Electrooptical characterizations of polymer stabilized cholesteric liquid crystals

Guillard, Hervé; Sixou, P.; Reboul, L; Périchaud, A.

doi:10.1016/s0032-3861(01)00312-3

Cited by 48 publications

(37 citation statements)

References 17 publications

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“…The polymer concentration is greater close to the UP side than close to the DOWN one. Consequently, since the network-forming material is a nematic LC Broadband reflective cholesteric gels 1015 (infinite-pitch CLC), the pitch would have been expected to be longer close to the UP side and decreasing in a direction perpendicular to the UP substrate, as reported in the literature [6,22]. But this scenario is in apparent contradiction with the present reflection measurements, which correspond to the smallest reflection wavelength close to the UP side.…”

Section: Discussioncontrasting

confidence: 80%

“…The cell was kept at room temperature and, for polymerization purposes, illuminated for 30 min with UV light centred at 365 nm and with a power equal to 0.1 mW cm 22 as measured with a radiometer (UVR-365, Prolabo). In the following, the so-called asymmetrical conditions correspond to an irradiation from one single side (with a black substrate disposed under the 1010 S. Relaix et al…”

Section: Uv Light Curing Conditionsmentioning

confidence: 99%

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Broadband reflective cholesteric liquid crystalline gels: volume distribution of reflection properties and polymer network in relation with the geometry of the cell photopolymerization

2007

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The ultraviolet (UV) light-absorbing properties of the liquid crystal (LC) constituent during the photo-induced elaboration of a cholesteric LC (CLC) gel may induce the broadening of the reflection bandwidth of the material, a situation that is promoted by asymmetrical irradiation conditions (only one side of the cell is irradiated). The in situ structure of the polymer network, included in the LC, was investigated by transmission electron microscopy and the temperature dependence of the reflection properties examined; it is shown that the network has a structure gradient that is at the origin of the broadening phenomenon. The smallest reflection wavelength is related to the cell side from which the UV light beam came in. A priori, this situation was unexpected since it is shown that this part of the gel is enriched with nematic (infinite-pitch CLC) network-forming material. The result is discussed in relation to the variation of the reflection band characteristics with polymer concentration, which offers the opportunity for indirect access to the volume distribution of the cholesteric periodicities. For applications, broadband reflective cholesteric gels may be of interest for reflective polarizer-free displays or for the light management with smart electricallyswitchable reflective windows.

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Section: Discussioncontrasting

confidence: 80%

Section: Uv Light Curing Conditionsmentioning

confidence: 99%

Broadband reflective cholesteric liquid crystalline gels: volume distribution of reflection properties and polymer network in relation with the geometry of the cell photopolymerization

2007

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“…In the polymer stabilized cholesteric LCs (PSCLCs), a desired macroscopic orientation of Ch-LCs directors can be stabilized or frozen by the crosslinked network, in which PSCLCs are formed by photo-polymerization of a relatively small amount of a photo-reactive monomers dissolved in the nonreactive Ch-LCs [5][6][7][8][9][10][11]. The characteristic helical structure of the Ch-LCs impart unique optical properties such as reflecting circularly polarized component of light, the reflected wavelength of Ch-LCs is generated by the photonic band gaps (PBGs) from the periodical helical orientation.…”

Section: Introductionmentioning

confidence: 99%

Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

Jin

Xing

Jiewei

et al. 2015

Molecular Crystals and Liquid Crystals

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In this study, we developed a cholesteric liquid crystal (Ch-LCs) composite with a dual (both right-and left-) circularly polarized light reflection band by utilizing a polymer template method, where a glassy Ch-LCs oligomer (GCLCO) with left-handed helical structure containing azobenzene dopant (AD) was infiltrated into the polymer template with right-handed helical structure. Photo-optical, thermal as well as glass-forming properties of the Ch-LCs film with a dual circularly polarized light reflection band were investigated, trans-cis (E-Z) photoisomerization of the AD in the GCLCO induced pitch length shortenings in response to the formation of the Z isomers by 365 nm ultraviolet (UV) irradiation, resulting that the reflection band of left-handed circularly polarized component of light in the Ch-LCs composite after UV irradiation exhibited a blue shift.What is more, the changed reflected color could be fixed in Ch glassy solid by rapid cooling from their Ch temperatures to below glass transition temperature (T g ), in which the photo and thermal isomerization of the AD could not influence the Ch pitch any longer and the color was stably stored. This technique has great applications such as tunable lasers, optical sensors, and security technology.

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“…Therefore, it is impossible to get a white background display. Adding dense nano-particle-network into the chiral liquid crystal is the currently used method to broaden the spectral range, as patents and articles have been declared [2,3]. However, these methods brought some problems: the existing dense nano-particle-network in the liquid crystal will separate the interior of the liquid crystal into many domains, and the interface of the domains scatter incident light even in focal conic state.…”

Section: Introductionmentioning

confidence: 99%

Reflective spectrum broadened by nano-particle-network in chiral liquid crystals

Huang

Yang

Wang

2008

Front. Optoelectron. China

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Based on the analytical expression of the electromagnetic field solution of a helical symmetric dielectric material, the relationship between spectral reflectivity and birefringence of a chiral liquid crystal and the blue shift of the Bragg reflection in the condition of oblique incidence are presented in this paper. The theoretical results indicated that: 1) If birefringence (Dn) of the liquid crystal is greater than 0.2 and the thickness of the liquid crystal layer reaches 3mm, the liquid crystal layer will reflect more than 90% of the incident light; 2) To reflect the whole visible spectrum by Bragg reflection, Dn of the liquid crystals in plane alignment state should exceed 0.6; 3) When the incident beam inclines to 60u from the normal direction, the blue shift of the reflective spectrum will reach to 100 nm. On the other hand, since the Dn of the commercial chiral liquid crystals is not larger than 0.2, to get the entire visible reflective spectrum, it needs to introduce a polymer network into the liquid crystals and make a sagging structure on the surface of substrates. The contribution of the network is to establish random anchorage that makes the pitch varied, hence broadening the Bragg reflection spectra. The random distribution of the sagging structure on the surface substrate is used to induce random screw axes of the chiral liquid crystal, which not only causes a blue shift of Bragg reflection but also further stretches the reflection spectra. Experiments demonstrated that the Bragg reflection spectrum could be broadened from 80 nm to more than 120 nm, and the contrast reaches 4:1 by introducing both polymer network and sagging structure on the substrate surface cell.

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Electrooptical characterizations of polymer stabilized cholesteric liquid crystals

Cited by 48 publications

References 17 publications

Broadband reflective cholesteric liquid crystalline gels: volume distribution of reflection properties and polymer network in relation with the geometry of the cell photopolymerization

Broadband reflective cholesteric liquid crystalline gels: volume distribution of reflection properties and polymer network in relation with the geometry of the cell photopolymerization

Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

Reflective spectrum broadened by nano-particle-network in chiral liquid crystals

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