The influence of helical twisting power on the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture

Lu, Hongbo; Song, Zhigang; Zhang, Jun; Lv, Guoqiang

doi:10.1080/02678292.2013.868939

Cited by 14 publications

(3 citation statements)

References 19 publications

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“…The thickness of films affected mainly the maximum transmittance at off-state. [20][21][22] As mentioned earlier, sample 2 achieved maximum transmittance. When a field was applied on samples, the ion-doped NLC materials became turbulent.…”

Section: Liquid Crystalsmentioning

confidence: 73%

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

et al. 2015

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This article proposes a methodology to prepare polymer dispersed liquid crystal (PDLC) films working in the reverse-mode operation, where the ion-doped nematic liquid crystals (NLCs) with negative dielectric anisotropy (Δε) were locked by polymer walls. On-state and off-state of films were controlled by an electric field. In the absence of an electric field, it appears to be transparent. In the field, the homogeneous alignment NLCs form dynamic scattering, giving rise to opaque. The effect of the cylindrical holes with different diameters of photo masks and liquid crystal Δε on the electro-optical properties and transmittance wavelength range of 400-3000 nm light of samples were investigated. It was found that it exhibited very good electro-optical characteristics, high contrast ratio and excellent infrared energy-efficient of films used as switchable windows.Keywords: reverse-mode polymer dispersed liquid crystal; polymer walls; nematic liquid crystal; negative dielectric anisotropy; electro-optical properties IntroductionPolymer dispersed liquid crystal (PDLC) films are technologically important class of materials that find numerous applications as electrically switchable optical devices.[1-3] PDLC films are formed by liquid crystal (LC) microdroplets embedded in a polymer matrix. They can exhibit either a droplet morphology in which droplets of LC are embedded in a polymer matrix, or a polymer ball morphology in which the LC takes up the voids and the crevices of a network structure formed by small polymer balls. In the normal-mode operation, they are in an opaque state (offstate) and can be turned into a transparent state (onstate) by controlling the LC molecule orientation by means of a suitable voltage. The reverse-mode PDLC films are transparent in its off-state and can be turned into an opaque on-state. A greater interest has been aroused by reverse-mode PDLC films that are useful as switchable windows, automotive applications [4,5] and used in a wide range of applications that need a transparent state in the absence of any applied voltage.Several authors have reported examples of reverse-mode PDLC films obtained by modification of the polymer surface energy,[6] by functionalising the LC/polymer matrix interface,[7] by using dualfrequency addressable LC,[8] by means of rough surfaces [9,10] or by increasing the LC content. [11]

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Section: Liquid Crystalsmentioning

confidence: 73%

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

et al. 2015

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“…The SEM images demonstrate spiral platelet single crystals with screw dislocations during crystal growth, providing further insights into the staggered racemes on the surface layer. Moreover, various studies use SEM to characterize twisting processes, such as molecular crystals, , polymers, − and semiconductors. , Recently, the elastic Co-based nanohelices were reported, whose structure can achieve a twisting–untwisting switch process . Apart from the complexity of crystal growth processes, SEM imaging is anticipated to reveal additional distinctive nanohelices and provide valuable insights for a deep comprehension of the twisting phenomenon.…”

Section: Electron Microscopy Imagingmentioning

confidence: 99%

Chirality Determination of Nanocrystals by Electron Crystallography

Wang,

Chu

et al. 2024

J. Phys. Chem. Lett.

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Chirality is a common phenomenon in nature and plays an important role in the properties of matter. The rational synthesis of chiral compounds and exploration of their applications in various fields require an unambiguous determination of their handedness. However, in many cases, determinations of the chiral crystal structure and chiral morphology have been a challenging task due to the lack of proper characterization methods, especially for nanosized crystals. Therefore, it is crucial to develop novel and efficient characterization methods. Owing to the strong interactions between matter and electrons, electron crystallography has become a powerful tool for structural analysis of nanomaterials. In recent years, methods based on electron crystallography, such as high-resolution electron microscopy imaging and electron diffraction, have been developed to unravel the chirality of nanomaterials. This brings new opportunities to the design, synthesis, and applications of versatile chiral nanomaterials. In this perspective, we summarize the recent methodology developments and ongoing research of electron crystallography for chiral structure and morphology determination of nanocrystals, including inorganic and organic materials, as well as highlight the potential and further improvement of these methods in the future.C hirality is a geometric property of a rigid object being nonsuperposable on its mirror image. 1 In nature, chirality is ubiquitous at multiple levels, from subatomic particles, organic molecules such as amino acids, macromolecules including proteins and DNA, macroscopic entities like sea shells, to even spiral galaxies. 2 Chirality has attracted great interest from multidisciplinary fields, including chemistry, biology, pharmacy, and materials science. 3 The Nobel Prize in Chemistry has recognized outstanding research in chiral synthesis and asymmetric catalysis twice in the past two decades. 4,5 In the pharmaceutical industry, more than half of clinical drugs belong to chiral molecules. 6 Moreover, chiral materials exhibit a wide range of exploitable properties, including optical behavior, enantioselectivity, ferroelectricity, electrochemical properties, and biological activity. 7−10 These cumulative factors highlight the significance of studying chirality in various scientific fields.With the rapid development of synthesis and applications of chiral compounds, one important and challenging task becomes prominent: how to effectively characterize the handedness of chiral materials. One of the difficulties is that two enantiomers usually exhibit similar physical and chemical properties, which makes it not easy to distinguish them using common characterization methods. Chirality of nanocrystals can be divided into two categories: chiral morphology and chiral crystal structure (Figure 1). Chiral morphology is a macroscopic property of a material. For example, some chiral materials show a special morphology (such as a helical shape). However, when we talk about chiral crystal structure, it means that the spa...

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“…This was explained by a transition from a non-uniform pitch distortion into a uniform pitch gradient when the cell gap increases [28]. There are also studies demonstrated that the polymer network deformation and helical twisting power of chiral dopants could influence the electrically induced dynamic response of the PSCLC based cells [39,40].…”

Section: Introductionmentioning

confidence: 99%

Cell thickness dependence of electrically tunable infrared reflectors based on polymer stabilized cholesteric liquid crystals

Haan

Khandelwal

et al. 2017

Sci. China Mater.

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We reported here the fabrication of the electrically tunable infrared (IR) reflectors based on the polymer stabilized cholesteric liquid crystal (PSCLC) with negative dielectric anisotropy. A systematic study of the influence of cell gap on the electrically tunable reflection bandwidth was performed. When a direct current (DC) electric field was applied, the reflection bandwidth red shifted in the cells with small cell gap, whereas the bandwidth broadening was observed in the cells with large cell gap. It is therefore reasonable to deduct that the reflection is dictated by the pitch gradient steepness which strongly relies on the cell thickness. The results reveal that for making PSCLC based IR reflector windows with electrically induced bandwidth broadening, a minimal cell gap thickness is required. The resulted IR reflectors possess a short native switching time and long-term operation stability, and are potentially applicable as smart energy saving windows in buildings and automobiles.

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The influence of helical twisting power on the electro-optical properties of reverse-mode polymer-stabilised cholesteric texture

Cited by 14 publications

References 19 publications

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

Chirality Determination of Nanocrystals by Electron Crystallography

Cell thickness dependence of electrically tunable infrared reflectors based on polymer stabilized cholesteric liquid crystals

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