Computer simulation of chiral liquid crystal phases. IV. Intermolecular chirality transfer to rotamers in a cholesteric phase

Memmer, R.; Kuball, H.‐G.; Schönhofer, Alfred

doi:10.1080/02678299508031094

Cited by 20 publications

(11 citation statements)

References 24 publications

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“….,N}. The director, which spirals around the cholesteric axis, can be found by using an elegant method of Memmer et al, 19,20 where the cholesteric liquid crystal is mapped onto an achiral nematic liquid crystal. Assuming that the cholesteric axis is parallel to the z-axis, this is achieved by rotating the u ˆi-axes, which to a large extent are perpendicular to the cholesteric axis when the order parameter is high, by an angle Àj(z i ) = À2pz i /p, around this axis.…”

Section: Directors and Order Parametersmentioning

confidence: 99%

“…of the order of several hundred molecular lengths, so simulations are not feasible even with fast computers. Therefore, the algorithms were tested by simulating a molecular model originally devised by Memmer et al 19,20 where the molecules consisted of a string of six discotic Gay-Berne ellipsoids of revolution, [21][22][23] the centres of symmetry of which were aligned along a straight line and the axis vectors of which were perpendicular to this line and rotated with a constant angle relative to the axis vector of the adjacent ellipsoid in such a way that spiral shaped molecules were obtained. This system was found to form cholesteric liquid crystals with a rotation period of about five molecular lengths, so it could be studied by molecular dynamics simulation.…”

Section: Introductionmentioning

confidence: 99%

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Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Sarman

Laaksonen

2013

Phys. Chem. Chem. Phys.

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The lack of a centre of inversion in a cholesteric liquid crystal allows linear cross couplings between thermodynamic forces and fluxes that are polar vectors and pseudovectors, respectively. This makes it possible for a temperature gradient parallel to the cholesteric axis to induce a torque that rotates the director, a phenomenon known as the Lehmann effect or thermomechanical coupling. The converse is also possible: a torque applied parallel to the cholesteric axis rotates the director and drives a heat flow. In order to study this phenomenon, nonequilibrium molecular dynamics simulation algorithms and Green-Kubo relations evaluated by equilibrium molecular dynamics simulation have been used to calculate the Leslie coefficient, i.e. the cross coupling coefficient between the temperature gradient and the director angular velocity, for a model system composed of soft prolate ellipsoids of revolution interacting via the Gay-Berne potential augmented by a chiral interaction potential causing the formation of a cholesteric phase. It is found that the Leslie coefficient is two orders of magnitudes smaller than other transport coefficients such as the heat conductivity and the twist viscosity, so that very long simulations are required to evaluate it. The Leslie coefficient decreases with the pitch but it has not been possible to determine the exact functional dependence of this coefficient on the pitch. Since very long simulations have been performed to evaluate the Leslie coefficient, very accurate values have been obtained for the twist viscosity and the heat conductivity as a by-product and it is found that they are very similar to the values of the corresponding quantities in the achiral nematic phase that arises when the pitch goes to infinity.

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Section: Directors and Order Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Sarman

Laaksonen

2013

Phys. Chem. Chem. Phys.

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“…Recently, extensions of the Lebwohl-Lasher model, the lattice version of the Maier-Saupe model [18], to single-component systems of chiral molecules have also been investigated [19][20][21][22], Here, self-determined boundary conditions enabled the determination of the equilibrium pitch of cholesteric phases in dependence on temperature and chirality parameter whereas even a helix inversion has been observed. Chiral induction in liquid crystals has been studied in guest-host systems of rigid chiral Gay-Berne atropisomers and achiral flexible retainers, where a chirality transfer could be proven by an induced excess of chiral dopant conformers [23], and in a nematic phase in contact with a chiral surface [24], By means of computer simulation the HTP has been determined only for chiral dimers formed from uniaxial hard ellipsoids measuring the difference in chemical potentials of right-and left-handed dopants in a twisted nematic phase of achiral molecules stabilised by twisted boundary conditions [25]. Due to equilibrium pitch values typically in the order of several hundred molecular diameters the determination of the HTP from a direct simulation of induced cholesteric phases would require far larger than accessible system sizes using periodic boundary conditions, where the pitch must be commensurate with the simulation box length [26].…”

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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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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“…9 To model more complicated molecular structures, further studies represent molecules as composites of two Gay-Berne ellipsoids. 10 Soft-sphere potentials can also be joined together in a linear chain to represent molecules. Such molecules can be rigid 11 or semiflexible.…”

Section: -5mentioning

confidence: 99%

Monte Carlo simulation of liquid-crystal alignment and chiral symmetry-breaking

Selinger

et al. 2001

The Journal of Chemical Physics

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We carry out Monte Carlo simulations to investigate the effect of molecular shape on liquid-crystal order. In our approach, each model mesogen consists of several soft spheres bonded rigidly together. The arrangement of the spheres may be straight (to represent uniaxial molecules), Z-shaped (for biaxial molecules), or banana-shaped (for bent-core molecules). Using this approach, we investigate the alignment of the nematic phase by substrates decorated with parallel ridges. We compare results for wide and narrow ridge spacing and examine local order near the substrates, and show that our results are consistent with the predictions of Landau theory. We also investigate chiral symmetrybreaking in systems of bent-core molecules. We find a chiral crystalline phase as well as a nonchiral smectic-A phase, but not a chiral smectic-C phase.

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Computer simulation of chiral liquid crystal phases. IV. Intermolecular chirality transfer to rotamers in a cholesteric phase

Cited by 20 publications

References 24 publications

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

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

Monte Carlo simulation of liquid-crystal alignment and chiral symmetry-breaking

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