Robert B. Meyer

Ferroelectric Liquid Crystals; A Review

Abstract The development and the current state of knowledge of ferroelectric liquid crystals are reviewed. Symmetry considerations first indicated that a ferroelectric phase should exist. Synthesis of new molecules led to the first experiments on electro-optical properties, indicating a spontaneous polarization. Various studies of bulk samples, including further electro-optical effects, shear induced polarization, pyroelectric effects, and switching experiments are discussed. Studies of the Curie point and effects visible in freely suspended films are summarized. Comparisons with crystalline ferroelectrics are made. Some further work and possible applications are indicated.

EFFECTS OF ELECTRIC AND MAGNETIC FIELDS ON THE STRUCTURE OF CHOLESTERIC LIQUID CRYSTALS

Electric or magnetic fields acting on the anisotropy of the electric or magnetic susceptibility exert torques within a liquid crystal which may compete with the elastic torques determining its internal structure. A general method is presented for calculating the structural changes thus produced. Two examples are given, and the field strength for the effects is estimated to be 105 V/cm or 105 G. Two experiments are suggested to test the theory.

On the existence of even indexed disclinations in nematic liquid crystals

Abstract The stability of cylindrically symmetrical line disclinations is examined by continum theory calculations and topological arguments, to show that these singularities can almost always be replaced by a continuous structure of lower energy. The calculations are applied to the four basic types of index ± 2 structures. Experimental observations are presented to support the proposed continuous structures as seen in cylindrical samples, and in the classical structures a fils and a noyaux.

Trigonometric Interpolation Method for One‐Dimensional Quantum‐Mechanical Problems

A rapidly converging difference method, based on harmonic analysis, is described. It can be applied to periodic or nonperiodic bound‐state problems of the general Sturm–Liouville type. Numerical examples for the Mathieu problem and for the harmonic oscillator show considerable accuracy. Advantages and disadvantages of the method are discussed in a comparison with Harriss matrix transformation technique and with direct integration methods. The set of difference equations representing a quantum‐mechanical problem constitutes a symmetric matrix eigenvalue problem which is approximately equivalent to the algebraic problem obtained by using a finite trigonometric basis. Basis functions associated with the difference method are related to the Dirichlet kernel. In an approximation which corresponds to the difference method, these basis functions can be treated in a similar way as Diracs δ function.

DISTORTION OF A CHOLESTERIC STRUCTURE BY A MAGNETIC FIELD

An experiment is described which confirms the theory of the distortion of a cholesteric structure by a magnetic field. Field effects in a sample of p‐azoxyanisole doped with cholesteryl acetate were viewed directly with a microscope, and the pitch of the helical structure was measured as a function of field strength.

Reconfigurable self-assembly through chiral control of interfacial tension

From determining the optical properties of simple molecular crystals to establishing the preferred handedness in highly complex vertebrates, molecular chirality profoundly influences the structural, mechanical and optical properties of both synthetic and biological matter on macroscopic length scales. In soft materials such as amphiphilic lipids and liquid crystals, the competition between local chiral interactions and global constraints imposed by the geometry of the self-assembled structures leads to frustration and the assembly of unique materials. An example of particular interest is smectic liquid crystals, where the two-dimensional layered geometry cannot support twist and chirality is consequently expelled to the edges in a manner analogous to the expulsion of a magnetic field from superconductors. Here we demonstrate a consequence of this geometric frustration that leads to a new design principle for the assembly of chiral molecules. Using a model system of colloidal membranes, we show that molecular chirality can control the interfacial tension, an important property of multi-component mixtures. This suggests an analogy between chiral twist, which is expelled to the edges of two-dimensional membranes, and amphiphilic surfactants, which are expelled to oil–water interfaces. As with surfactants, chiral control of interfacial tension drives the formation of many polymorphic assemblages such as twisted ribbons with linear and circular topologies, starfish membranes, and double and triple helices. Tuning molecular chirality in situ allows dynamical control of line tension, which powers polymorphic transitions between various chiral structures. These findings outline a general strategy for the assembly of reconfigurable chiral materials that can easily be moved, stretched, attached to one another and transformed between multiple conformational states, thus allowing precise assembly and nanosculpting of highly dynamical and designable materials with complex topologies.

Strain‐induced instability of monodomain smectic A and cholesteric liquid crystals

A mechanism is proposed for the observed mechanical instability of monodomain smectic A and cholesteric liquid crystals subjected to uniaxial dilative stress. The threshold conditions for the instability are derived, and the possible roles of dislocations in controlling the instability and in producing large plastic distortions are discussed.

Computations of the phase equilibrium, elastic constants, and viscosities of a hard‐rod nematic liquid crystal

Using an iterative solution to the Onsager integral equation for the orientational distribution function of spherocylinders in the nematic liquid crystal phase, we have studied several aspects of the Onsager theory of nematic ordering. We find that the isotropic–nematic coexistence region becomes narrower as the ionic strength of the solution decreases. We also calculate the curvature elastic constants and the nematodynamic viscosities of the nematic phase as a function of particle concentration. The results are compared to experimental data.

Point Disclinations at a Nematic-lsotropic Liquid Interface

Abstract The optical properties of a thin film of liquid crystal, with one of its surfaces bounded by the isotropic liquid of the same compound, reveal the existence of point defects in the liquid crystal. Particular sample geometries are examined in which the detailed structure of the optical patterns seen with polarized light can be analyzed to develop a qualitative picture of the structure of the liquid crystal layer near the defects. Changes in the optical pattern induced by an electric field are also analyzed. The observations indicate that the defects are point disclinations at the sirface of the liquid crystal, of the kind recently described by deGennes, rather than line disclinntions emerging from the liquid crystal.

Low temperature chiral nematic liquid crystals derived from β‐methylbutylaniline

The synthesis and some basic physical properties of three new liquid crystals are reported. Each of these compounds has been synthesized in both pure chiral and racemic versions. It is demonstrated that a mixture of the chiral and racemic versions of a compound produces a chiral nematic liquid crystal which behaves as a one component system in which the torsion of the helical structure varies linearly with composition, while other thermodynamic properties are independent of composition.