Showing papers on "Liquid crystal published in 1976"

Introduction to Liquid Crystals

Abstract: 1 Liquid Crystal Mesophases.- 1. Mesophases.- 1.1 Disordered Crystal Mesophases.- 1.2 Ordered Fluid Mesophases.- 2. Types of Liquid Crystals.- 2.1 Thermotropic Liquid Crystals.- 2.2 Lyotropic Liquid Crystals.- 3. Classification According to Molecular Order.- 3.1 Nematic Order.- 3.2 Cholesteric Order.- 3.3 Smectic Order.- 4. Polymorphism in Thermotropic Liquid Crystals.- 5. Molecular Structure of Thermotropic Mesogens.- 6. Properties of Ordered Fluid Mesophases.- 2 Structure-Property Relationships in Thermotropic Organic Liquid Crystals.- 1. Introduction.- 2. Organic Mesophases.- 3. General Structural Features of Mesogens.- 4. Effects of Structure on Mesophase Thermal Stability.- 5. Homologous Series.- 6. Materials for Device Applications.- 7. Summary.- 3 Introduction to the Molecular Theory of Nematic Liquid Crystals.- 1. Introduction.- 2. Symmetry and the Order Parameter.- 3. The Molecular Potential.- 4. The Orientational Distribution function.- 5. Thermodynamics of the Nematic Phase.- 6. Fluctuations at Tc.- 4 Generalized Mean Field Theory of Nematic Liquid Crystals.- 1. Introduction.- 2. The Pair Interaction Potential.- 3. The Mean Field Approximation.- 4. Statistical Thermodynamics.- 5. Nature of the Parameters UL.- 6. The Need for Higher Order Terms in V1.- 5 Hard Rod Model of the Nematic-Isotropic Phase Transition.- 1. Introduction.- 2. Derivation of Onsager Equations.- 3. Solution of Onsager Equations in a Simplified Case.- 6 Nematic Order: The Long Range Orientational Distribution Function.- 1. Introduction.- 2. The Orientational Distribution function.- 3. Macroscopic Definition of Nematic Order.- 4. Relationship Between Microscopic and Macroscopic Order Parameters.- 5. Experimental Measurements.- 5.1 Measurements of ?P2(cos ?)? Based on Macroscopic Anisotropies.- 5.2 Measurements of ?P2(cos ?)? Based on Microscopic Anisotropies.- 6. Experimental Data.- 7 Introduction to the Molecular Theory of Smectic-A Liquid Crystals.- 1. Introduction.- 2. Symmetry, Structure and Order Parameters.- 3. Phase Diagrams.- 4. The Molecular Potential.- 5. Statistical Thermodynamics.- 6. Numerical Results.- 7. Improved Theory.- 8. The Possibility of Second-Order Transitions.- 8 Introduction to the Elastic Continuum Theory of Liquid Crystals.- 1. Introduction.- 2. The Fundamental Equation of the Continuum Theory of Liquid Crystals.- 3. Applications of the Elastic Continuum Theory.- 3.1 Twisted Nematic Cell.- 3.2 Magnetic Coherence Length.- 3.3 Freedericksz Transition.- 3.4 Field-Induced Cholesteric-Nematic Transition.- 4. Concluding Remarks.- 9 Electrohydrodynamic Instabilities in Nematic Liquid Crystals.- 1. Introduction.- 2. Nature of the Instability and the Balance of Forces.- 3. Dielectric Response.- 4. Hydrodynamic Effects.- 5. The Boundary Value Problem in the Conduction Regime.- 6. The Torque Balance Equation.- 7. Numerical Results and Comparison with Experiment.- 8. Range of Applicability.- 10 The Landau-de Gennes Theory of Liquid Crystal Phase Transitions.- 1. Introduction.- 2. Derivation of the Fundamental Equations of the Landau-de Gennes Theory.- 2.1 The Partition function.- 2.2 The Landau Expansion.- 2.3 Generalization of the Landau Expansion to Liquid Crystals.- 3. Thermodynamic Properties of Liquid Crystal Phase Transitions.- 4. Fluctuation Phenomena.- 4.1 Homophase Fluctuations in the Isotropic Phase.- 4.2 Heterophase Fluctuations.- 5. Observation of Fluctuations Using Light Scattering.- 6. Magnetic Birefringence and the Paranematic Susceptibility.- Appendix A.- Appendix B.- 11 Introduction to the Optical Properties of Cholesteric and Chiral Nematic Liquid Crystals.- 1. Introduction.- 2. Maxwell's Equations.- 3. Discussion.- 4. Conclusion.- Appendix A.- Appendix B.- 12 Liquid-Crystal Displays-Packaging and Surface Treatments.- 1. Introduction.- 2. Packaging.- 3. Electrodes.- 4. Surface Orientation.- 5. Influence of Packaging on Surface Orientation.- 6. Summary.- 13 Pressure Effects in Sealed Liquid-Crystal Cells.- 1. Introduction.- 2. Effect of Temperature Change.- 3. Effect of Glass Thickness.- 4. The Case of a Rigid Container.- 14 Liquid-Crystal Displays-Electro-optic Effects and Addressing Techniques.- 1. Introduction.- 2. Electro-optic Phenomena.- 2.1 Field-Induced Birefringence.- 2.2 Twisted Nematic Effect.- 2.3 Guest-Host Effect.- 2.4 Cholesteric-to-Nematic Transition.- 2.5 Dynamic Scattering.- 2.6 Storage Mode.- 2.7 Transient Response.- 3. Display-Related Parameters.- 3.1 Display Life.- 3.2 Temperature Dependence.- 4. Addressing Techniques.- 4.1 Matrix Addressing.- 4.2 Beam Scanning.- 5. Summary.- 15 Liquid-Crystal Optical Waveguides.- 1. Introduction.- 2. Guided Optical Waves.- 3. Phase Matching and Coupling.- 4. Scattering.- 5. Liquid Crystal Waveguides.- 6. Conclusions.- 16 The Electro-optic Transfer Function in Nematic Liquids.- 1. Introduction.- 2. Geometrical Considerations in Optical Measurements.- 3. Field Effects-Negative Dielectric Anisotropy.- 4. Field Effects-Positive Dielectric Anisotropy.- 5. Hydrodynamic Effects-Diffraction by Domains.- 6. Dynamic Scattering.- 7. Photoconductor Control.- 17 Electrochemistry in Nematic Liquid-Crystal Solvents.- 1. Introduction.- 2. Equilibrium Properties of Bulk Solutions.- 3. Electrochemical Reactions.- 18 Lyotropic Liquid Crystals and Biological Membranes: The Crucial Role of Water.- 1. Introduction.- 2. Lyotropic Liquid Crystals.- 2.1 Constituents of Lyotropics.- 2.2 Micelles.- 2.3 Structure of Lyotropics.- 3. Biological Membranes.- 3.1 Constituents of Membranes.- 3.2 Structures of Membranes.- 4. Interaction of Amphiphilic Compounds with Water.- 4.1 Solubility of Hydrocarbons in Water.- 4.2 Solubility of Ionized Species in Water.- 4.3 Aggregation of Amphiphilic Compounds.- 5. Conclusion.

Liquid crystal devices

Abstract: A liquid crystal device includes a sheet of plastic material having an open pore structure in which a liquid crystal material has been introduced. The liquid crystal material may be dichroic and contain one or more dyes which may be dichroic. The liquid crystal material may be nematic or cholesteric or a mixture of these two or a smectic material. Protective layers of plastic or glass may be arranged to enclose the sheet and the protective layer may carry electrodes. The liquid crystal may be applied to selected portions only of the sheet and the remaining parts of the sheet filled with a non-mesomorphic material.

Liquid Crystalline Structure In Aqueous Hydroxypropyl Cellulose Solutions

Abstract: Concentrated aqueous solutions of hydroxypropyl cellulose form lyotropic mesophases displaying a range of iridescent colors. Evidence from light microscopy and optical rotatory dispersion suggests that the mesophase has helicoidal structure, resembling in some respects that of cholesteric liquid crystals.

Elastic and Optical Properties of Some 4′-n-Alkyl-4-Cyanobiphenyls

Abstract: The bend elastic constants (k 33) and order parameters (S) derived from optical measurements in the nematic phase of pentlyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) are reported. The odd-even effect is clearly seen in the K 33 values of all four compounds and in the S values of the first three. 5CB, 6CB and 7CB show only the nematic mesophase but their elastic constants indicate the existence of smectic-like short range order. For example, even the lowest homologue, 5CB, does not obey the law k 33 ∞ S 2 given by the mean field throry. 7CB, has about the same order parameter as 5CB but a much higher elastic constant. 8CB, which shows a smectic A phase as well, exhibits a lower k 33 than 7CB near the nematic-isotropic transition point but a pronounced pretransitional increase near the A-N transition.

Theory of piezoelectricity in nematic liquid crystals, and of the cholesteric ordering

Abstract: A statistical-mechanical theory of the elastic constants of a liquid crystal based on the Onsager expansion is reexamined, with emphasis on the terms linear in the gradients of the director. This gives a microscopic theory of the piezoelectric effect in nematic liquid crystals, and of the spontaneous twisting of a cholesteric. Model cases of tapered rods, bent rods, and threaded rods are considered.

Method of manufacture of liquid crystal displays

Abstract: A liquid crystal display assembly including a plurality of individual liquid crystal displays formed on a pair of cooperating substrates with the displays isolated from one another by a sealing pattern served to define individual displays. One method of forming a plurality of liquid crystal displays includes the steps of applying a conductive pattern to one surface each of a pair of substrates, the pattern cooperating when the substrates are face to face to form the plurality of displays, providing sealing means on at least one of the surfaces prior to bringing said surfaces together and in a pattern isolating each of the plurality of displays to form a plurality of displays cells, filling the cells with liquid crystal material, sealing the cells by bringing the substrates together and cutting substrates to form the displays.

Surfactant association structure and emulsion stability

Abstract: Recent results on the concentration dependence of the mutual interaction between dodecyl sulphate and dodecanol in emulsions were used as a basis to demonstrate the necessity of taking water/ emulsifier interaction into account when interpreting the enhanced stabilizing action of combined emulsifiers. The usefulness of three-dimensional association structures, such as liquid crystals, as model substances for obtaining information about the structure and bonding conditions of combined emulsifiers at an interface, was discussed. The earlier opinion on the presence and location of lyotropic liquid crystals in emulsion systems was verified by optical and electron microscopy and the structure of the phases identified by low-angle X-ray diffractometry. The influence of the presence of liquid crystals at the o/w interface on the flocculation and coalescence of emulsion droplets was estimated from the change in van der Waals (VdW) interaction. The results indicated a negligible influence of the changed attraction on the flocculation process from the adsorption of liquid crystals at the interface. On the other hand, the corresponding effect on the coalescence was pronounced; the presence of a liquid crystal reduced the VdW energy available for bringing about coalescence, by a factor of about 20.

The Determination of the Elastic Constants of Nematic Liquid Crystals

Abstract: The elastic constants K11 and K33 are calculated from the threshold field He associated with the Frederiks transition in a magnetic field of a uniform planar and a horneotropic layer, respectively. The elastic constant K22 is determined indirectly using a twisted planar layer.The errors associated with the determination of Hc are critically evaluated. In particular the anchoring conditions at the boundaries are found to have an important influence on Hc. Results for all three elastic constants of PAA and MBBA are given. In general our values for K11 and K33 are substantially higher than those reported in the literature.

Surface defects and structural transitions in very low anchoring energy nematic thin films

Abstract: It has been discovered that the products of degradation of heated paper evaporated on glass constitute a low anchoring energy substrate for the nematic phase of MBBA (methoxy benzylidene butylaniline). The extrapolation length b=K/2Ws is of the order of 100 μm. In very thin specimens the anchoring is conical at low temperatures and becomes homeotropic at higher temperatures. A transition to (ordinary) strong anchoring conditions appears at still higher temperatures, presumably due to the appearance of a slight isotropic layer of MBBA at the interface. We have been interested in the study of defects typical of the weak anchoring phases, in specimens thinner than b. One observes the existence of Bloch walls. This typical defect allows for a direct measurement of the surface anchoring energy (Ws ∼ 10−4 erg/m2). Other defects are nuclei of strength ±1 (in repulsive or attractive interaction with the walls according to whether they are +1 or −1 nuclei), and reversing points which separate Bloch wall segments o...

Synthesis and Liquid Crystal Properties of Chiral Alkyl-Cyano-Biphenyls (and -p-Terphenyls) and of Some Related Chiral Compounds Derived from Biphenyl

Abstract: Using only (-)-2-methylbutan-1-ol as an optically active starting material, other chiral aliphatic materials have been derived by synthetic procedures which preserve the optical activity, and a num...

Analysis of weak-boundary-coupling effects in liquid-crystal displays

Abstract: The analysis of Rapini and Papoular for homeotropic and homogeneous geometries is extended to predict the effects of weak boundary coupling on liquid-crystal display performance. An implicit expression for deformation as a function of applied field is derived for the case of equal elastic constants. Steeper transitions with complete saturation at low fields are found, which promise improved optical performance and multiplexing capability. A similar analysis of twisted nematic displays predicts a less pronounced improvement in electro-optic response and indicates a minimum boundary-coupling strength below which spontaneous deformation occurs.

The Relationship Between Helical Twist Sense, Absolute Configuration and Molecular Structure for Non-Sterol Cholesteric Liquid Crystals

Abstract: The helical rotary senses for a number of non-sterol cholesteric liquid crystals have been determined and from the results, a simple rule relating molecular structure, absolute configuration and twist sense is proposed. The rule has been used to predict correctly the helical twist senses for some new cholesterogens.

Flexoelectricity in nematic and smectic-A liquid crystals

Abstract: Flexoelectric effects are observed in both the nematic and smectic‐A phases of p‐butoxybenzal‐p‐ (β‐methylbutyl) aniline (BBMBA) and p‐cyano‐benzylidine‐p‐octyloxyaniline (CBOOA). This is the first reported observation of flexoelectricity in smectic phases. The use of a symmetric interdigital electrode in the homeotropic geometry facilitated the unambiguous separation of linear and quadratic electro‐optic effects. Both the interdigital electrodes and those liquid‐crystal deformations that are quadratic in the voltage act as optical diffraction gratings with a spacing that corresponds to the repeat distance d for adjacent electrodes. In contrast linear electro‐optic effects give rise to diffraction gratings with twice this spacing since adjacent electrodes have opposite voltages. Diffraction maxima due to the linear effects are halfway between the maxima due to the other effects. Using optical heterodyne detection, the intensity of the diffraction maxima believed to arise from the linear effect are indeed ...

Refractive Indices and Optical Anisotropy of Homologous Liquid Crystals

Abstract: We have measured as functions of temperature the refractive indices and linear birefringence of seven homologous compounds of p, [pacute]-di-n-alkoxy-azoxybenzenes in the nematic phase. Using the Vuks' model of local-field correction, we have deduced from our results both the microscopic and the macroscopic order parameters. The former agree well with those determined by Pines et al from the NMR results. The variations of the various microscopic parameters with the increase of the alkyl chain length are discussed. It is shown that addition of CH2 groups to the alkyl chain increases the average polarizability much faster than the polarizability anisotropy. Contributions to the polarizability anisotropy from the core and from the alkyl chains respectively are found.

Pre-and Post-Transitional Behavior of the Flow Alignment and Flow-Induced Phase Transition in Liquid Crystals

Abstract: Abstract The flow alignment in the isotropic and nematic phases of a liquid crystal is studied theoretically with special emphasis on temperatures close to the transition temperature. The point of departure is a nonlinear, inhomogeneous relaxation equation for the alignment tensor which is applicable to both phases. The stationary solutions of this equation are analysed. In addition to some well-known results which are recovered as limiting cases for small velocity gradients, it is found that a sufficiently large velocity gradient can induce a transition into an ordered phase if the temperature is between the transition temperature for equilibrium conditions and a somewhat larger critical temperature. In the nematic phase, a weak dependence of the flow alignment angle on the magnitude of the velocity gradient is obtained. The relaxation towards a steady state is also considered.

Dielectric and optical studies of a nematogen (4,4-n-heptyl-cyanobiphenyl)

Abstract: The permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions. The anisotropy of molecular polarizability is less than in benzene. Kirkwood–Bordewijk g-factors show significant dipole antiparallelism in the isotropic and nematic phases: in the latter it is much larger parallel to the director axis than perpendicular to it. The two major (orthogonal) component activation enthalpy and entropy terms for dipole reorientation (Bauer) in the nematic phase (including benzene solutions) are compared with those in the isotropic media: in the pure nematic ΔHB(‖)= 60 ± 8 kJ mol–1; ΔHB(⊥)= 6 ± 2 kJ mol–1. The current theoretical representations of the nematic phase are examined using the experimental data. The occurrence of pre-transitional molecular interaction in benzene solutions (above 3 mol dm–3) and in the pure isotropic phase can be detected.

Effects of Molecular Size and Shape in Solution Thermodynamics

Abstract: The one-fluid corresponding states theory is used to predict excess thermodynamic quantities of a mixture of spherical molecules of different e and σ. Two prescriptions of ‘van der Waals type’, and a third used by Flory, give the parameters e m and σ m of the solution. Comparison of the results is made with Monte Carlo calculations of Singer and Singer and the Snider–Herrington theory, and also with experimental features of simple and polyatomic spherical molecule mixtures. For each prescription an intuitive discussion is given of contributions to the excess quantities arising from (a) the energetic weakness of (1–2) contacts relative to (1–1) and (2–2) and (b) dissimilarity of free volume between the components. Two free volume contributions are distinguished. One depends on the second derivative with respect to T of the energy, volume, etc. of the reference liquid. The other occurs only in V E where it is of major importance and depends on d V /d T and a dissimilarity of molecular energy/volume parameters of the components. Recent experiments indicate two effects outside current theory. For systems containing anisotropic molecules, there is a third contribution to excess quantities (c), due to short-range orientational order or correlations of molecular orientations in one or both components. Mixing liquids of differing degrees of order usually brings about a net decrease of order, and hence positive contributions in Δ H M and Δ S M . The effect is illustrated by Δ H M values of branched and normal alkane mixtures at 25°, the temperature dependence of Δ H M for such systems, and the widely different. Δ H M of cis and trans dimethylcyclohexanes mixed with the orientationally ordered n -C 16 . The properties of systems containing a nematic liquid crystal (MBBA) and an alkane are sensitive to the alkane shape and indicate that MBBA molecules correlate their orientations with normal, but not with highly branched alkanes. The fourth contribution (d) is seen in systems involving alkanes of the same molecular shape but different degrees of steric hindrance of torsional oscillations. Heats of mixing point to a thermodynamic effect associated with a coupling of the molecular motions of the components.

A molecular‐statistical theory of the temperature‐dependent pitch in cholesteric liquid crystals

Abstract: An interaction between chiral molecules is derived in terms of the orientations of their long molecular principal axes. In analogy with Maier–Saupe and Goossens the derivation is based on the electric multipole expansion. The molecules are assumed to behave as if they were cylindrically symmetric, i.e., the system is locally nematic. As an example the chiral molecules are represented by Kuhn models, and the relevant coupling constants are calculated explicitely. An expression for the free energy is obtained in the molecular field approximation. It is shown that, if only the induced dipole–dipole and the dipole–quadrupole dispersion energies are taken into account, a temperature‐independent cholesteric pitch is obtained. This result is traced back to the symmetric character of the interaction. In order to explain the experimental situation one has to introduce, in analogy with Keating, an asymmetry producing interaction. The proposed model is discussed and its thermodynamic properties are calculated in the molecular field approximation. It is found that the magnitude of the reciprocal pitch varies nearly linearly with temperature in agreement with experiment. Interpretational difficulties related to the use of the multipole expansion are discussed.

Field‐induced deformation of hybrid‐aligned nematic liquid crystals: New multicolor liquid crystal display

Abstract: Electric field‐induced deformation is studied in a unique hybrid‐aligned nematic (HAN) cell, in which the director of a nematic liquid crystal (LC) with either positive or negative dielectric anisotropy is varied continuously, lying perpendicular to one substrate and parallel to the other. The experimental results show the absence of threshold field in the birefringence–vs–applied voltage relationship as well as the slow variation of birefringence with voltage; these phenomena are analyzed in terms of the Frank‐Oseen continuum theory. Also, the above characteristics of HAN are demonstrated to have such advantages in multicolor LC display applications as low operating voltage and fairly good color separation together with uniform and bright color generation.

The effect of quasispherical solutes on the nematic to isotropic transition in liquid crystals

Abstract: When nonmesomorphic solutes are added to nematic liquid crystals, the nematic–isotropic transition temperature is depressed and a two‐phase region is observed. The slopes, βn and βi, of the nematic and isotropic phase boundary lines in the reduced nematic–isotropic transition temperature (T*) vs solute mole fraction (x) diagrams are reported for binary mixtures of quasispherical solutes with nematic liquid crystals. The systems studied are Me4Sn, Et4C, Et4Sn, Pr4Sn, Bu4Pb, and Bu4Sn (Me = methyl, Et = ethyl, Pr = propyl, and Bu = butyl), mixed with p‐methoxybenzylidene‐p′‐n‐butylaniline (MBBA), and CCl4 mixed with p‐p′‐di‐n‐hexyloxyazoxybenzene (DHAB). Also reported are infinite dilution solute activity coefficients for several mixtures involving Et4C and CCl4. The experimental results are compared with predicted values from statistical–mechanical theories based on (a) a lattice model of hard rectangular parallelepipeds and cubes, (b) a virial expansion treatment of hard spherocylinders and spheres, and (...

Polymeric liquid crystals: Frank elasticity and light scattering

Abstract: We discuss some theoretical features of a nematic phase made of long, partially flexible chains. The bend constant K3 is dominated by the rigidity of the chains. The twist constant K2 is mainly related to the anisotropic couplings between chains. The splay constant is very large (increasing like the square of the molecular mass M). An interesting limit is obtained when the length of the extended chains is larger than the optical wavelength used in a light scattering experiment: then the scattering laws should differ qualitatively from what is known in usual nematics.

Trends in the nematic–isotropic liquid transition temperatures for the homologous series of 4-n-alkoxy- and 4-n-alkyl-4′-cyanobiphenyls

Abstract: The lower homologues of the series of 4-n-alkoxy- and 4-n-alkyl-4′-cyanobiphenyls have been prepared and their liquid crystal transition temperatures determined. The trends in the nematic–isotropic liquid (N–I) transition temperatures along the series are compared with observed trends for other homologous series. These results reveal deficiencies in the theoretical treatments that have been proposed to explain trends in N–I transition temperatures in such series. However, the results may be explained by the existence, in the case of the higher homologues, of certain alkyl chain conformations which are especially favourable to the stability of the nematic phase

AC Operated flat panel liquid crystal display

Abstract: A flat panel liquid crystal display system formed by sandwiching a thin layer of liquid crystal material between a front electrode structure, split into rows or columns, and a back electrode structure formed into desired patterns and including addressing circuitry is described. Single polarity operation of a liquid crystal display system in which the direction of current flow in the liquid crystal material is reversed at the frame rate is a feature of the invention. Operation is accomplished so as to permit gray scale rendition as response to an applied video signal. Addressing circuitry demonstrating the applicability of large scale integration (LSI) techniques is also an important element of the invention.

Computer simulation of anisotropic molecular fluids

Abstract: We have extended the molecular dynamics method to permit the simulation of systems containing cylindrically symmetric molecules with arbitrary eccentricity. This extension is accomplished by means of a potential energy function which models the primary interaction effects of molecular anisotropy, and which is mathematically convenient for computer use. The method is then applied to two problems, one involving the stability of the nematic liquid crystal phase, and the other illustrating the effect of cooperative reorientation on spectral line shapes.

Liquid crystal color display devices

Abstract: A liquid crystal color display device which comprises a first electrode; a first substrate whose surface has a property of orientating the molecules of a nematic liquid crystal parallel with said surface; a second electrode; a second substrate whose surface has a property of orientating the molecules of the nematic liquid crystal perpendicular to said surface; a nematic liquid crystal interposed between the first and second substrates; at least one polarizer; and a means whereby the birefringence of the liquid crystal cell is changed to display various colors.

Dielectric properties of 4′- n -alkyl-4-cyanobiphenyls in their nematic phases

Abstract: The principal dielectric constants of the pentyl to octyl derivatives of 4′-n-alkyl-4-cyanobiphenyl have been measured as functions of temperature in their nematic and isotropic phases. All the compounds exhibit a strong positive dielectric anisotropy due to the presence of a large dipole moment along the major molecular axis. The principal dielectric constantse ‖ ande ⊥ as well as the anisotropy Δe decrease with increasing alkyl chain length. The experimental value of $$\bar \in = \frac{1}{3}$$ (e‖+2e⊥) decreases with decreasing temperature, and is throughout less than the extrapolated isotropic value, in conformity with the model of antiferroelectric short range order proposed by Madhusudana and Chandrasekhar.