We report a liquid crystal smart reflector, consisting of a cholesteric liquid crystal doped with dye. Light entering the liquid crystal is absorbed by the dye, generating heat which raises the average temperature of the liquid crystal. This in turn changes the pitch length of the cholesteric liquid crystal, causing an increase in its reflectivity, and thus reducing the amount of light absorbed by the dye molecules. A negative feedback stabilized condition is reached, in which the reflectivity is proportional to the incident light intensity. This effect is demonstrated both theoretically and experimentally.

In free standing films of one smectic C* material, Chisso 1015, we observe circular islands, of greater thickness than the background film. These islands, nucleated by smoke particles, grow to an equilibrium diameter that is a function of their thickness. We present data on island size, and a theory attributing the finite equilibrium size to a negative island edge energy arising from a spontaneous bend term in the elastic free energy for the islands. We also observe textural transformations within the islands, attributed to a difference between splay and bend elastic constants, combined with weak anchoring of the director at a point disclination at the center of an island.

We report on an electro-optical study of a liquid-crystal-polymer composite system. This system is made by dissolving a small amount of acrylate monomers (8%) plus crosslinkers in a nematic liquid crystal, and then photopolymerizing the homogeneous mixture. These nematic gels show properties different from those of ordinary nematics or polymer stabilized liquid crystals. By studying the electric field induced Frederiks transition, some basic propel-ties of the nematic gels can be deduced. We compare the experimental results to a simple phenomenological model of the nematic gel, involving a characteristic length scale of order 1 mu m, which is also visible as speckles, an effective internal aligning field of a few statvolts per cm, and an increased rotational viscosity on the order of 10(4) P. We indicate how a microscopic model might relate the first two of these parameters.

We report a piezoelectric effect in cholesteric liquid crystalline elastomer gels. When we apply a shear stress to a cholesteric elastomer gel in the direction perpendicular to its helical axis, a polarization can be induced in the direction perpendicular to both the stress and the helix. This experimental observation agrees with the theory proposed by Pelcovits and Meyer [J. Phys. II France 5, 877 (1995)].

An important approach to understanding phase transitions in liquid crystals is to study systems in which the dominant interparticle interactions are hard repulsion, rather than the complicated interparticle potentials found in most liquid crystals. Computer simulations have shown [1] that a nematic to smectic A phase transition may exist in a system as simple as monodisperse hard rods. Experimentally, Xin Wen, Robert Meyer and Donald Caspar [2] have reported the observation of the smectic A ordering in tobacco mosaic virus (TMV) suspensions, in which the dominant interparticle interactions are screened electrostatic repulsion. In this paper we present the first quantitative measurements of the nature of the nematic to smectic A phase transition in TMV. In solutions in which the concentration is just below the transition concentration to the smectic phase, large pretransitional smectic fluctuations are observed. We will describe the methods of measuring the correlation lengths of these presmectic fluctuations by light scattering. In addition, the concentration difference between the smectic and the nematic phase close to the transition point is determined to be very small, implying that the transition is very close to second order. This result is consistent with the conclusion of numerous theoretical approaches [3], such as density functional theory and scale particle theory, which have concluded that a nematic to smectic A transition in a system of rigid rods should be second order or very close to second order.

We have discovered spiral formation in nematic liquid crystal solitons under the influence of a rotating magnetic field. The shape of the spirals is well modeled by a rotating spiral of Archimedes, except in the immediate vicinity of the cores. The rotation of the driving magnetic field breaks the symmetry between counter rotating spirals, leading to differing wavelengths and spiral rotation rates. As the magnetic field rotation rate is decreased below a critical value, the wavelength diverges while the spiral rotation rate drops to zero. This divergence is related to a structural transition occurring within the solitons themselves. The spirals can be understood by examining the topology and symmetries of the solitons.

A multipass tandem Fabry–Perot interferometer was used to measure the Brillouin light scattering in nematic polymer solutions of poly-γ-benzyl glutamate (PBG). The longitudinal acoustic phonon frequency and linewidth were determined as a function of the angle between the phonon wave vector and the nematic director. We have observed an anisotropy of 22% in sound velocity and 40% in the Brillouin linewidth in PBG nematic solutions. Our analysis indicates that elastic relaxation due to polymer concentration fluctuations is important. However, the proposed second sound wave could not be determined due to the experimental limit of the present technique.

The static and dynamic properties of the flexoelectric effect in cholesteric liquid crystals are presented. In a simple geometry, the application of an external electric field perpendicular to the cholesteric helix results in a linear electro-optic effect. The switching time for optical modulation is almost independent of the field strength. The temperature dependence of this optical switching follows the Arrhenius type behavior.

We report the discovery of a novel, magnetic-field-driven first-order phase transition in nematic liquid crystals. The transition is between a spatially periodic distortion, stable at intermediate field strengths, and a uniform distortion which is the ground state at high fields. From studies of dynamics we show that the transition is first order. We also find a spinodal point, below which the transition from the uniform to the periodic state occurs continuously. We discuss the utility of thickness gradient samples and determine the equilibrium wavelength of the periodic phase as a function of magnetic-field strength.

We have designed and built a light scattering system that can detect scattered light in two spherical angles with scanning ranges more than 270° about the vertical axis and 100° about a horizontal axis. The detector and the sample holder are automated by high-precision stepping motors with a minimal angular increment 0.01° or 0.02°. A novel modular design in the detector allows the experimenter to examine the image of the scattering object and the direction of the scattered light while the detector is fixed at the measurement position. The angular resolution of the system is smaller than 0.19° in both azimuthal and polar directions. This setup has been successfully applied to study the static and dynamic properties of the ordered phases in colloidal solutions.

The static and dynamic properties of the flexoelectric effect in cholesteric liquid crystals are presented. The application of an external electric field, below the critical strength for helix unwinding, perpendicular to the cholesteric helix, results in a linear electro-optic effect. The experimental results are in good agreement with theoretical predictions made under the assumption of the uniform distortion of the helix due to the flexoelectric coupling with the field. The temperature dependence of the dynamic response to the field is found to be the Arrhenius type. It is suggested that the surface boundary conditions play a role in the properties of the flexoelectric effect.

We report the first systematic measurements of elastic coefficients and viscosities that clearly demonstrate the distinction between rigid and semiflexible behaviour of a main-chain polymer nematic liquid crystal, a solution of poly-γ-benzyl glutamate (PBG) in mixed organic solvents. Quasi-elastic Rayleigh scattering studies show a crossover which occurs at a molecular chain length near the persistence length of PBG as the chain length increases. The results are in qualitatively good agreement with recent theoretical predictions for semiflexible chains. It is seen that bending distortions of an individual polymer play an important role in the fundamental nature of nematic elasticity and viscosity.

We have observed the growth of highly ordered textures in homogeneously aligned poly(γ-benzyl-glutamate) (PBG) liquid crystals as the polymer concentration increases. The textures are similar to the hexagonal columnar textures exhibited by recent studies on highly concentrated solutions of helical biological polymers. In a geometry of homeotropic alignment, no evidence of such texture growth was seen, which is probably due to strong binding interactions between PBG polymers and the substrates.

Suspensions of Tobacco Mosaic Virus in water have a remarkable phase diagram exhibiting a number of ordered states. To some extent the ordering can be understood in terms of hard particle interactions, which makes the variety of ordered states all the more remarkable. This article discusses our current knowledge of the Tobacco Mosaic Virus system, some ideas about the types of order observed, and the possibilities for future research.

We first discuss the progress in linear optics, in particular, the formulation and application of geometrical-optics approximation and its generalization. We then discuss the progress in non-linear optics, in particular, the enhancement of a first-order Freedericksz transition and intrinsic optical bistability in homeotropic and parallel oriented nematic liquid crystal cells. Finally, we discuss the liquid crystal alignment and surface effects on field-induced Freedericksz transition. 50 refs.

We present experimental evidence of the smectic-A (${S}_{A}$) phase in colloidal solutions of tobacco mosaic virus. The smectic-A phase is determined by the observation of a layered structure along the virus alignment direction and a liquidlike order within layers. In our samples, we also observed the characteristic ${S}_{A}$-type focal conic textures and in-layer undulational fluctuations. Our observations confirm the predictions from computer simulations and theory of smectic-A order in the system of hard rods.

Dilute suspensions of micron diameter dielectric spheres confined to two dimensions are induced to aggregate linearly by application of an electric field. The growth of the average cluster size agrees well with the Smoluchowski equation, but the evolution of the measured cluster size distribution exhibits significant departures from theory at large times due to the formation of long linear clusters which effectively partition space into isolated one-dimensional strips.