scholarly journals Polymer Stabilized Liquid Crystal Smart Window with Flexible Substrates Based on Low-Temperature Treatment of Polyamide Acid Technology

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1869 ◽  
Author(s):  
Yang Zhang ◽  
Changrui Wang ◽  
Wei Zhao ◽  
Ming Li ◽  
Xiao Wang ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Temperature Treatment ◽  
Flexible Substrates ◽  
Smart Window ◽  
Alignment Layer ◽  
Low Temperature Treatment ◽  
Electro Optic ◽  
Lower Temperature ◽  
Polymer Stabilized ◽  
Pet Substrate

Polymer stabilized liquid crystal (PSLC) devices can be used as smart privacy windows that switch between transparent and opaque states. The polyimide alignment layer of a PSLC device is usually obtained by the treatment of polyamide acid (PAA) with temperatures over 200 °C. This hinders the fabrication of PSLC devices on flexible substrates, which melt at these high temperatures. In this work, the fabrication of a PSLC alignment layer using a lower temperature that is compatible with most flexible substrates, is demonstrated. It was found that the treatment of PAA at 150 °C could generate the same alignment for liquid crystals. Based on this, a PSLC device was successfully fabricated on a flexible polyethylene terephthalate (PET) substrate, demonstrating excellent electro-optic performances.

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.

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.

Electro-Optic Potential of Room and High Temperature Polymer Stabilised Blue Phase Liquid Crystal

2014 ◽  
Vol 895 ◽  
pp. 186-189 ◽  
Author(s):  
Md. Asiqur Rahman ◽  
Itaru Yamana ◽  
Yeap Guan Yeow ◽  
Suhana Binti Mohd Said ◽  
Munehiro Kimura
Keyword(s):  
Liquid Crystal ◽  
High Temperature ◽  
Cell Structure ◽  
Alignment Layer ◽  
Free Process ◽  
Electro Optic ◽  
Liquid Crystal System ◽  
Phase Liquid ◽  
Blue Phase ◽  
Polymer Stabilization

In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub-phases. Blue-phase liquid crystal holds the potential to become next-generation display and photonics device because of its sub-millisecond gray-to-gray response time, alignment-layer-free process, optically isotropic dark state, and cell gap insensitivity. The BPLC is a highly chiral liquid crystal system possessing crystal like unit cell structure and exist over a small temperature range (0.5-2 °C) between isotropic and chiral nematic (N*) thermotropic phase. The narrow phase range has been an intrinsic problem for blue phase, and a useful strategy of widening the phase is by adding polymer to form a polymer stabilised blue phase liquid crystal. In this paper, we demonstrate polymer stabilization using two different cases: a room temperature mixture containing E8, PE-5CNF and CPP-3FF, and a high temperature mixture using a single molecule blue phase liquid crystal material, TCB5. Comparison of the polymer stabilization effects on these two cases will be discussed, in the perspective of their potential in electro-optic applications.

Cell Gap Effects on Electro-Optic Performance of a Polymer-Stabilized Liquid Crystal Cell

2016 ◽  
Vol 28 (10) ◽  
pp. 1138-1141 ◽  
Author(s):  
Tae-Hoon Choi ◽  
Yeongyu Choi ◽  
Young-Jin Park ◽  
Jung-Wook Kim ◽  
Tae-Hoon Yoon
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystal Cell ◽  
Crystal Cell ◽  
Electro Optic ◽  
Polymer Stabilized ◽  
Gap Effects

Formation of Polymer Stabilized Ferroelectric Liquid Crystals using a Fluorinated Diacrylate

1999 ◽  
Vol 559 ◽  
Author(s):  
C. Allan Guymon ◽  
Christopher N. Bowman ◽  
Christopher N. Bowman
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Polymer Network ◽  
Isotropic Phase ◽  
Ferroelectric Liquid Crystals ◽  
Smectic C ◽  
Electro Optic ◽  
Polymerization Behavior ◽  
Mechanically Stabilized ◽  
Polymer Stabilized

ABSTRACTFerroelectric liquid crystals (FLCs) have shown great potential for use in electro-optic and display technology due to their inherently fast switching speeds and bistability. Recently, considerable research has been devoted to FLCs mechanically stabilized by a polymer network. The network is formed typically by in situ polymerization of a monomer dissolved in the FLC. Because of the inherent order in the FLC, the polymerization behavior may be significantly different than what might be expected in solution polymerizations. These deviations result largely from the segregation properties of the monomer in the liquid crystal. One class of monomers, namely fluorinated acrylates, is a likely candidate for inducing novel segregation, polymerization and electro-optic behavior in polymer stabilized ferroelectric liquid crystals (PSFLCs). The use of fluorinated moieties has a significant impact on the phase and polymerization behavior of liquid crystal systems. This study focuses on the polymerization of a fluorinated diacrylate, octafluoro 1,6-hexanediol diacrylate (FHDDA), to form PSFLCs and the consequent impact of the polymerization on the ultimate performance. Interestingly, as the temperature is increased and the order of the system decreases, a dramatic increase in the polymerization rate is observed. This increase is especially prominent for polymerizations in the smectic C* phase for which the rate is more than five times that exhibited at much higher temperatures in the isotropic phase. As with other monomer/FLC systems, the segregation of the monomer plays a role in this polymerization behavior as the monomer segregates between the smectic layers of the liquid crystal. The segregation properties also significantly impact the ultimate electro-optic properties. Both ferroelectric polarization and response time of the PSFLC change markedly with different polymerization temperatures, and approach values very close to those of the neat FLC under appropriate polymerization conditions. This behavior not only provides a unique mechanism for rate acceleration in PSFLCs, but also paves the way for new methods to optimize performance in these materials.

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