Search results for "Liquid Crystal"

Structural defects in smectic c* liquid crystals

1992

In this paper the structure of a smectic c* liquid crystalline material which can be switched in an electric field is investigated by electron microscopic techniques. Using this method the director field is revealed and typical disclinations observed. Analysis of these features enables the elastic anisotropy of the material to be calculated. Sample description. For our structure investigations a liquid crystalline material (4-(3-(s)-methyl-2-(s)-chloropentanoyloxy)-4'-octyloxy-biphenyl) with two chiral centres was synthesised using known procedures [I]. This material has been investigated by broadband dielectric spectroscopy, the softand Goldstone modes were analysed [2a] as well as the hig…

Coexistence Curve Singularities at Critical End Points

1997

We report an extensive Monte Carlo study of critical end point behaviour in a symmetrical binary fluid mixture. On the basis of general scaling arguments, singular behaviour is predicted in the diameter of the liquid-gas coexistence curve as the critical end point is approached. The simulation results show clear evidence for this singularity, as well as confirming a previously predicted singularity in the coexistence chemical potential. Both singularities should be detectable experimentally.

Isotropic-nematic interfacial tension of hard and soft rods: Application of advanced grand canonical biased-sampling techniques

2005

Coexistence between the isotropic and the nematic phase in suspensions of rods is studied using grand canonical Monte Carlo simulations with a bias on the nematic order parameter. The biasing scheme makes it possible to estimate the interfacial tension gamma in systems of hard and soft rods. For hard rods with L/D=15, we obtain gamma ~ 1.4 kB T/L^2, with L the rod length, D the rod diameter, T the temperature, and kB the Boltzmann constant. This estimate is in good agreement with theoretical predictions, and the order of magnitude is consistent with experiments.

Ideal glass transitions for hard ellipsoids

2000

For hard ellipsoids of revolution we calculate the phase diagram for the idealized glass transition. Our equations cover the glass physics in the full phase space, for all packing fractions and all aspect ratios X$_0$. With increasing aspect ratio we find the idealized glass transition to become primarily be driven by orientational degrees of freedom. For needle or plate like systems the transition is strongly influenced by a precursor of a nematic instability. We obtain three types of glass transition lines. The first one ($\phi_c^{(B)}$) corresponds to the conventional glass transition for spherical particles which is driven by the cage effect. At the second one ($\phi_c^{(B')}$) which oc…

Thermal fluctuation effects in ferroelectric liquid-crystal polarization reversal: Light scattering from a transient domain-wall foam

1991

Thermal orientation fluctuations of the director field during electric-field-induced polarization reversal in ferroelectric liquid crystals lead to the nondeterministic formation of a transient domain-wall foam that strongly scatters light. This foam comprises domains of molecules that have reoriented locally in the same sense on the smectic-C tilt cone and are separated from one another by 2\ensuremath{\pi} inversion walls. The dynamics of formation and the subsequent annealing of the foam have been probed using laser light scattering. Anisotropic coarsening of the foam, which is accounted for by including electrostatic (space-charge) interactions in the theoretical description of the ferr…

Efficient on-axis SLM engineering of optical vector modes

2020

Abstract This work presents a method for the efficient experimental generation of arbitrary polarized vector beam modes. The optical system employs two liquid-crystal on silicon (LCOS) spatial light modulators (SLM) in a common path architecture, avoiding the use of beam-splitters. Each SLM displays a different phase-only mask, each one encoding a different pattern onto two orthogonal linear polarization components of the input beam. These phase-only masks are designed using a recently proposed random technique to encode complex amplitude values. This encoding technique reconstructs the complex function on-axis, thus avoiding incorporating carrier phases. By addressing such properly designe…

Generalized formulation and symmetry properties of reciprocal nonabsorbing polarization devices: Application to liquid-crystal displays

2000

We present a general formulation based on the Jones-matrix theory for reciprocal nonabsorbing polarization devices, including polarization interference filters and liquid-crystal displays. The development of this formulation is based on general symmetry conditions that relate the Jones matrix when the device is illuminated from the front side and from the back side. The application to liquid-crystal displays results in a constraint of the Jones-matrix elements, which represents a generalization of the existing models that explain their modulation properties.

The physics and chemistry of liquid crystal devices, Gerald J. Sprokel, Ed., Plenum, New York, 1979, 348 pp. Price: $42.50

1981

Vector modes generation using efficient on-axis system

2020

Arbitrary polarized vector beam modes are efficiently generated. We use two flicker-free liquid-crystal on silicon (LCOS) spatial light modulators (SLM) in an on-axis common path architecture. Different superpositions of vector modes are obtained with high light efficiency.

Twist angle determination in liquid crystal displays by location of local adiabatic points

1998

In this work we present a method for the determination of the twist angle of an arbitrary twisted nematic liquid crystal spatial light modulator. The method is based on the location of local adiabatic points, i.e., situations in which the liquid crystal SLM acts only as a rotation device. For these cases, the rotation induced on the polarization of the incident beam is equal to the twist angle. Consequently, the twist angle can be determined with high precision. We show that local adiabatic regime may be achieved in two ways, either by changing the incident beam wavelength, or by applying a voltage to the electrodes of the display. However, the simple model that describes the SLM in the off…