Cholesteric polymers in electric fields

Shibaev, Valéry; Talroze, R. V.; Korobeinikova, I. A.; Platè, N.A.

doi:10.1080/02678298908033181

Cited by 9 publications

(7 citation statements)

References 14 publications

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“…The higher energy for the DM(⊥) gratings leads to slowing down of the switching “On” process, as expected. These values are close to the activation energies (200–250 kJ mol −1 ) of electroinduced untwisting of the helix pitch for the cholesteric polymers as reported previously . On the other hand, the switching “Off” activation energies were calculated as 76 and 155 kJ mol −1 for DM(//) and DM(⊥) gratings, respectively.…”

Section: Resultssupporting

confidence: 88%

Electroinduced Diffraction Gratings in Cholesteric Polymer with Phototunable Helix Pitch

Ryabchun

Bobrovsky

Stumpe

et al. 2015

Advanced Optical Materials

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cholesteric mesophase is the selective light refl ection. The maximum refl ection wavelength is determined by the simple Equation ( 1) max nP λ =where n is the average refractive index of the material and P is the helix pitch. According to this relation, the variation of the helix pitch simultaneously changes the wavelength of light refl ection. The specifi c values of helix pitch depend on the chemical structure of the substances forming the cholesteric phase. In the most cases the cholesteric mesophase is formed by doping of nematic liquid crystals with a chiral additive (dopant) possessing a proper helical twisting power, β . This phenomenological parameter characterizes the ability of the dopant to twist the nematic structure according to Equation ( 2)where X is the concentration of the chiral dopant. This value strongly depends on the geometry of the chiral fragments and molecular interactions (steric, van der Waals, etc.) between the mixture components. These relations between chiral dopants structure and helical twisting power allowed one to create ways for phototuning of the helix pitch. [9][10][11] In many previously studied systems light exposure induces the photochemical E/Z isomerization of aromatic anisometric part of a chiral compound resulting in the formation of a bent-shaped Z-isomer having lower β-values compared to the initial rodlike E-isomer ( Figure 1 ).One of the most interesting and important areas of CLCs application is related to creation of the diffraction gratings. We can distinguish, at least, fi ve different ways to produce phase gratings in CLC systems. Let us briefl y describe each of them.1) The fi rst method is based on the application of the holographic technique to produce the volume phase gratings (refractive index modulation) and/or surface relief gratings (SRG) in photochromic (in most cases azobenzene-containing) cholesteric polymer systems. [12][13][14][15][16][17] In the majority instances the photosensitive moieties are mainly used for the photo-orientation or photo-induced mass transfer. However, there is an example of "dual" photo-recording consisting of For the fi rst time the cholesteric mixture containing nematic polymer with small amount of chiral-photochromic dopant is used for electroinduced diffraction gratings production. The gratings are obtained by applying electric fi eld to the planar-aligned cholesteric polymer layer causing its periodical distortion. Material developed permits manipulating supramolecular helical structure by means of UV exposure resulting in helix untwisting. Photo-controlling of helix pitch brings to change parameters of the electroinduced gratings. Due to macromolecular "nature" of the material one can easily stabilize electroinduced gratings by fast sample cooling. All-known cholesteric grating types are realized in the studied polymer material. It is observed that the grating vector can be oriented along or perpendicular to the rubbing direction of the cell. It is shown that the diffraction effi ciency is dictated by grating type and...

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Section: Resultssupporting

confidence: 88%

Electroinduced Diffraction Gratings in Cholesteric Polymer with Phototunable Helix Pitch

Ryabchun

Bobrovsky

Stumpe

et al. 2015

Advanced Optical Materials

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“…The study of the influence of the degree of polymerization on the elastic moduli is also worthy of our attention. The electro optical investigations of the cholesteric copolymers with different molar masses performed in [68,72] have shown, that the change of the DP with the limits of 50 to 160 has almost no effect on the value of k22 ~ (4 -7)10 7 din, which coincides in order of magnitude with the twist elasticity constants of low-molar-mass nematic-cholesteric mixtures.…”

Section: Eledrooptical Effects In Comb-shaped Liquid-crystalline Polymentioning

confidence: 92%

“…In this section we do not intend to review the abundant literature related to the electroopitcal properties of LC polymers because the certain analysis of these aspects was done some time ago by different authors [14,15,163,67,68]. In this section, we will limit ourselves to the consideration of some electrooptical phenomena (in combshaped LC polymers) which can be used for the creation of new polymeric materials with unusual optical properties and in particular for the preparation of highly-oriented polymeric films for photo optical applications.…”

Section: Low-molar-mass Liquid Crystals In Electric Fields (Field Effmentioning

confidence: 99%

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Comb-Shaped Polymers with Mesogenic Side Groups as Electro- and Photooptical Active Media

Shibaev¹,

Kostromin²,

Ivanov³

1996

Polymers as Electrooptical and Photooptical Active Media

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“…Some of the special chemical structures are known as cholesteric liquid crystalline, which comes from "cholesterol" with indicating light circulativity. This sort of LCP is studied for the display application field 9 , and it is not in scope of this book. .…”

Section: Fig1-6 Type Of Liquid Crystalline Polymermentioning

confidence: 99%

liquid-crystalline polymer

2014

The IUPAC Compendium of Chemical Terminology

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Cholesteric polymers in electric fields

Cited by 9 publications

References 14 publications

Electroinduced Diffraction Gratings in Cholesteric Polymer with Phototunable Helix Pitch

Electroinduced Diffraction Gratings in Cholesteric Polymer with Phototunable Helix Pitch

Comb-Shaped Polymers with Mesogenic Side Groups as Electro- and Photooptical Active Media

liquid-crystalline polymer

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