Temperature Dependence of the Intrinsic Pitch in Induced Cholesteric Systems

Finkelmann, Heino; Stegemeyer, H.

doi:10.1002/bbpc.19780821206

Cited by 68 publications

(23 citation statements)

References 20 publications

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“…4) as experimentally observed for many dilute solutions of chiral dopants in nematic phases, see e.g. [5]. No significant system size effects appear, which rather could be assigned to the usual findings of higher order parameters in simulations of smaller systems than to effects of the applied boundary conditions which in fact allow the determination of the equilibrium properties of systems with periodic superstructures incommensurable to the comparably small system sizes studied.…”

Section: Binary Systems Of Achiral and Chiral Moleculesmentioning

confidence: 81%

“…For instance, dissolving a chiral compound in a nematic phase induces a cholesteric phase, which is characterised by its pitch and handedness. Here, the derivative of the inverse pitch with respect to the mole fraction of the chiral dopant is a suitable pseudoscalar quantity for the tendency of the chiral guest molecule to twist the nematic phase [5]. In order to obtain also symmetry adapted quantitative measures for the chiral induction considering the change of the suprastructural chirality dissolving chiral dopants in a chiral phase, a generalised definition has been introduced [6]: The pseudoscalar helical twisting power (HTP) e = ^-dp -l dx e xe =0 3 V / «., =o and the scalar achiral helical twisting power (AHTP) e = A dp -l A dx P jc" =0 dp -i A dx *"t =0…”

Section: Introductionmentioning

confidence: 99%

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Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power

Memmer

Janssen

1999

Zeitschrift Für Naturforschung A

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The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomeric dopants in the chiral surroundings of a cholesteric host phase has been determined.

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Section: Binary Systems Of Achiral and Chiral Moleculesmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power

Memmer

Janssen

1999

Zeitschrift Für Naturforschung A

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“…While this is easily explained for mixtures of different components through a different temperature dependence of the pitch [37,38], it is much more surprising in a single component system. The helical superstructure changes its handedness simply by temperature variation, going through a nematic director configuration.…”

Section: Propertiesmentioning

confidence: 99%

Chiral Liquid Crystals: Structures, Phases, Effects

2014

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The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.

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“…[13±21] The main principal underlying the photoinduced control of the optical properties of such materials is provided by the photoisomerization of chiral photochromic fragments, which is accompanied by changes in their anisometry and helix twisting power b. As is well known, [22] b is directly related to the concentration of chiral component x and helix pitch P in the helical supramolecular structure, which is responsible for the selective light-reflection maximum k max :…”

Section: Introductionmentioning

confidence: 99%

Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo-Optical Properties

Bobrovsky

Shibaev²

2002

Adv. Funct. Mater.

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A cholesteric mixture based on a menthyl‐containing copolymer, photosensitive chiral dopant, mesogenic diacrylate, and photoinitiating agent has been prepared. The mixture shows a selective light reflection in the visible light spectral region. The action of UV irradiation (313 or 365 nm) on the planar‐oriented films generates the occurrence of two parallel processes: E/Z (i.e., cis–trans) photoisomerization of the chiral dopant and photopolymerization of the diacrylate. The first process leads to the untwisting of the cholesteric helix and shifts the selective light‐reflection maximum to the long‐wavelength spectral region, whereas the second process leads to the development of a polymer network that fixes the helical supramolecular structure. As a result of a simultaneous occurrence of the two above‐mentioned processes, the shift in the selective light‐reflection maximum is thermally irreversible, even though the Z/E isomerization of the chiral dopant itself can be reversed by annealing. On irradiation with visible light (>450 nm), the dopant experiences the E/Z isomerization but photopolymerization is absent because the photoinitiator shows no absorption in this spectral region. In this case, the shift in the selective light‐reflection maximum can be reversed to its initial value by annealing, whereby the original helix pitch is recovered. The kinetic features of helix untwisting at different temperatures and light wavelengths were studied. The experimental data obtained in this work allow one to conclude that the as‐prepared mixture presents a new multifunctional material with “tunable” photo‐optical properties and may be used for recording and storage of optical information.

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Temperature Dependence of the Intrinsic Pitch in Induced Cholesteric Systems

Cited by 68 publications

References 20 publications

Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power

Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power

Chiral Liquid Crystals: Structures, Phases, Effects

Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo-Optical Properties

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