Showing papers on "Liquid crystal published in 1968"
TL;DR: In this paper, the ability of a nematic liquid crystal to cooperatively align in an electric field is used to orient "guest" dichroic dye molecules (molecules whose absorption spectrum is a function of the molecular orientation with respect to the polarization of the incident light).
Abstract: A new electro‐optic effect is presented, based on guest‐host interactions in nematic liquid crystals. The ability of a nematic liquid crystal to cooperatively align in an electric field is used to orient ``guest'' dichroic dye molecules (molecules whose absorption spectrum is a function of the molecular orientation with respect to the polarization of the incident light). Thus one can electrically switch the color of transmitted light using fields of the order of 104 V/cm.
462 citations
01 Jul 1968
TL;DR: In this article, a new electrooptic effect in certain classes of nematic liquid crystals is presented, termed "dynamic scattering" because scattering centers are produced in the transparent, anisotropic medium due to the disruptive effects of ions in transit.
Abstract: A new electrooptic effect in certain classes of nematic liquid crystals is presented. The effect has been termed "dynamic scattering" because scattering centers are produced in the transparent, anisotropic medium due to the disruptive effects of ions in transit. The ions can be produced by field assisted dissociation of neutral molecules and/or Schottky emission processes. The rise times of 1 to 5 ms and decay times of less than 30 ms, together with dc operating voltages in the 10 to 100 V range, make dynamic scattering seem attractive for such applications as alphanumeric indicators, and do not preclude its use in line-at-a-time matrix addressed, real-time displays. Reflective contrast ratios of better than 15 to 1 with efficiencies of 45 percent of the standard white have been demonstrated.
423 citations
TL;DR: In this paper, the use of nematic solvents for magnetic resonance studies on oriented molecules is described, and some of the results obtained so far are reviewed and compared with those obtained using the theory of crystalline organic liquids.
Abstract: Thermotropic mesomorphous phases such as occur in the melts of many organic substances are considered Though mesomorphous melts were first observed by Reinitzer in 1888, fundamental structural problems regarding such melts have not, as yet, been completely solved Part I of this article deals mainly with such structural problems and with the theories of crystalline organic liquids Part II describes the use of nematic solvents for magnetic resonance studies on oriented molecules Examples are given to illustrate the possibilities offered by this procedure, and some of the results obtained so far are reviewed
402 citations
TL;DR: An attempt has been made to give a complete picture of the cholesteric liquid crystal as applied to nondestructive testing, rather than to review the work actually being done in this field.
Abstract: The cholesteric phase is associated with scattering effects that give rise to iridescent colors, the dominant wavelength being influenced by very small changes in temperature, which can be as large as 1000 A shift per degree. This unusually high temperature sensitivity has given rise to the use of the cholesteric phase as a sensitive thermometer and thermal mapping media. This paper reviews the optical effects in the cholesteric phase with some new additions that are particularly relevant to thermal mapping. An attempt has been made to give a complete picture of the cholesteric liquid crystal as applied to nondestructive testing, rather than to review the work actually being done in this field.
167 citations
Patent•
23 Feb 1968
TL;DR: In this article, the authors present an image of the path of the electric field and three chromatic states, the normal color (before the electric potential is applied), the color given off when the electric fields are applied, and the color observed when the field is removed.
Abstract: This disclosure is directed to articles of manufacture, chiefly display devices, containing minute ''''naked'''' droplets or inclusions of cholesteric liquid crystal material in a substantially continuous polymeric matrix, said liquid crystal material changing color or shade of color not only upon application of an electric potential but also upon removal of the field. The image produced has a comparable outline to that of the path of the electric field. Three chromatic states are evident, the normal color (before the electric potential is applied), the color given off when the electric field is applied, and the color observed when the electric field is removed. All three chromatic states are readily discernible from one another. The polymer matrix protects the cholesteric liquid crystal droplets from aging and enhances electric field behavior because the third chromatic state (electric potential removed) has a greater longevity with the matrix-bound material versus unprotected material of identical composition but no polymeric matrix. Other advantages are also discussed.
156 citations
TL;DR: Optically negative cholesteric liquid-crystal films can be transformed to an optically positive state by applying high d-c electric fields as mentioned in this paper, where the helical structure is converted to either a planar smectic, or a linear nematic, structure.
Abstract: Optically-negative cholesteric liquid-crystal films can be transformed to an optically-positive state by applying high d-c electric fields A phase transformation occurs in which the helicoidal cholesteric structure is converted to either a planar smectic, or a linear nematic, structure The threshhold field for this transformation has been studied as a function of sample thickness, temperature and composition Bulk fields are responsible for the phenomenon It is inferred that the compositional dependences are due to size factors and internal molecular dipole moments
145 citations
TL;DR: In this paper, a new electro-optic effect based on the disruptive effects of ion transport through certain classes of nematic liquid crystals is presented, which scatters light strongly (appears white) when subjected to fields of 5 × 103 V/cm.
Abstract: A new electro‐optic effect based on the disruptive effects of ion transport through certain classes of nematic liquid crystals is presented. The initially transparent liquid scatters light strongly (appears white) when subjected to fields of 5 × 103 V/cm. Reflective contrast ratios of better than 20:1 with efficiencies of 45% of the standard white have been obtained.
136 citations
TL;DR: It was shown theoretically that nematic liquid crystals in magnetic fields may display alignment inversion walls partially similar to Bloch and Neely walls in ferromagnetics as mentioned in this paper.
Abstract: It is shown theoretically that nematic liquid crystals in magnetic fields may display alignment inversion walls partially similar to Bloch and N\'eel walls in ferromagnetics.
117 citations
TL;DR: In this article, the N.M.R. spectrum of pyridine oriented in the nematic phase of anisole-azophenyl-n-capronate has been studied.
Abstract: The N.M.R. spectrum of pyridine oriented in the nematic phase of anisole-azophenyl-n-capronate has been studied. The analysis has been carried out iteratively using a modified version of the computer programme LAOCOONII (re-named as LAOCOONOR). The details of the modification are discussed. The direct couplings are shown to be of negative sign. Ratios of the various inter-proton distances are determined irrespective of the orientation of the molecule. They agree within experimental error with the microwave results.
112 citations
01 Jan 1968
TL;DR: The mesomorphic state is surprisingly widespread in organic, and even certain inorganic, compositions as discussed by the authors, and mesomorphic material by the ton occurs as an intermediate in processing, and the layered "smectic" structure of the industrially important "neat" phase will serve as an introduction to mesomorphic structures.
Abstract: Synopsis-"Liquid crystals" are "mesomorphic" structure types between liquids, which are random, and crystals, which are periodic in all three dimensions. The mesomorphic state is surprisingly widespread in organic, and even certain inorganic, compositions. In the surfactant industry, mesomorphic material by the ton occurs as an intermediate in processing. The layered "smectic" structure of the industrially important "neat" phase will serve as an introduction to mesomorphic structures. In each layer, elongate•t molecules or other units are arranged parallel to each other and with their head ends at the interface between layers; the stacking of layers is periodic. Laterally, however, the molecules have a random, liquidlike arrangement. Thus a single structure has a hybrid liquid and crystalline nature. The layers, however, slide easily over each other and the structure flows under its own weight even while maintaining crystallike periodicity. The chemical and physical factors leading to this and other mesomorphic structures in surfactant compositions are reviewed.
80 citations
TL;DR: Of particular interest in living systems are liquid crystals, which are formed by cholesteric esters and many protein materials, and the two-dimensional crystals (smectic structure), which are form by fatty acid derivatives.
Abstract: Most lipids do not pass, on heating, directly from a crystalline structure to an isotropic structure. They are often characterized by a number of intermediate phases, ranging from the plastic crystal, where the center of gravity of the molecule may rotate about one or more axes while the three-dimensional order of the crystal remains, to nematic liquid crystals, which have birefrigent properties of crystals and yet are characterized by completely random ordering of the molecular centers. The smectic and cholesteric liquid crystalline structures are most commonly encountered in lipids. The structural characteristics of these systems are discussed. Of particular interest in living systems are liquid crystals, which are formed by cholesteric esters and many protein materials, and the two-dimensional crystals (smectic structure), which are formed by fatty acid derivatives. The mechanisms of energy transfer and the mechanical alignment in these liquid crystalline systems are unique and require different considerations from those found adaptable to liquids or solids. The properties of liquid crystals which might best be associated with living systems will be discussed, including surface properties and diffusivity.
Patent•
11 Jun 1968
TL;DR: In this article, a system incorporating liquid crystals which are thermally sensitive and optically responsive to temperature changes is described, and the authors propose a method to incorporate liquid crystals into the system.
Abstract: Systems incorporating liquid crystals which are thermally sensitive and optically responsive to temperature changes.
TL;DR: In this article, a theory of the very high rotatory power exhibited by cholesteric liquid crystals is developed by the use of the Jones calculus for optical systems, based on the model proposed by de Vries in which the liquid crystal is regarded as a large number of thin birefringent layers arranged helically.
Abstract: A theory of the very high rotatory power exhibited by cholesteric liquid crystals is developed by the use of the Jones calculus for optical systems. The calculations are based on the model proposed by de Vries in which the liquid crystal is regarded as built up of a large number of thin birefringent layers arranged helically. When light is incident normal to the layers, i.e. along the screw axis, selective reflexion of one of the circularly polarized components takes place and the rotatory dispersion in the neighbourhood of the region of reflexion is anomalous. The reflexion curve and the amplitude attenuation factor, exp (−ξ), for circularly polarized light at normal incidence are derived as functions of wavelength by setting up difference equations closely similar to those formulated by Darwin in his dynamical theory of X-ray diffraction. Within the range of total reflexion, ξ is real, primary extinction occurs and the medium is highly circularly dichroic. The spectral width of the reflexion and the primary extinction coefficient predicted by theory compare favourably with the experimental values. Outside the region of total reflexion, ξ is imaginary and opposite in sign on opposite sides of the reflected band. This is responsible for the reversal of the sign of the rotation on crossing the band. The anomalous part of the rotation is a direct measure of the phase of the primary wave given by the dynamical theory.
TL;DR: In this article, a new reflective optical storage effect has been found in mixtures of certain nematic liquid crystals and cholesteric liquid crystals when subjected to a dc field, the initially clear material becomes milky white and remains in this state when the field is removed.
Abstract: A new reflective optical storage effect has been found in mixtures of certain nematic liquid crystals and cholesteric liquid crystals. When subjected to a dc field, the initially clear material becomes milky white and remains in this state when the field is removed. The material can be rapidly switched back to its clear state by an audio‐frequency signal. A preliminary model based on the principle of a field‐induced emulsion gives rough agreement with experiment.
Patent•
23 Feb 1968
TL;DR: In this paper, an image of a cholesteric liquid crystal with three chromatic states, the normal color before the electric potential, the color given off when the electric field is applied, and the color observed when the field is removed, is presented.
Abstract: This disclosure is directed to articles of manufacture, chiefly display devices, containing encapsulated cholesteric liquid crystals which change color or shade of color not only upon application of an electric potential but also upon removal of the field. The image produced has a comparable outline to that of the path of the electric field. Three chromatic states are evident, the normal color (before the electric potential is applied), the color given off when the electric field is applied, and the color observed when the electric field is removed. All three chromatic states are readily discernible from one another. The encapsulation of the cholesteric liquid crystal provides an unusual advantage regarding electric field behavior because the third chromatic state (electric potential removed) has a much greater longevity with the encapsulated material versus unencapsulated material of identical composition. Other advantages are also discussed.
Patent•
03 Sep 1968TL;DR: In this paper, the light modulator is comprised of a nematic liquid crystal composition of p-acyloxybenzylidene anils and means for applying an electric field across the composition.
Abstract: The light modulator is comprised of a nematic liquid crystal composition of p-acyloxybenzylidene anils and means for applying an electric field across the composition.
TL;DR: A cholesteric-nematic phase transition can be induced by relatively weak electric fields, and the threshold field varies inversely with the pitch of the helix in corroboration of recent theoretical suggestions.
Abstract: A cholesteric-nematic phase transition can be induced by relatively weak electric fields, and the threshold field varies inversely with the pitch of the helix in corroboration of recent theoretical suggestions. The phase change is accompanied by a change in the activation energy for charge-carrier production and can easily be observed by both conductivity measurements and direct optical examination.
30 Dec 1968
TL;DR: In this paper, electric field strength and helix pitch in induced cholesteric-nematic phase transitions were analyzed for charge carrier production and the activation energy for carrier production.
Abstract: Electric field strength and helix pitch in induced cholesteric-nematic phase transitions, noting activation energy for charge carrier production
TL;DR: In this article, the effect of spinning the sample tube in the nematic range is examined, and the indirect long-range HH and FF couplings are + 2·7 and +2·2 hz.
Abstract: The high-resolution N.M.R. spectra of dimethyl-acetylene and perfluorodimethyl-acetylene have been observed in nematic phases. The effect of spinning the sample tube in the nematic range is examined. The indirect long-range HH and FF couplings are +2·7 and +2·2 hz. Structural information obtained, on the assumptions that the effects of nuclear vibrations and anisotropy in the indirect couplings are negligible, is compared with microwave and electron diffraction data, and the FCF angle is found to be 110.5° + 0.5° in contrast to earlier estimates of 107·5°. The anisotropy of the chemical shift for a CF bond in perfluorodimethyl-acetylene is about + 145 p.p.m.
01 Dec 1968
TL;DR: In this paper, a reflective television display, operating off-the-air, is described, which uses the dynamic scattering mode (DSM) in nematic liquid crystals and can be viewed in high-brightness ambients.
Abstract: A new reflective television display, operating off the air, is described. The display uses the dynamic scattering mode (DSM) in nematic liquid crystals and can be viewed in high-brightness ambients. The liquid crystal cell, 6 to 12 µm thick, was addressed in real time by means of an electron beam using a wire-mosaic faceplate on a demountable cathode ray tube. Two different liquid crystal materials--anasylidene paraamino phenyl acetate (APAPA) and an RCA proprietary room temperature liquid crystal--were tested with similar results except for the difference in operating temperature (82 to 110° C and room temperature, respectively). The resolution of the 3.1-cm-square display was somewhat less than that required for commercial television (∼150 lines), limited by the mosaic structure but not the liquid crystal. Adequate resolution should be achievable in slightly larger displays. The contrast was not optimized (7.5 to 1) but several techniques are available to improve this value to 15 or 20 to 1 as has been demonstrated in static displays. The subjective evaluation of this display points out the attractiveness of reflective television panels; under suitable external illumination the panel has a wide viewing angle (±45° approximately). The current and voltage requirements to achieve the DSM in liquid crystals are such as to raise hopes that an integrated addressing approach suitable for flat television panels can be found.
01 Jul 1968
TL;DR: In this paper, a liquid crystal technique was used for mapping temperature distributions on model aircraft surfaces in boundary layer flow tests, and the results showed that the method can be applied to a wide variety of aircraft surfaces.
Abstract: Liquid crystal technique for mapping temperature distributions on model aircraft surfaces in boundary layer flow tests
Patent•
16 Oct 1968TL;DR: The speed of response of a liquid crystal is increased without degrading the crystal, by applying the crystal an electric field which is of substantially greater value than the minimum value of field required to achieve substantially maximum light scattering from the crystal and, after a short interval, reducing the magnitude of the applied field to a value close to said minimum value.
Abstract: The speed of response of a liquid crystal is increased without degrading the crystal, by applying the crystal an electric field which is of substantially greater value than the minimum value of field required to achieve substantially maximum light scattering from the crystal and, after a short interval, reducing the magnitude of the applied field to a value close to said minimum value.
TL;DR: In this paper, the experimental results for the photographic scattering of mesophases of cholesteryl myristate are presented, and the patterns for the cholesteric state are similar to those for spherulitic polymers and are analyzed using the theory for scattering from media exhibiting nonrandom orientation correlations.
TL;DR: In this paper, a high-resolution N.M.R. study of 3,3,3-trifluoropropyne in different liquid crystals is reported.
Abstract: A high-resolution N.M.R. study of 3,3,3-trifluoropropyne in different liquid crystals is reported. The relative geometry obtained agrees with microwave data. The sign of J (HF) is negative. The anisotropies in fluorine and proton chemical shifts have been measured, and are comparable in magnitude and sign with values previously reported for similar compounds.