Tuning of a cholesteric filter having a negative dielectric anisotropy

Natarajan, Lalgudi V.; Wofford, Jeremy M.; Tondiglia, Vincent P.; Sutherland, Richard L.; Siwecki, Stephen A.; Koerner, Hilmar; Vaia, Richard A.; Bunning, Timothy J.

doi:10.1117/12.730860

Cited by 10 publications

(13 citation statements)

References 3 publications

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“…A number of Ch-LC based narrowband reflectors, both in visible and infrared regions, have also been developed which can tune the position of reflection notch within a limited wavelength region in presence of an electric field. [90,91] Such narrow bandwidth reflectors can influence only a minor fraction of infrared light, and would have only limited impact on interior temperatures. Binet et al have fabricated broadband infrared reflectors by inter-diffusing two layers of different pitch lengths, consisting of polymer stabilized siloxane and non-reactive LC mesogens.…”

Section: Reflection Based Technologiesmentioning

confidence: 99%

“…[91] This thermal tuning was attributed to the pre-transitional effect of smectic-to-cholesteric phase transition. As the infrared energy from the sun increases continuously from far to near infrared region, with this method a lesser-to-greater amount of infrared energy can be reflected on continual increase in temperature.…”

Section: Reflection Based Technologiesmentioning

confidence: 99%

“…Upon exposure to an electric field, they could be switched between planar (reflective state) to homeotropic (transparent state) orientations (Figure ). A number of Ch‐LC based narrowband reflectors, both in visible and infrared regions, have also been developed which can tune the position of reflection notch within a limited wavelength region in presence of an electric field . Such narrow bandwidth reflectors can influence only a minor fraction of infrared light, and would have only limited impact on interior temperatures.…”

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

“…Natarajan et al have demonstrated a remarkable blue shift of a narrow band reflector from 2300 to 500 nm on increasing the ambient temperature, as shown in Figure 18 . This thermal tuning was attributed to the pre‐transitional effect of smectic‐to‐cholesteric phase transition.…”

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

See 4 more Smart Citations

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

337

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: Reflection Based Technologiesmentioning

confidence: 99%

Section: Reflection Based Technologiesmentioning

confidence: 99%

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

Section: Dynamic Ir Regulating Windowmentioning

confidence: 99%

See 3 more Smart Citations

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

337

220

View full text Add to dashboard Cite

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Electrically Induced Splitting of the Selective Reflection in Polymer Stabilized Cholesteric Liquid Crystals

Radka

King

McConney

et al. 2020

Advanced Optical Materials

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axis the wavelengths where the Bragg condition is met are given by Equa tions (2) and (3): nP λ = c (2) nP λ ∆ = ∆ (3) Due to the orientational dependence of the refractive index of the liquid crystal, the central wavelength of the Bragg con dition (λ c) is dependent on the average refractive index (n ‾) while the bandwidth of wavelengths that meet the Bragg con dition (∆λ) is dependent on the birefrin gence (∆n) of the liquid crystal. In a CLC, unpolarized light incident upon the material can be evaluated as two modes with oppositely circularly polarized wavevectors. When the Bragg condition is met, one mode is real and can propagate through the material, while the other is imaginary and cannot propagate and is reflected. Outside of the Bragg condition both modes are real and light is transmitted. Therefore, a CLC acts as a polari zation filter across selective wavelengths. Within the reflection regime the CLC reflects light with a matching handedness to the phase, transmitting light with the opposite handedness. As a result unpolarized light has reflection efficiency of 50% for a singular CLC phase. [3] Dynamic control of the selective reflection of CLCs has been subject to previous examination. Both thermal and optical con trol of the selective reflection have been widely explored. In the case of thermal control, thermochromic effects have been docu mented enabled by distinctive phase transitions (e.g., SmA to CLC), temperature dependence of the HTP of chiral dopants, and solubility. [4-8] Optical control of the selective reflection of CLCs has also been explored through the introduction of photo chromic groups (e.g., azobenzene) in either the LC or the dopant, that affect the periodicity or the refractive index of the medium upon irradiation. [9-13] However, thermal and optical regulation of the selective reflection of the CLC phase can be subject to limitations due to slow response times and environmental sensitivity. Com paratively, electrical control of the selective reflection of the CLC phase has the potential to be both rapidly addressable and robust to changes in environment (e.g., temperature or ambient light). Extensive prior research has document approaches to electrically adjust the optical properties of the CLC phase by using patterned electrodes, physical deformation of substrates, or via frequency dependent dielectric properties in LCs. [14-16] In some sense, the common theme of these efforts is that these approaches circumvent physical limits that prevent the periodic Electrical reconfiguration of the cholesteric liquid crystal phase is subject to extensive prior research. Here, a distinctive composition that allows the typically singular selective reflection to be split into two distinct and tunable selective reflections with an electric field is reported. The distinctive electro-optic phenomena (reflection notch splitting) are shown to be composition dependent and enabled by the introduction of appreciable amounts of side chain liquid crystalline mesogens. Functional opportunities enabled by ...

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Toward Full‐Color Tunable Chiroptical Electrothermochromic Devices Based on a Supramolecular Chiral Photonic Material

Jiang

Chang

Lin

et al. 2021

Advanced Optical Materials

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Traditional electrochromic devices change the color of electrochromic materials by mainly transforming the absorption band of the materials electrically, which leads to low schedulable color selection and color performance of such materials after electrochromism. Although the addition of an interference‐enhanced nanocavity can improve this issue, achieving full‐color controllability on a single electrochromic device is still a huge challenge. This study first demonstrates a near‐full‐color tunable chiroptical electrothermochromic device using a supramolecular chiral photonic material called ferroelectric liquid crystal (FLC)‐doped cholesteric liquid crystal (CLC) (FLC‐CLC). Experimental results show that the pitch of the CLC can be elongated significantly by doping a low concentration of FLC (≈4 wt%) such that the photonic bandgap (PBG) redshifts from blue to the shortwave near‐infrared region at near room temperature. Based on this fascinating feature, the PBG of the FLC‐CLC can be tuned electrically over the entire visible region with high color performance at near room temperature in a low‐voltage range (≤3 V) via the efficient electrothermal effect of the indium‐tin‐oxide‐coated substrate of the sample. Two potential low‐voltage tunable applications based on electrothermochromic FLC‐CLC materials, namely, a broadband tunable laser and a near‐full‐color tunable coaxial microfibric textile, are demonstrated in the study.

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Tuning of a cholesteric filter having a negative dielectric anisotropy

Cited by 10 publications

References 3 publications

Infrared Regulating Smart Window Based on Organic Materials

Infrared Regulating Smart Window Based on Organic Materials

Electrically Induced Splitting of the Selective Reflection in Polymer Stabilized Cholesteric Liquid Crystals

Toward Full‐Color Tunable Chiroptical Electrothermochromic Devices Based on a Supramolecular Chiral Photonic Material

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