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Monte Carlo simulations are used to investigate the director configurations and the arrangements of the disclination lines that form in nematic shells surrounding interior spherical and polyhedral particles. For nematic shells formed around an interior spherical particle, a tetrahedral arrangement of the disclination lines is observed but this arrangement is lost if the interior sphere is shifted from the centre. The simulations indicate that a narrower angular distribution is observed for interior tetrahedral particles and, for non-centrosymmetric shells, the distribution is significantly less broadened compared to similar spherical inclusions. Other shape polyhedral particles are shown to give disclination geometries of different symmetries.

The topological properties of disclinations are quite different for liquid crystals in two dimensions (2D) or three dimensions (3D). In 2D, there are distinct types of disclinations with topological charges or winding numbers of any half-integer or integer. By contrast, in 3D, all half-integer disclinations are topologically equivalent to each other, and integer disclinations are not defects at all. In this study, we use numerical simulations to explore the crossover between 3D and 2D. We show that certain disclination lines between patterned surfaces can exist when the director field is free to rotate in 3D, but not when the director field is forced into the 2D plane (by an electric field applied to a liquid crystal with negative dielectric anisotropy). As a result, these disclinations are expelled from the liquid crystal.

We explore equilibrium structures and flow-driven deformations of nematic liquid crystals confined to 3D junctions of cylindrical micropores with homeotropic surface anchoring. The topological state of the nematic ordering field in such basic unit of porous networks is controlled by nematic orientation profiles in individual pores, anchoring frustration along the edges of joining pores and coupling to the material flow field. We numerically investigate formation of the flow-aligned configurations in single cylindrical pores and pore junctions. Depending on the arrangement of inlet and outlet flows in the junction, we demonstrate existence of numerous stationary nematic configurations, characterised by specific bulk defects and surface disclinations along joining edges. Observed bulk defects are nonsingular escaped structures, disclinations in the form of loops or disclination lines pinned to the joining edges of the pores. Furthermore, we show examples of defect dynamics during the flow-induced to...

We study two-dimensional equilibrium configurations of nematic liquid crystal (NLC) director in a cell bounded by two parallel surfaces. One surface is planar and the other one is spatially modulated. The relief of the modulated surface is described by a smooth periodic sine-like function. The orientation of NLC director easy axis is assumed to be homeotropic at one cell surface and planar at the other one. The NLC director anchoring with cell surfaces is assumed to be strong. We consider the case where disclination lines occur in the bulk of NLC above the extrema of the modulated surface. These disclination lines run along the crests and troughs of the surface relief. If the orientation of director at both bounding surfaces is of the same type, then NLC director field is continuous. For both configurations mentioned above (with defects and without defects), we obtain analytical expressions for director distribution in the bulk of NLC in the approximation of planar director deformations. Equilibri...

An electrically tunable liquid crystal (LC) lens with dual hole-patterned electrodes is demonstrated. When the LC lens is operated at low voltages, the dual hole-patterned electrodes with different diameters impart the lens with a coaxial bifocal characteristic. At high voltages, the proposed LC lens functions as a conventional lens with a single focal length but with a switchable optical aperture. The demonstrated LC lens is free of disclination lines because of the presence of voltage-assisted high pretilt angles created from the upmost hole-patterned electrode with small diameter.

Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 twist disclinations in a twisted nematic cell, using the two-dimensional finite-difference iterative method. We explore the biaxial structure of the defect core and describe its dynamics as the cell gap decreases. At a critical value of dc* ≈ 9ξ (here ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable, where the system starts to stretch the defect structure and the biaxiality starts to propagate inside of the cell. Compared to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of dc ≈ 7ξ, the system undergoes a biaxial transition, and the defect core merges into a biaxial wall with large biaxiality. This transition corresponds to the reconstruction of the nematic order already found in the bulk with no defect. The force reaches a maximum at d ≈...

Nematic liquid crystals (LCs) dropped via micro-dispenser (3 μL) on a vertical alignment (VA) polyimide coated indium tin oxide glass substrate have been observed under crossed polarisers. The wettability between the LC and the VA polyimide layer was extremely low. The contact angle of the LC droplet was around 33° and the droplet diameter was much smaller than the LC on the parallel-aligned polyimide layer. The contact angle of the droplet increased, and the droplet diameter decreased, on increasing the molar fraction of the side group of the polyimide. The flow behaviour of the LC by assembling between the two substrates has been directly observed under crossed polarisers. The droplet spread out keeping a cross-extinction pattern during assembling. After assembling to a 5 μm gap, a dark field was observed in whole area on the polyimide alignment layer with 50 mol% side group. Increasing the side group enhanced aligning the LC perpendicular to the substrate, and no disclination appeared.

We report experimental studies on defects in a nematic liquid crystal with negative dielectric anisotropy mounted in a cell with perfluoropolymer-coated surfaces. The sample exhibits a discontinuous anchoring transition from planar to homeotropic on cooling at zero or a small electric field, and above a cross-over voltage a continuous ‘inverse Freedericksz transition’, at which the director starts tilting in opposite directions at the two surfaces. Defects of strength ±1/2 are either annihilated or expelled when the director tilts. On the other hand, disclination lines of ±1 which end in partial point defects (boojums) at the surfaces in the planar alignment regime acquire point defects of strength ±1 at the midplane of the cell when the director tilts. At a low enough temperature, the homeotropic anchoring becomes strong, and an electric field above the Freedericksz threshold generates the usual umbilic defects, which follow the dynamic scaling laws found in earlier studies.

The thermal stability, alignment and electro-optic properties of liquid crystals can be fundamentally altered by dispersing small amounts of solid nanoparticles in a liquid crystal host. In the present study, the local alignment of the liquid crystal in such dispersions is studied by means of polarising optical microscopy and fluorescence confocal polarising microscopy. The results of two- and three-dimensional imaging indicate that birefringent stripes, which are induced by the presence of nanoparticles, correspond to twist disclinations that are located at the liquid crystal–substrate interface. The luminescence of dispersed semiconductor quantum dots shows that the ends of disclination threads are pinned to conglomerates of nanoparticles, which stabilise these line defects.

After an overview of cholesteric blue phases, we review our recent numerical studies on possible defect structures when blue phase I (BP I) is confined in a thin cell composed of two parallel surfaces imposing homeotropic anchoring. The cell thickness is of the order of the unit cell dimension of the bulk cubic BP I. We find several structures of disclination lines which, to our knowledge, have never been discussed in the field of liquid crystals as equilibrium structures. Those structures include a parallel array of double helix disclination lines, and two parallel arrays of undulating disclination lines almost (but not exactly) perpendicular to each other. A first-order transition between those two structures is possible, and the similarity between them is discussed.

The Peierls–Nabarro model, originally proposed to describe dislocation core in solids, is used to model core structures of 2π- and π-surface disclinations in the B2 phase of bent-shaped molecules. Structures of disclination cores are determined by surface anchoring. Core parameters as core widths (and positions of two partial π-disclinations as parts comprising 2π-disclination) are estimated using surface anchoring energy. Disclination core widths are usually narrow for strong anchoring. In such a case they are barely observable; nevertheless, they can exist.

A pathway for a coherent topological transition from the splay to bend director configuration in liquid crystal layers has been previously described via order reconstruction in a two‐dimensional sheet in the plane of the liquid crystal layer. In this paper we provide the details of the modelling of an alternative pathway that is based on the nucleation, motion and annihilation of an array of disclination lines. Electrical current flow onto the cell is calculated based on the two pathways and compared with data.

A novel method is described for the measurement of long pitch lengths in chiral nematic liquid crystals using the bowing of reverse twist disclination lines in 90° twisted nematic devices. The method has been used to measure pitch lengths of up to 50 mm, significantly longer than previously possible using existing methods. † The research was performed in part at the Department of Chemistry, The University of York, Heslington, York YO10 5DD, UK.

We have investigated the dynamics of pair annihilation of disclination lines in strong anchoring. This work is based on the Frank free energy. The director angle, φ(x, y, z), is obtained by the continuous theory. We show that the form of the viscous force in a confined nematic liquid crystal and in strong anchoring is a function of the initial distance between the two disclination lines. The asymptotic velocity, v asy, is also a function of the initial distance. Our theoretical result on the asymptotic velocity is in good agreement with previous experimental results.

A disclination is an orientation symmetry‐breaking defect and its strength corresponds to the number of rotations (in multiples of 2π) of the director over a path encircling the disclination. The line core plays a considerable role in the disclination energy balance and mobility, however, the detailed nature of the core structure is largely unknown. Here we demonstrate different core structures for different disclinations by using transmission electron microscopy and atomic force microscopy coupled with the nanostripe decoration technique. We show that the molecular distribution in the core of (+1) defects changes from the prolate planar to oblate homeotropic, resembling but not identical to ‘escape into the third dimension’. The homeotropic (−1) defect appears to possess an isotropic core, contrary to theoretical predictions.

The self-assembly of colloidal inclusions has recently been shown in smectic C* freely suspended films. In such 2D systems, the organization of the inclusions is qualitatively explained by elastic interactions induced by the disruption of the orientational order in the SmC* host phase. The interaction between resulting inclusion–defect pairs exhibits a dipolar character. We have developed a simplified model representing every inclusion and its companion hyperbolic defect by (+1)- and (−1)-wedge disclination lines, respectively. A finite anchoring energy has been introduced to explain the coalescence of the thinnest inclusions. Our model enables us to explain the chaining of the thickest inclusions and confirms the inclusion size dependence on the stability of the chains.

For a nematic polymethacrylate side chain liquid crystalline polymer, g 154 N 298 I (°C), the solidification-induced band texture has been observed aligned along the disclination under a polarizing optical microscope, when the specimen was quenched from 280°C to room temperature. The decoration technique of solidification-induced band texture, which is usually reported for main chain liquid crystalline polymers, was then introduced to reveal the director field pattern along a disclination for this side chain liquid crystalline polymer. It was found by infra-red dichroism measurements that the director orientation is parallel with the direction of the band. On this basis, disclinations with strength s=±1/2 and s=±1 were mapped according to the corresponding pattern of solidification-induced band texture. In addition, two types of inversion wall, loop-like and splay-type walls, were also found to be decorated by the solidification-induced band texture.

A new tensorial approach introducing unequal elastic constants in a two-dimensional lattice model is applied to simulate the influence of disclination interaction on the structures of half-wedge disclinations, for the understanding of the variation of apparent elastic anisotropy ϵ {\rm _{a}} measured from different disclinations in a texture (see preceding paper, part I [1]). The apparently random variation of ϵ {\rm _{a}} implies that disclination interaction has a strong effect on the structure of disclinations; as elastic anisotropy increases, its impact becomes overpowering. Nevertheless the disclination interaction still acts in the same way as in the case of equal elastic constants. Analysis of the free energy of disclination pairs shows that the structures of both +1/2 and −1/2 disclinations are changed under the influence of a neighbouring disclination, but in different ways. For +1/2 disclination, the splay and bend distortions vary with the relative orientation of its −1/2 neighbour. Meanwhile, ...

This work presents the effect of elastic anisotropy and disclination interaction on wedge disclinations in the nematic phase of thermotropic polymers, by combining experimental measurements, (this paper part I), with numerical simulation (part II [1]). In part I, the decoration provided by spontaneous banded texture gives much information about the defect structure of polymeric nematics. Working with a semi-rigid polyester, the optical images of +1/2 disclinations revealed by banding enable the distortion to be determined as a function of polar coordinates from the cores. Continuum theory allows the apparent elastic anisotropy, ϵ {\rm _{a}} , of bend and splay constants of the copolyester to be determined from the distortion measurement. The values of ϵ {\rm _{a}} , are seen to vary greatly in the range −1 to +1 between different +1/2 disclinations in the same sample. The statistics of the measurement indicate that the distribution of the values of ϵ {\rm _{a}} is random. The implication of these observat...

Two decoration methods, solidification-induced band texture decoration and focal-conic texture decoration, were established to map the director field of disclinations in a low molar mass methacrylate liquid crystal. It was found that when the specimen film is quenched from the nematic melt to room temperature, solidification-induced band texture is observed arrayed along with the schlieren texture, and the orientation of the director field can be displayed. Moreover, when the specimen is cooled from the nematic melt to 63°C and annealed, the focal-conic texture of the smectic A phase is found to grow around the corresponding disclination core with good orientation to reveal the director field. By the two decoration techniques, the director fields of disclinations with strength s = 1/2 and s = ± 1 were revealed. Two types of inversion wall, loop-like wall and splay-type wall, were found by both solidification-induced band texture decoration and focal-conic texture decoration.

The development of microstructure in nematic liquid crystalline polymers under shear flow is investigated through computational simulation. By using a tensorial expression for the elastic torque, the nemato-dynamic equation is numerically resolved. The simulation shows that elastic anisotropy has a strong influence on the evolution of the director and that the ‘log-rolling’ orientation of the directors emerges for tumbling nematics if the twist constant is smaller than the splay and the bend constants, even though one starts from a structure in which the directors are aligned within the velocity and velocity gradient plane. The interaction of wedge disclination pairs subject to a shear flow field is also simulated. The generation, multiplication and interaction of inversion wall defects during shearing have been revealed. In general the wall moves to the boundaries and is absorbed by the boundaries. When two walls of opposite orientation meet, a loop may form, then shrink, and finally collapse. Correspond...

One of the features of liquid crystalline polymers (LCPs) is their strong elastic anisotropy, which means they have unequal elastic constants. Elastic anisotropy plays a crucial role in the microstructure and macroscopic properties of LCPs. In this paper, the effect of unequal elastic constants on microstructure is investigated without an external field by using a deterministic tensorial approach. In this model, the evolution of the director field can be viewed as a process driven towards the state of zero elastic torque. A tensor expression of the elastic torque is used so that the nematic symmetry is automatically conserved. In simulations of bulk samples, disclination lines of strength half and escaped integer disclinations are observed. The distortion fields around the disclinations are found to depend on elastic anisotropy. If the twist constant is the lowest, as is the case for main chain liquid crystalline polymers, the disclination lines are predominantly of the twist type.

For a main chain thermotropic aromatic polyester with a flexible spacer, Cr 194 N 245 I (°C), the director fields around disclinations in the nematic mesophase can be decorated by both the solidification-induced band texture and surface microcracks. Director fields of various types of disclinations, including inversion walls, in the nematic mesophase of this semi-rigid polyester have been observed directly by polarizing optical microscopy. It was found that when the polymer was pre-sheared in the nematic state and then quenched to room temperature, a shear-induced band texture was observed, which relaxed slowly during annealing at 200°C, and then on quenching the solidification-induced band texture and surface microcracks appeared, displaying the pattern of the disclination fields. Pre-shearing is a necessary condition for the appearance of microcracks. On annealing, disclinations of various types were generated, quite often connected by inversion walls in the direction of pre-shearing. In some areas of t...

In this paper we employ a relatively simple theory to show how a nematic disclination line can act as a nucleation site for the growth of the isotropic phase. With this theory we are able to find analytical expressions for the critical temperature of nucleation and the behaviour of the core radius as a function of temperature. We are then able to compare these results with a previous numerical model of this effect.

We describe the director configurations associated with a negative dielectric anisotropy, high pretilt (typically ~ 85°) nematic cell. A number of distinct director configurations are observed, with both a transition to a spontaneously twisted state and a nucleated transition mediated by disclination line movement. We discuss the role of surface pretilt and elastic constant anisotropy on behaviour and give results on the relative energetic stability of the director states.

We describe an experimental situation with a looped line defect in nematic liquid crystals observed by polarizing optical microscopy. We measured the critical size of the loop below which it spontaneously shrinks and transforms into a point defect. The experiment was done with 5CB which gives rise to twist disclinations as do most of the usual nematics. For this kind of disclination an in-plane force due to the boundary conditions acts on the line and influences the critical radius. W e have constructed a model which is in good agreement with experimental measurements and deduced the line tension of the disclination.

We have measured the d.c. electric field dependence of the birefringence and conoscopic images for the smectic C* phase of a partially racemized ferroelectric chiral smectic liquid crystal CE-8. The experiments were performed using 50mu m thick homeotropic cells with lateral electrodes which created a d.c. electric field parallel to the smectic layers. The observed field induced birefringence shows a characteristic step-like behaviour which is due to the stepby-step unwinding of the helical structure in a sample with finite dimensions along the helical axis. In conoscopic observations we observe that these steps are associated with moving disclination lines that traverse the sample in the direction of the smectic layers. The observed electric field dependence of the birefringence is discussed in terms of the soliton-like unwinding of helical smectic structures and compared with the predictions of the Landau theory. A qualitatively good agreement is obtained.

Disclinations of high strength (S 1) in the hydrogen bond-induced nematic phases of p-alkoxycinnamic acids are reported. The existence of the disclinations of high strength is ascribed to the partial dissociation and regeneration of the hydrogen bonds in a mesastable equilibrium state around the clearing point and the core of the high strength disclination is an isotropic area.

The classical method for measuring the inherent periodicity, or “pitch”, in the order parameter in a cholesteric liquid crystal implies using a wedge cell with well‐defined boundary conditions. But the error can be large due to difficulties in controlling the wedge angle, α. A modified method is presented that significantly reduces the measurement error. A relief of indium tin oxide stripes on one of the plates shifts the disclination lines a distance proportional to both relief amplitude and to the wedge angle. With this “stripe–wedge Grandjean–Cano cell” the pitch can be accurately determined without a priori knowing α.

Mono-layers of stearic and behenic acids, deposited with the Langmuir-Blodgett technique, were used as aligning films in nematic liquid crystal cells. During the filling process the liquid crystal adopts a deformed quasi-planar alignment with splay-bend deformation and preferred orientation along the filling direction. This state is metastable and transforms with time into a homeotropic state once the flow has ceased. The transition is accompanied by formation of disclination lines which nucleate at the edges of the cell. The lifetime of the metastable splay-bend state was found to depend on the cell thickness. On heating, an anchoring transition from quasi-homeotropic to degenerate tilted alignment in the form of circular domains takes place near the transition to the isotropic phase. The anchoring transition is reversible with a small hysteresis.

We describe the experimental properties of metastable domains associated with the presence of an Inversion Wall (IW) and observed with homeotropically anchored nematic and cholesteric liquid crystals sandwiched between parallel glass plates. Such a distorted situation, stabilized by the application of an electric field parallel to the plates as described in reference [1], can also be obtained transiently either when filling a sample cell by capillarity or in some studies of directional solidification at the N-I interface [2]. The application of an electric field perpendicular to the plates with Delta epsilon 0 materials allows control of the reversal region thickness in the bulk of the sample and its associated birefringence. This IW can be stabilized in the particular case of low lateral extension globules in which the line tension of the looped disclination separating the pi wall regions from the homeotropic regions counterbalances the unfavourable bulk free energy. Particular attention is devoted to th...

A numerical technique has been developed to model texture in nematic liquid crystals. The technique differentiates between splay, twist and bend distortions and includes splay-splay compensation. The technique is tested by the simulation of the Freedericksz transition and by the determination of minimum energy director fields for specific boundary conditions. To model the bulk, periodic boundary conditions are imposed. The effect of elastic anisotropy on disclination character has been investigated by terminating simulations before all the defects have been annihilated. With a low twist constant, twist disclinations are observed; with a high twist constant, wedge disclinations are observed. With a low twist constant and high splay constant, realistic for polymeric liquid crystals, features observed experimentally are simulated.

In this paper the director configurations and the free energies of a nematic droplet with a surface normal anchoring condition are calculated numerically. For this surface anchoring, a transition occurs between the radial and axial structures with respect to an applied field. In the calculation of the director configurations, the position of a disclination has been fixed. Comparing the free energies for different disclinations, the stable position which gives the minimum free energy is found. In calculating the free energy of a droplet, it is assumed that the free energy density of the nematic phase does not exceed the isotropic free energy density, so that the large distortion in the vicinity of the disclination causes a nematic-isotropic transition and the free energy density of the disclination core becomes equal to the isotropic free energy density. The director configuration in a droplet is calculated as a function of an applied field for different isotropic free energy densities, elastic constant ra...

In order to describe the order director fluctuations in nematic liquid crystalline systems with inhomogeneous order parameter, the approach based on Frank elastic theory is extended by introducing spatially dependent rotational viscosity and elastic constants. Using the proposed model, eigenmodes of director fluctuations in the vicinity of a disclination line of strength 1 are examined. Particular attention is paid to the behaviour of fluctuations in the vicinity of the structural transition in a cylindrical cavity.

We report the first direct measurements of disclination density during shear flow of a nematic liquid crystal. Samples of 4,4′-n-pentylcyanobiphenyl, or 5CB, are initially aligned in the homeotropic configuration within a torsional shear cell using surface treatment with lecithin. For low shearing rates, the director rotates within the shearing plane, except near the axis of rotation where irregular time-dependent out-of-plane orientation patterns exist. Disclinations form above a threshold shear rate, with the first ‘thick’ and ‘thin’ disclinations appearing near the sample edge, rapidly multiplying, and subsequently filling the sample. We measure the steady-state disclination density, ρA, the length of disclinations per unit projection area. The dimensionless disclination density, ρA h, where h is the sample thickness, is found to depend on two dimensionless quantities: Er, the Erickson number, and [rtilde] = r/h, the scaled radial position. In the limit of large [rtilde]([rtilde]) 100), the de...

We examine the behaviour of nematic 4,4′-n-octylcyanobiphenyl (8CB) subjected to steady torsional shear flow at a temperature where this nematic is ‘tumbling’, i.e. the ratio α3/α2 of Leslie viscosities is negative. If the disc rotation speed is gradually increased from zero ( < 10−6 rad s−2), the director eventually departs from the shear plane and becomes oriented radially. However, if the disc rotation speed is increased from rest at higher rates, twist wall defects are created sequentially at the sample meniscus and propagate inward with velocity ≈0.85mm s−1. Eventually, disclinations are nucleated. Disclination density measurements reveal that over similar ranges of values of the Ericksen number Er, samples of 8CB have roughly ten times the disclination density of the flow-aligning nematic, 5CB, reported in the preceding paper. Additionally, a transition from a power-law exponent of 0.5 to 1.0 for the dependence of dimensionless disclination density on Er is observed near Er = 2000, consiste...

The nematic phase of the CsPFO/water system, when held in a cylindrical glass tube, spontaneously forms a detailed ‘cellular’ texture with an axial S = +1 disclination. This texture is the lyotropic discotic analogue of that previously found for a calamitic thermotropic system.

The isothermal annihilation kinetics of wedge disclinations in the fully liquid crystalline state were investigated using thin film specimens of a thermotropic liquid crystalline copolyester prepared by a solution-cast method. The as-cast films which are vitrified, homogeneous and amorphous were first subjected to a temperature jump to appropriate temperatures and the coarsening of the liquid crystalline texture was observed in real-time and in situ by means of optical microscopy and laser light scattering. The experimental results obtained show that, in the early stages, the domain size, D, which is inversely proportional to the square root of the density of disclinations in the sample, approximately obeys a power law of D(t) ∼ t 0.35 over the time scale covered in the experiment. In the later stages, anchoring of some of the disclination lines onto the glass surface and/or formation of crystallites from some sequences of the copolyester having a higher melting point suppress and then pin the an...

The full range of point defects of the type described by Poincarone is defined in terms of the disclination loop which would transform them into a monodomain. Calculations of energy of the points as a function of the defining angle, α, give the relative contributions of the splay, twist and bend components. Defects observed on fracture surfaces of a quenched liquid crystalline polymer are consistent with the point geometry predicted to have minimum splay distortion, and thus accountable for in terms of the high splay elastic constant characteristic of the polymeric nematic state.

Starting from the Landau-de Gennes free energy expression, the author has numerically analysed the director pattern in a nematic droplet of polymer dispersed liquid crystals. The nematic director has been understood as the eigenvector, which corresponds to the largest eigenvalue of the tensor order parameter. To investigate the droplet structure influence, all equations have been treated on the curvilinear coordinate system which is generated along the droplet boundary. In the case of spherical and spheroidal droplets with normal strong anchoring, the director exhibits an axial configuration and a disclination ring. The ring radius and the capactiance of the system change without hysteresis with the applied voltage.

The disclination strength defined on the boundary of textures generated by recently proposed simple modelling methods appears to be the sum of the strengths of primitive disclinations inside the boundary. In this paper, a rationalization is provided for these observations in two dimensions using an analytical expression for the conservation law for wedge type disclinations.

The transmission electron microscope technique enables direct visualization of disclination core structure of main chain liquid crystalline polymers. Generally, the lamellar structure, that is a function of type of polymer and molecular length, and of which the thickness is 10–200 nm, can be observed. In terms of distortions in the director field produced by a disclination, the elastic anisotropy, ∊, can easily be calculated. However, the ∊ does not indicate the molecular distortion produced by the disclination. Continuum mechanics is used to describe the relationship between the elastic anisotropy, ∊a, measured from the lamellar director and that, ∊b, of the molecular director in main chain liquid crystalline polymers. The relationship is ∊a = −∊b, indicating that lamellar distortion is completely different from the molecular distortion.

Surface tension is known to induce smectic O (SO) films at the free surface of isotropic droplets of 1-methylheptyl terephthalylidene-bis-4-aminocinnamate (MHTAC). The SO film has its molecules disposed in a herringbone fashion, with the layers parallel to the free surface. It constitutes a model of a 2D polar nematic liquid crystal without any contact to solid substrates. The film is oriented uniformly when applying a uniform electric field, except along disclination walls. By measuring the width of the disclination walls in the two configurations with the electric field parallel and perpendicular, we determine the anisotropy of the elastic constants in the induced So films. We find the ratio of the 2D bend to splay elastic constants K b/K s to be ≃ 0.25 which is anomalously small when compared to the corresponding 3D ratio (K 2 + K 3)/2K 1 usually found for the bulk nematic phase. This experimental result is comparable to measurements performed with 2D suspended Sc films with, however, a differ...