electrical Properties ◽  
Polymer Stabilized

Alignment layer plays a critical role on liquid crystal (LC) conformation for most LC devices. Normally, polyimide (PI) or polyvinyl alcohol (PVA), characterized by their outstanding thermal and electrical properties, have been widely applied as the alignment layer to align LC molecules. Here, we used a semi-conductive material poly(N-vinylcarbazole) (PVK) as the alignment layer to fabricate the cholesteric liquid crystal (CLC) device and the polymer-stabilized cholesteric liquid crystals (PSCLC)-based infrared (IR) reflectors. In the presence of ultraviolet (UV) irradiation, there are hole–electron pairs generated in the PVK layer, which neutralizes the impurity electrons in the LC–PVK junction, resulting in the reduction in the built-in electric field in the LC device. Therefore, the operational voltage of the CLC device switching from cholesteric texture to focal conic texture decreases from 45 V to 30 V. For the PSCLC-based IR reflectors with the PVK alignment layer, at the same applied electric field, the reflection bandwidth is enhanced from 647 to 821 nm, ranging from 685 to 1506 nm in the IR region, which makes it attractive for saving energy as a smart window.

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