A new twist on cholesteric films by using reactive mesogen particles

Beltrán-Gracia, Eduardo; Parri, Owain

doi:10.1039/c5tc02920a

Cited by 36 publications

(39 citation statements)

References 24 publications

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“…This is in stark contrast to the case of droplets, which suffer from severe defect generation during polymerisation, even at only 4.7% reactive component 10 . To turn the shell completely into a solid (which may actually not be desirable, as discussed below), all components of the cholesteric mixture would need to be replaced by reactive molecules 25 . However, even using just a single achiral reactive mesogen we can polymerise a sufficient fraction of the shell to ensure robustness against mechanical shock and shells pushing against each other, thereby allowing easy manipulation and greatly expanding the application opportunities for the shells.…”

Section: Resultsmentioning

confidence: 99%

High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication

Geng

Noh

Drevenšek‐Olenik

et al. 2016

Sci Rep

144

163

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Monodisperse cholesteric liquid crystal microspheres exhibit spherically symmetric Bragg reflection, generating, via photonic cross communication, dynamically tuneable multi-coloured patterns. These patterns, uniquely defined by the particular sphere arrangement, could render cholesteric microspheres very useful in countless security applications, as tags to identify and authenticate their carriers, mainly physical objects or persons. However, the optical quality of the cholesteric droplets studied so far is unsatisfactory, especially after polymerisation, a step required for obtaining durable samples that can be used for object identification. We show that a transition from droplets to shells solves all key problems, giving rise to sharp patterns and excellent optical quality even after polymerisation, the polymerised shells sustaining considerable mechanical deformation. Moreover, we demonstrate that, counter to prior expectation, cross communication takes place even between non-identical shells. This opens additional communication channels that add significantly to the complexity and unique character of the generated patterns.

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Section: Resultsmentioning

confidence: 99%

High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication

Geng

Noh

Drevenšek‐Olenik

et al. 2016

Sci Rep

144

163

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“…Reflection properties of Ch‐LCs, similar to all other standard Bragg reflectors, are incident angle dependent. To reduce the angular dependency of Bragg reflection based smart windows, polymer stabilized Ch‐LC particles could be a good alternative . Other advantages of using the polymer stabilized Ch‐LC particles are that they do not require an alignment layer on the substrate used to fabricate the device.…”

Section: Outlook and Future Challengesmentioning

confidence: 99%

“…To reduce the angular dependency of Bragg reflection based smart windows, polymer stabilized Ch-LC particles could be a good alternative. [137] Other advantages of using the polymer stabilized Ch-LC particles are that they do not require an alignment layer on the substrate used to fabricate the device. Moreover, they can be scaled up in large quantities for effective commercial application, unlike the polymer stabilized cholesteric films.…”

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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“…The formation of complex cholesteric structures expands the scope of applications of PDLC films, for instance, in electrically controlled reflectors [ 36 , 37 ], color electronic paper [ 38 ], printable temperature sensors [ 39 ], systems for lasing [ 40 , 41 , 42 ], solar cells [ 43 ], etc. On the other hand, the structure control inherent in flat CLC layers comes with its own difficulties.…”

Section: Introductionmentioning

confidence: 99%

Polymer Dispersed Cholesteric Liquid Crystals with a Toroidal Director Configuration under an Electric Field

et al. 2021

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The electro-optical properties of polymer dispersed liquid crystal (PDLC) films are highly dependent on the features of the contained liquid crystal (LC) droplets. Cholesteric LC droplets with homeotropic boundaries can form several topologically different orientational structures, including ones with single and more point defects, layer-like, and axisymmetric twisted toroidal structures. These structures are very sensitive to an applied electric field. In this work, we have demonstrated experimentally and by computer simulations that twisted toroidal droplets reveal strong structural response to the electric field. In turn, this leads to vivid changes in the optical texture in crossed polarizers. The response of droplets of different sizes were found to be equivalent in terms of dimensionless parameters. In addition, the explanation of this phenomenon showed a comparison of theoretical and experimental structural response curves aids to determine the shape of the droplet. Finally, we demonstrated that the addition of a dichroic dye allows such films to be used as optical filters with adjustable color even without polarizers.

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A new twist on cholesteric films by using reactive mesogen particles

Cited by 36 publications

References 24 publications

High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication

High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication

Infrared Regulating Smart Window Based on Organic Materials

Polymer Dispersed Cholesteric Liquid Crystals with a Toroidal Director Configuration under an Electric Field

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