A cholesteric liquid crystal smart window with a low operating voltage

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.

Download Full-text

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

Optical Materials Express ◽

10.1364/ome.8.000691 ◽

2018 ◽

Vol 8 (3) ◽

pp. 691 ◽

Cited By ~ 11

Author(s):

Chun-Wei Chen ◽

Alyssa N. Brigeman ◽

Tsung-Jui Ho ◽

Iam Choon Khoo

Keyword(s):

Liquid Crystal ◽

Cholesteric Liquid Crystal ◽

Smart Window

Download Full-text

Smart Window with Active-Passive Hybrid Control

Materials ◽

10.3390/ma13184137 ◽

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.

Download Full-text

Bistable Smart Window Based on Ionic Liquid Doped Cholesteric Liquid Crystal

IEEE Photonics Journal ◽

10.1109/jphot.2017.2653862 ◽

2017 ◽

Vol 9 (1) ◽

pp. 1-7 ◽

Cited By ~ 13

Author(s):

Zhaojue Lan ◽

Yong Li ◽

Haitao Dai ◽

Dan Luo

Keyword(s):

Ionic Liquid ◽

Liquid Crystal ◽

Cholesteric Liquid Crystal ◽

Smart Window

Download Full-text

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

Polymers ◽

10.3390/polym13142238 ◽

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.

Download Full-text

Effect of Ferroelectric Nano-powder on Electrical and Acoustical Properties of Cholesteric Liquid Crystal

Non-Metallic Material Science ◽

10.30564/omms.v2i1.1821 ◽

2020 ◽

Vol 2 (1) ◽

Author(s):

Santosh Mani ◽

Madhavi Pradhan ◽

Archana Sharma ◽

Sameer Hadkar ◽

Krishnakant Mishra ◽

...

Keyword(s):

Liquid Crystal ◽

Cholesteric Liquid Crystal ◽

Fast Response ◽

Close Packing ◽

Operating Voltage ◽

Nano Materials ◽

Preparation Methods ◽

Acoustical Properties ◽

Nano Powder ◽

Rao’S Constant

Ferroelectric nano-materials are very sensitive to several external stimuli and have attracted great deal of attention due to their property of improving various properties such as photoluminescence, higher polarization, fast response time, low operating voltage and improved conductivity. For enhancing the physical properties, a proper selection of nano-materials for liquid crystals depends upon various factors such as size, shape, preparation methods, surfactant concentration and amount of doping materials. In the present study an attempt is made to study electrical and acoustical properties of cholesteric liquid crystal after dispersing ferroelectric nano-powder of Barium Titanate (BaTiO3). In addition with this particle size and surface area of pure and nono-particle dispersed liquid crystal were also measured. Our investigation shows increase in Rao’s constant or molar sound velocity, which indicates increase in molecular density indicating a close packing of the material. The measurement of dielectric relaxation at different frequencies gives information about the dynamics of polar groups and molecular motion.

Download Full-text