A general symmetry argument is presented, and experiments on newly synthesized p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate are described, demonstrating that chiral smectic C and H liquid crystals are ferroelectric. Some of the properties of this new class of ferro-electrics are discussed

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For experiments on chiral self-assembly, we used a two-component mixture consisting of 880 nm long rod-like fd viruses and the non-adsorbing polymer Dextran. In aqueous suspension, fd viruses alone exhibit purely repulsive interactions 13. Adding non-adsorbing polymer to a dilute isotropic suspension of fd rods induces attractive interactions via the depletion mechanism and leads to their condensation into colloidal membranes, equilibrium structures consisting of one-rod-length thick liquid-like monolayers of aligned rods (Fig. 1a) 11. Despite having different structures on molecular lengthscales, the longwavelength coarse-grained properties of colloidal membranes are identical to those of conventional lipid bilayers. However, unlike their amphiphilic counterparts, colloidal membranes do not form vesicles and are instead observed as freely suspended disks with exposed edges. Here, we investigate the behavior of these exposed edges in a manner analogous to previously studied liquid-liquid domains embedded in lipid bilayers [14][15][16] . For our experiments, it is essential that fd viruses are chiral, i.e. a pair of aligned viruses minimizes their interaction energy when they are slightly twisted in a preferred direction with respect to each other. The strength of chiral interactions can be continuously tuned to zero through either genetic or physical methods ( Supplementary Fig. 1) 13,17 .Before investigating chiral membranes, we determined the structure of a membrane's edge composed of simpler achiral rods using three complimentary imaging techniques, namely 2D and 3D polarization microscopy and electron microscopy. The local tilting of the rods within a membrane was determined using 2D LC-PolScope, which produces images in which the intensity of each pixel represents the local retardance of the membrane (Fig. 1d) 18. Such images can be quantitatively related to the tilting of the rods away from the layer normal, the z-axis 19. Rods in the bulk of a membrane are aligned along the zaxis, so that 2D LC-PolScope images appear black in that region (Fig. 1e). In contrast, the bright birefringent ring along the membrane's periphery reveals local tilting of the rods (Fig. 1e, Supplementary Fig. 2). For achiral rods, this indicates that a membrane has a hemi-toroidal curved edge (Fig. 1b, c). In comparison to an untilted edge, a curved edge structure lowers the area of the rod/polymer interface, thus reducing interfacial tension, at the cost of increasing the elastic energy due to twist distortion. This hypothesis is confirmed by visualizing the 3D membrane structure using electron tomography, whichshows that the viruses' long axis transitions from being parallel to the z-axis in the membrane bulk to perpendicular to the z-axis and tangent to the edge along the membrane periphery ( When viewed with optical microscopy, a membrane's edge exhibits significant thermal fluctuations, the analysis of which yields the line tension γ eff , the energetic cost required to move rods from the membrane interior to the periphe...

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Meyer et al} established the existence and behavior of ferroelectric liquid crystals. Since then many of the properties of these liquid crystals have been investigated: synthesis and properties of several compounds which have enhanced ferroelectric properties 2 " 4 ; optics and bulk properties 1 ; polarization and helical pitch 5 ; shear induced polarization 6 ; pyroelectricity 7 ; and fluctuations and domain walls in free smectic films. 8 Our experiment is a measurement of a new phenomenon:-the electroclinic effect (ECE)-and the critical behavior on the smectic-A side of the smectic-A-smectic-C phase transition. Although this effect is very closely related to piezoelectricity in crystalline phases, we use a distinctive name because the fluid nature of the liquid crystalline phase does not allow the static shear strains associated with piezoelectricity. This work is one of the first detailed studies of the critical properties of this phase transition. Our results raise some question about the exact nature of the phase change.A symmetry argument, similar to that predicting ferroelectricity in a chiral smectic-C , x describes the origin of the ECE in a smectie-A phase composed of chiral molecules. The application of an electric field parallel to the smectic layers of such a smectic-A biases the free rotation of the molecules and therefore produces a nonzero average of the transverse component of the molecular polarization. When such a dipole moment is present, a tilt of the long molecular axis (the director) is induced in a plane perpendicular to the dipole moment.In an aligned smectic-Asample, a tilt of the di-J. Low Temp. Phys. 23, 725 (1976). 10 For full details see G. Baym, C. J. Pethick, and M. Salomaa, to be published.rector is directly related to a tilt of the optic axis; therefore, the ECE results in a linear electro-optic response. The electro-optic effect manifests itself as a modulation of the birefringence. The ferroelectric smectic-A-smectic-C phase transition is second order and exhibits a divergence of the electric polarization susceptibility characteristic of a Curie point. 9 On the smectic-A side of the transition, a soft mode is observed for which the susceptibility A controlling tilt of the director goes to zero at the critical temperature T c according to a power law: A=a[(T-T c )/T c ]y.(1)Despite the striking resemblances to the crystalline ferroelectric Curie point, the phase change is driven by the intermolecular forces inducing the smectic-C phase and not by the spontaneous polarization which is a minor perturbation on these forces. In this sense, we consider the pretransitional behavior of the ECE to be a probe of the critical behavior near the smectic-A-smectic-C phase transition rather than a measure of the effects of dipole-dipole interactions. Because of the overall symmetry properties of the nonchiral smectic-A-smectic-C phase change, de Gennes has drawn an analogy between this transition and the normal-to-superfluid transition in 4 He where y cannot be directly measured. 10 In the hi...

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.

The specific magnetic-field-induced birefringence is measured in isotropic suspensions of the rodlike particle tobacco mosaic virus as a function of concentration and added salt. This quantity is proportional to the angular correlations between particles at zero field. In addition, the isotropic-nematic coexistence concentrations are measured as a function of ionic strength. The data compare well with a scaled functional theory assuming decoupling between the angular and spatial degrees of freedom.PACS numbers: 61.30. Gd, 61.25.Hq, 64.70.Md Liquid crystals composed of particles interacting with only repulsive potentials are important for fundamental, practical, and biological reasons. First, the study of simple liquids has shown that repulsive forces largely determine the structure of liquids and that attractive potentials can be successfully treated perturbatively. Thus hard-rod liquid crystals may serve as a reference state to study thermotropics. Indeed, recent Monte Carlo simulations have demonstrated that hard-core liquid crystals exhibit a smectic phase similar to thermotropics. 1 Second, hard-core liquid crystals of large length-todiameter (aspect) ratio approximate main chain polymer liquid crystals which have found applications, for example, in the production of high-strength fibers. Third, aligned charged filaments with liquid-crystalline properties such as muscle fibers and retinal cells play important roles in the biological milieu.The first microscopic theory for the isotropic-tonematic (/-TV) phase transition in a hard-rod system was developed by Onsager. 2 It predicts that a dilute suspension of very anisotropic, hard, rigid rods forms an orientationally ordered (nematic) phase at a critical volume fraction which depends only on the aspect ratio of the rods. Onsager considered two-body interactions which limits the theory to particles with an aspect ratio greater than about 100. However, it is expected that shorter hard rods also form nematic phases since three-body interactions act to stabilize the nematic phase. 3 ' 4 While suspensions of hard, rigid rods are interesting theoretically they do not occur in nature and such rods are difficult to synthesize. On the other hand, charged rods are abundant in nature and similarly to hard particles, interact with a pair potential dominated by repulsion. The effect of charge is twofold. First, at a given ionic strength it has been argued that the free energy of the electrostatic repulsion between particles is equivalent to increasing the diameter of the particle by the distance at which the interparticle repulsive potential falls to a value of about kT. 25 Second, the angular-dependent electrostatic potential between two like charged cylinders acts to misalign the particles and its magnitude is characterized by the "twist" parameter h. 5 Tobacco mosaic virus (TMV) is in many ways a model rigid charged rod. TMV suspensions in water can be made monodisperse through careful preparation. Viewed at low resolution in an electron microscope, TMV appears as a r...

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