Cholesteric liquid crystals with an electrically controllable reflection bandwidth based on ionic polymer networks and chiral ions

Lu, Hongbo; Hu, Jiafu; Chu, Yutian; Xu, Wei; Qiu, Longzhen; Wang, Xianghua; Zhang, Guobing; Hu, Juntao; Yang, Jiaxiang

doi:10.1039/c5tc00730e

Cited by 18 publications

(10 citation statements)

References 25 publications

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“…On further applying the reverse DC bias with a suitable field, broadband was switched to narrowband as a result of uniform distribution of the chiral dopant throughout the thickness of the film (Figure c). Similar mechanisms using chiral ionic polymer networks in –Δε Ch‐LC has also been used to generate tunable broad‐to‐narrow bandwidth reflectors upon application of electric fields . These systems can be further optimized for real applications by tuning the broadband to the near infrared region and improving the transparency in the visible region.…”

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

“…Similar mechanisms using chiral ionic polymer networks in -Δε Ch-LC has also been used to generate tunable broad-to-narrow bandwidth reflectors upon application of electric fields. [100] These systems can be further optimized for real applications by tuning the broadband to the near infrared region and improving the transparency in the visible region.…”

Section: Reflection Based Technologiesmentioning

confidence: 99%

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Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

322

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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Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

Section: Reflection Based Technologiesmentioning

confidence: 99%

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

322

220

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“…One of the prior art is the photo‐induced reflection band tuning in a CLC constructed from a high helical twisting power ( HTP ) chiral dopant containing azo and binaphthyl groups . Another method is to introduce chiral ionic liquid (CIL) or nanomaterials such as nanoparticles, nanowires, and nanotubes into the CLCs to achieve broad bandwidth upon applying electric fields. Although the bandwidth is adjustable, voltages with high amplitudes, and multiple frequencies (DC/AC) are needed to operate the CLCs.…”

Section: Introductionmentioning

confidence: 99%

Effects of polymer network on electrically induced reflection band broadening of cholesteric liquid crystals

Yang

Bunning

et al. 2017

J. Polym. Sci. Part B: Polym. Phys.

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The reflection band of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy can be broadened by DC electric fields, which was ascribed to the pitch gradient caused by the motion of the structural chirality, that is, the polymer network. They systematically varied the mixture components, such as the photo‐initiator concentration, the monomer functionality, and the chiral dopant, to explore their influences on the reflection band broadening behavior. They learned how to control the polymer network morphology and ion density, which in turn determined the reflection bandwidth. By optimizing the mixture, they have greatly enhanced the broadening effect and achieved large bandwidth at low voltages. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 835–846

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“…Since these parameters are sensitive to a range of external stimuli, this means that there are numerous routes by which the wavelength of the band gap may be “tuned”. For example, research has shown that the pitch of the helix may be changed using mechanical forces, light, and magnetic and electric fields − whereas studies have shown that the relevant refractive indices may be changed using temperature and electric fields. − …”

Section: Introductionmentioning

confidence: 99%

“…This then leads to a subsequent loss of the photonic band gap when viewed along the normal of the glass substrates. In an attempt to maintain the geometry of a standing helix while using conventional planar electrodes at both substrates and still achieve wavelength tuning of the band gap, different methodologies have been explored. ,− For example, studies include using dc electric fields applied to chiral nematic LCs with a negative dielectric anisotropy (Δε < 0) to exploit an electromechanical effect, , doping ferroelectric LC compounds into chiral nematic LCs, using electrically commanded surfaces, or using the heliconical structure that can be observed in dimeric LCs whereby the bend elastic constant, K 3 , is much smaller than the twist elastic constant, K 2 …”

Section: Introductionmentioning

confidence: 99%

Wavelength Tuning of the Photonic Band Gap of an Achiral Nematic Liquid Crystal Filled into a Chiral Polymer Scaffold

et al. 2016

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We demonstrate electric-field-induced wavelength tuning of the entire photonic band gap of an achiral nematic liquid crystal (LC) filled into a chiral polymer scaffold. This chiral polymer scaffold has been formed by creating a template of a chiral nematic LC phase, which remarkably does not compromise the optical finesse of the band gap when compared to that of a conventional, polymer-stabilized chiral nematic LC. We present results on the spectral shift and temporal evolution of the photonic band gap in the presence of an external ac electric field. It is shown that initially there is a rapid (τ ≈ 1 ms) blue-shift of the long-wavelength band-edge followed by a considerably slower blue-shift (τ ≈ 6.5 s) of the entire band gap. We compare the results with those obtained for a polymer-stabilized chiral nematic LC where only a blue-shift of the long-wavelength band-edge is observed. Consequently, we find that for the templated sample the tuning range is more than a factor of 2 greater than that observed for the polymer-stabilized chiral nematic LC for the same range of electric field amplitudes. It is also found that there is little in the way of hysteresis upon increasing and decreasing the applied electric field magnitude. Finally, we present experimental evidence that suggests that the blue-shift of the entire band gap is due to an additional tuning mechanism present only for the case of the templated samples. This is believed to be caused by a contraction of the pitch that results from a translational motion of the polymer network. The greater tuning range observed in these templated samples is potentially important for the development of tunable 1-dimensional photonic band gaps and LC lasers. Furthermore, it avoids the use of dc electric fields that can lead to long-term issues regarding stability.

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Cholesteric liquid crystals with an electrically controllable reflection bandwidth based on ionic polymer networks and chiral ions

Abstract: The reflection bandwidth can be tuned dynamically by electric fields in the visible wavelength regime.

Cited by 18 publications

References 25 publications

Infrared Regulating Smart Window Based on Organic Materials

Infrared Regulating Smart Window Based on Organic Materials

Effects of polymer network on electrically induced reflection band broadening of cholesteric liquid crystals

Wavelength Tuning of the Photonic Band Gap of an Achiral Nematic Liquid Crystal Filled into a Chiral Polymer Scaffold

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