BISTABLE CHOLESTERIC REFLECTIVE DISPLAYS: Materials and Drive Schemes

Yang, Deng‐Ke; Huang, Xiaoyang; Zhu, Yang‐Ming

doi:10.1146/annurev.matsci.27.1.117

Cited by 98 publications

(71 citation statements)

References 17 publications

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“…Cholesteric liquid crystals (CLCs) are of great interest in various applications such as displays, light modulators, switchable diffraction gratings, liquid-crystal lasers and others [1][2][3][4][5]. This is determined by specific optical properties resulting from the helical ordering of director [6].…”

Section: Introductionmentioning

confidence: 99%

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

et al. 2016

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A reorientation of cholesteric liquid crystal with a large helix pitch induced by the electrically controlled ionic modification of the surface anchoring has been studied. In initial state, the cholesteric helix is untwisted completely owing to the normal surface anchoring specified by the cations adsorbed at the substrates. As a result, the homeotropic director configuration is observed within the cell. Under the action of dc electric field, one of the substrates becomes free from the layer of surface active cations, therefore, setting the planar surface anchoring. The latter, in turn, leads to the formation of the hybrid chiral structure. The threshold value and dynamic parameters have been estimated for this process as well as the range of control voltages, which do not allow the electrohydrodynamic instabilities. The twisted hybrid director configuration observed in the experiment has been analyzed by means of the simulation of polarization change of light propagating through the cholesteric layer with asymmetric (planar and homeotropic) surface anchoring on the cell substrates.

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Section: Introductionmentioning

confidence: 99%

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

et al. 2016

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“…[140] To reduce the power consumption of the various electrically switchable cholesteric-based LC windows, some form of bistable system could be envisioned. [141] Bistable systems consume energy only to switch from one state to another and no energy is required to remain in any one state. Earlier reports have provided some examples, such as the switchable scattering-toclear state system using the cholesteric/SmA phase.…”

Section: Outlook and Future Challengesmentioning

confidence: 99%

“…Earlier reports have provided some examples, such as the switchable scattering-toclear state system using the cholesteric/SmA phase. [82,[141][142][143][144][145] Of course, these mixtures often rely on polymer stabilization, with its concomitant challenges in reducing scattering in the visible spectrum.…”

Section: Outlook and Future Challengesmentioning

confidence: 99%

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

324

220

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(IR), here defined as light with wavelengths between 700 nm and 2500 nm, accounts for around 50% of the total energy emitted by the sun reaching Earth (Figure 1b), [3,4] and this light produces interior heating but is invisible to the unaided eye.The absorption of sunlight by building materials and passage of IR through transparent surfaces such as windows is responsible for much of the interior overheating of office rooms, automobile interiors, greenhouses, and other similar spaces. The use of artificial cooling and heating systems will only increase with the continued influence of global climate change, with energy used for cooling systems surpassing energy used for heating around the year 2070, and a 40 fold increase in air cooling energy use is expected by 2100. [5] By controlling the influx of radiant heat transfer, calculations show that more than 50% of the energy used in lighting, heating and cooling could be saved by deploying better control systems over only 18% of available window stock. [6] In areas with human inhabitants employing windows, more aspects must be considered than simply reducing the use of energy in the room: any switchable window used in, for example, a commercial office space has several other requirements that must be met before it may be installed. Among these requirement are reasonably fast switching speeds [7] (although for IR control, relatively longer times compared to visible light switching should be acceptable), good optical transparency with minimum haze, an acceptable device lifetime, [8] and functionality over a range of exterior temperatures. Controlling the excess of solar energy without compromising the visible transparency of the window is an important consideration for human health: maintaining inside/outside contact and daylighting are vital in retaining well-being and productivity, as well as providing economic and aesthetic gain by reducing the need for artificial lighting systems. [9,10] These are challenging goals for a window to realize.A number of materials have been developed over the past few decades to maintain indoor temperatures. Many of these focus on the opaque structural building elements like walls and roofing. [10][11][12][13] Other solutions target the transparent window, employing external mechanical shutters and blinds, [14] phase change materials (PCMs), [15] thermochromic materials, [16] aerogels, [17] trapped gas in fluid membranes, [18] and even phononic materials, [19] among other options. Indeed, controlling heat passage through the window in response to changing climate conditions is a great challenge; ideally, one would accomplish Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or trans...

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“…[5][6][7] When illuminated with white light, ChLCs reflect light of particular wavelengths dependent on the helical pitch of the LC phase. [8] According to well established theories, the selective reflection wavelength (l) of a ChLC is governed by Equation (1):…”

Section: Introductionmentioning

confidence: 99%

Influence of Helical Twisting Power on the Photoswitching Behavior of Chiral Azobenzene Compounds: Applications to High‐Performance Switching Devices

Alam

Yoshioka

Ogata

et al. 2007

Chemistry A European J

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Five photochromic chiral azobenzene compounds and one nonphotochromic chiral compound were synthesized and characterized by IR, 1H NMR spectroscopy, and elemental analysis. Cholesteric liquid crystalline phases were induced by mixing of the nonphotochromic chiral compound and one of the photochromic chiral azobenzene compounds in a host nematic liquid crystal (E44). The helical pitch of the induced cholesteric phase was determined by Cano's wedge method and the helical twisting power (HTP) of each sample was thus determined. The helical twisting powers of azobenzene compounds were decreased upon UV irradiation, due to trans-->cis photoisomerization of azobenzene molecules. Among the azobenzene compounds synthesized in our study, Azo-5, with isomannide (radical) as chiral photochromic dopant, showed the highest HTP and contrast ratio (Tmax/Tmin). Photoswitching between compensated nematic phase and cholesteric phase was achieved through reversible trans<-->cis photoisomerization of the chiral azobenzene molecules through irradiation with UV and visible light, respectively. Transmission rates (contrast ratios) increased with decreasing helical pitch length in the induced cholesteric phase. The influence of helical twisting power on the photoswitching behavior of chiral azobenzene compounds is discussed in detail.

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BISTABLE CHOLESTERIC REFLECTIVE DISPLAYS: Materials and Drive Schemes

Cited by 98 publications

References 17 publications

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

Infrared Regulating Smart Window Based on Organic Materials

Influence of Helical Twisting Power on the Photoswitching Behavior of Chiral Azobenzene Compounds: Applications to High‐Performance Switching Devices

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