Showing papers in "Molecular Crystals and Liquid Crystals in 1987"
TL;DR: In this article, the authors describe a new class of light control films consisting of submicron liquid crystal droplets dispersed in ultraviolct-cured polymer matrices, which can respond optically to both applied electric fields and temperature changes.
Abstract: This paper describes a new class of light control films consisting of submicron liquid crystal droplets dispersed in ultraviolct-cured polymer matrices. These films, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters. The optical performance of these films depends on a variety of structural, electro-optical and thermal properties. This report describes scanning electron microscope studies of film structure, measurements of voltage dependent film transmittance and light scattering, and calorimetric studies which indicate that microdroplet formation in the films occurs as a result of phase separation which takes place during the cure process.
213 citations
TL;DR: A series of thermotropic poly(1,4-phenylene-2,5-di-nalkoxy terephthalate)s with the length of the n-alkoxy side chains being varied between n = 2 and n = 18 carbon atoms has been examined by optic as mentioned in this paper.
Abstract: A series of thermotropic poly(1,4-phenylene-2,5-di-n-alkoxy terephthalate)s with the length of the n-alkoxy side chains being varied between n = 2 and n = 18 carbon atoms has been examined by optic...
114 citations
TL;DR: In this article, the authors describe light control films consisting of submicron liquid crystal droplets dispersed in epoxy matrices, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters.
Abstract: This paper describes light control films consisting of submicron liquid crystal droplets dispersed in epoxy matrices. These films, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters. The optical performance of these films depends on a variety of structural, electrooptical and thermal properties. This paper describes scanning electron microscope studies of film structure, measurements of voltage dependent film transmittance, contrast ratio and light scattering, and calorimetric studies of the cure process which governs microdroplet formation in the films.
110 citations
TL;DR: In this paper, structural and material properties of ferroelectric liquid crystals are reviewed with emphasis on their relevance for electro-optic effects and device applications, focusing on properties of prime importance for device dynamics.
Abstract: Recent developments in understanding structural and material properties of ferroelectric liquid crystals are reviewed with emphasis on their relevance for electro-optic effects and device applications. In only a few years the material situation has changed from one characterized by an almost complete lack of technically useful materials to one, not yet adapted to technical needs, but beginning to offer interesting, commercially available ferroelectric mixtures. The present device limitations can, however, be tracked down, not so much to the principal non-availability of materials as to the lack of understanding of which material properties are desirable and needed, in particular to permit simple and efficient matrix addressing. Thus we have centered our discussion to properties of prime importance for device dynamics in this review, which also contains a general discussion of material properties based on the molecular structure, as well as an assessment of the present industrial development.
75 citations
TL;DR: In this article, the experimental findings about bowlic mesophases are briefly summarized, including phase transitions and other physical properties (optical, elastic, flexoelectric and hydrodynamic, as well as defects) and possible instabilities and applications are discussed.
Abstract: A new type of liquid crystals made up of bowl-like molecules was predicted by Lin in 1982 and was recently synthesized. In is paper, the experimental findings about these bowlic mesophases are briefly summarized. Possible mesophases (polar nematic, non-polar nematic, cholesteric, stringbean, donut, columnar, etc.) are proposed and discussed. The possible breakdown of the macroscopic symmetry n → – n (n is the director) in these mesophases is emphasized. Novel properties including phase transitions and other physical aspects (optical, elastic, flexoelectric and hydrodynamic, as well as defects) are presented. Molecular engineering to produce new compounds (e.g. anisotropic ferromagnetic fluid and bowlic polymers) is suggested. Possible instabilities and applications are discussed. The possibility of second harmonic generation and simple sub-microsecond electro-optical switching (without the complications encountered in ferroelectric smectic C*) in these bowlic mesophases are pointed out. These bow...
65 citations
TL;DR: The correlation between the molecular structure and the magnitude and sign of the spontaneous polarisation of ferroelectric liquid crystals has been studied using mixtures and pure compounds as discussed by the authors, and several binary mixtures consisting of a chiral dopant and a non chiral smectic C compound have been prepared.
Abstract: The correlation between the molecular structure and the magnitude and sign of the spontaneous polarisation of ferroelectric liquid crystals has been studied using mixtures and pure compounds. Several binary mixtures consisting of a chiral dopant and a non chiral smectic C compound have been prepared. The spontaneous polarisation with values up to 10 nC/cm2 for mixtures containing 10% of a chiral dopant was measured. Three homologous series of new ferroelectric liquid crystals which show values of the spontaneous polarisation up to 300 nC/cm2 have been prepared by the esterification of 4-alkyloxy-4′-hydroxybiphenyls with three a-chloro carboxylic acids obtained from the a-amino acids valine, leucine, and isoleucine. Within a homologous series the spontaneous polarisation was found to increase considerably with decreasing alkyl chain length to an extend which could not be explained by the behaviour of the tilt angle which increases only slightly.
59 citations
TL;DR: The stress transients resulting from step-wise changes in shear rate have been investigated for a liquid crystalline solution of PBLG in m-cresol in this paper.
Abstract: The stress transients resulting from step-wise changes in shear rate have been investigated for a liquid crystalline solution of PBLG in m-cresol In step-up experiments these transients display a complex profile which includes multiple maxima, even in the Newtonian region To a first approximation the curves scale with strain A stepwise decrease in shear rate also causes a stress pattern with multiple maxima The initial decay is related to the stress relaxation upon cessation of flow Many of these features are not described by the existing theories They are explained in terms of supermolecular structures such as domains
58 citations
TL;DR: In this paper, the first x-ray scattering measurements from freely suspended lipid (DMPC)-water multilayer films were performed in a controlled temperature and humidity (0% to 100%) environment.
Abstract: We report the first x-ray scattering measurements from freely suspended lipid (DMPC)-water multilayer films. By combining several techniques, we are able to grow stable, oriented films of various thicknesses (∼102 to 104 A) in a controlled temperature (0°C to 80°C) and humidity (0% to 100%) environment. A specially designed film holder allows both transmission and reflection x-ray measurements. Very importantly, the humidity control system allows us to construct the temperature-chemical potential phase diagram in addition to the normally studied temperature-concentration phase diagram. Our most important results are as follows. First, we find a metastable Lα phase in bulk DMPC-water mixtures when the water concentration is between 30 and 40 weight percent, and second, from the variation of the interplanar peak position as a function of concentration and chemical potential, we are able to deduce the functional form of the interaction force between layers in the Lα. phase. This form is found to be ...
58 citations
TL;DR: In this article, two new octa-substituted disk-like bis(β-diketonato) copper(II) complexes, 8C 8-Cu and 8C8O-Cu, have been synthesized and the thermal behavior of these three complexes was investigated by means of microscopic observations and DSC measurements.
Abstract: Two new octa-substituted disk-like bis(β-diketonato) copper(II) complexes, 8C8-Cu and 8C8O-Cu, have been synthesized. The same type of octa-substituted copper complexes, SC9O-Cu, which was synthesized for the first time by A. M. Giroud-Godquin et al., has also been prepared. The thermal behavior of these three complexes was investigated by means of microscopic observations and DSC measurements. It was found that the 8C8-Cu exhibits not a discotic mesomorphism but a usual double melting behavior via the isotropic liquid, and that the 8C8O-Cu exhibits an unusual double melting behavior via the discophase which had not been reported by A. M. Giroud-Godquin et al. Furthermore, it was found that the 8C8O-Cu exhibits a new thermal phenomenon of “double clearing behavior” which is originated from a superheating of the transition from the crystalline phase to the discotic phase. Such double clearing behavior of the 8C8O-Cu is the first example in the mesomorphic compounds, so far as we know.
55 citations
TL;DR: In this paper, new nematic liquid crystalline phenylcyclohexanes with a terminal side-chain vinylic group some distance from the rigid core and both polar and non-polar terminal side chain groups, were synthesized.
Abstract: New nematic liquid crystalline phenylcyclohexanes with (i) a terminal side-chain vinylic group some distance from the rigid core and (ii) both polar and non-polar terminal side-chain groups, were synthesized. Investigations of their elastic, birefringence, dielectric and rotational viscous properties have shown several new odd-even effects. These are attributed to side-chain Simultaneous odd-even effects were found for δϵ, δn, k 33/k11 and K = k 11 + (k 33 - 2k 22)/4. Furthermore, unusually low twist elastic constants, k 22 were obtained for polar 6-alkenyls as well as for compounds exhibiting groups with permanent dipole moments in even side-chain positions.
54 citations
TL;DR: In this article, the orientation behavior of crosslinked liquid crystal line side chain polymers is determined by IR-dichroism measurements and the order parameter S has the same temperature dependence and is of the same magnitude as in the corresponding uncrosslinked liquid crystalline polymers.
Abstract: The orientation behavior of crosslinked liquid crystal-line side chain polymers is determined by IR-dichroism measurements. In stretched samples the conformation of the polymer main chain and the chemical constitution of the rodlike side chain determine the position of the director in relation to the axis of stress. The order parameter S has the same temperature dependence and is of the same magnitude as in the corresponding uncrosslinked liquid crystalline polymers. The order parameter and the nematic to isotropic phase transformation temperature are independent of the applied mechanical stress under the experimental conditions (elongation up to 50%).
TL;DR: A new family of ferroelectric liquid crystals is presented in this article, and some mixtures of compounds from this family show an interesting combination of high spontaneous polarization, good alignme...
Abstract: A new family of ferroelectric liquid crystals is presented. In particular, some mixtures of compounds from this family show an interesting combination of high spontaneous polarization, good alignme...
TL;DR: In this article, the morphology of blends of Liquid Crystalline (LC) co-polyesters and polyethylene terephthalate (PET) with a varying percentage of the liquid crystalline component were studied primarily by small angle light scattering (SALS), polarising microscopy and wide angle X-ray diffraction.
Abstract: Morphology of blends of Liquid Crystalline (LC) co-polyesters and polyethylene terephthalate (PET) with a varying percentage of the liquid crystalline component were studied primarily by small angle light scattering (SALS), polarising microscopy and wide angle X-ray diffraction. The crystallization behaviour of these blends was studied with the help of density measurements and differential scanning calorimetry (DSC). It was observed that a small amount of LC component in PET changes the morphological and crystallization behaviour of PET. It also affects the mechanical properties of PET significantly.
TL;DR: In this article, a series of ferroelectric liquid crystals with neighbouring chiral carbons or a chiral carbon with C-CI binding next to the molecular dipole moment (C=O) are synthesized utilizing isoleucine, valine, leucine and 2-amino butanoic acid as starting materials and are found to possess extremely large spontaneous polarization exceeding 3 × 10−7C/cm2 and dielectric constants larger than 7000.
Abstract: New series of ferroelectric liquid crystals with neighbouring chiral carbons or a chiral carbon with C—CI binding next to the molecular dipole moment (C=O) are synthesized utilizing isoleucine, valine, leucine, amylalchol and 2-amino butanoic acid as starting materials and are found to possess extremely large spontaneous polarization exceeding 3 × 10−7C/cm2 and dielectric constants larger than 7000. These compounds are found to exhibit a novel dielectric behaviour such as hysteresis in the temperature dependence due to the strong molecular interaction with surfaces. The response of electro-optic elements prepared with these ferroelectric liquid crystals is found to be very fast, in the μsec range, even at room temperature.
TL;DR: The molecular structural characteristics which give rise to large optical nonlinearities have been delineated by several key steps and has led to the development of a structural algorithm for the design of β molecules with high susceptibilities as discussed by the authors.
Abstract: The molecular structural characteristics which give rise to large optical nonlinearities have been delineated. This has been accomplished by several key steps and has led to the development of a structural algorithm for the design of β molecules with high susceptibilities. High activity molecular units have been covalently attached to form polymers which can contain up to 100% of the NLO moiety, and the resulting molecular optical properties have been characterized. The second order molecular susceptibility was found to be undiminished by properly designed covalent bonding to form a polymer, and spectral characteristics were found to closely follow that of the NLO unit.
TL;DR: In this paper, the spatial distribution of collagen can correspond to the geometry adopted by molecules in cholesteric liquid crystals; in compact bone the twist appears between fibrils, forming helices, and disposed along coaxial cylinders.
Abstract: In biological structures the spatial distribution of collagen can correspond to the geometry adopted by molecules in cholesteric liquid crystals; in compact bone the twist appears between fibrils, forming helices, and disposed along coaxial cylinders. In thin sections of self assembled collagen gels twisted structures have been observed; the geometry of the fibril aggregates corresponds to a cylindrical twist. In dehydrated drops of collagen solutions the textures observed are related to cholesteric and hexagonal pseudomorphoses. The liquid crystalline behaviour of collagen in these different situations is discussed.
TL;DR: In this paper, the influence of an electric field on the SmC*-SmA transition of two new ferroelectric liquid crystals is investigated, and the transition temperature is found to vary linearly with applied field strength, which is calculated by simple thermodynamic arguments.
Abstract: The influence of an electric field on the SmC*-SmA transition of two new ferroelectric liquid crystals is investigated. At temperatures just above the SmC*-SmA transition double hysteresis loops are observed similar to that known for solid Cerroelectrics indicating a field induced first order transition to the ferroelectric phase. The first order character of the SmC* -SmA transition of the two compounds under investigation is supported by DSC and tilt angle measurements. With field strength of about 50 kV/ cm the transition temperature is enhanced by 1 K. The shift of the SmC*-SmA transition temperature, which is found to vary linearly with applied field strength, can be calculated by simple thermodynamic arguments.
TL;DR: In this article, the effect of the chiral molecules appears in the effective elastic constant, ke, which will decrease and then increase with respect to the increasing of the concentration of the Chiral molecules.
Abstract: The ferronemtaic state which was described theoretically by Brochard and de Gennes can be achieved by doping the liquid crystal with anisotropic ferromagnetic particles. The homeotropic liquid crystal film was successfully prepared for the ferronematic liquid crystal doped with low concentration chiral molecules. The magnetic-field-induced-birefringence due to molecular reorientation was treated both theoretically and experimentally. In the low field regime (<2.5G), it is theoretically predicted that the induced phase difference between the ordinary and extraordinary ray of a normally incident probe beam is proportional to the square of the external magnetic field and to the fifth power of the thickness of the sample film. This is verified by the experimental results. The effect of the chiral molecules appears in the effective elastic constant, ke , which will decrease and then increase with respect to the increasing of the concentration of the chiral molecules.
TL;DR: In this paper, a parallel plate apparatus was used to observe the formation of the banded texture in HPC solutions after shear and a curve on the shear rate-total deformation plane was determined, giving the threshold for band formation.
Abstract: A parallel plate apparatus was used to observe the formation of the banded texture in HPC solutions after shear. A curve on the shear rate-total deformation plane is determined, giving the threshold for band formation. The position of such a curve is found to depend strongly on sample thickness.
TL;DR: In this article, the rheological properties of a 20% solution of poly-para-phenylene-therephthalamide (PpPTA) in concentrated sulfuric acid have been investigated using a Contraves Rheomat 135S and a device that allows microscopic investigation of the solution during transient shear flow using polarized light.
Abstract: The rheological properties of a 20% (w/w) solution of poly-para-phenylene-therephthalamide (PpPTA) in concentrated sulfuric acid have been investigated using a Contraves Rheomat 135S and a device that allows microscopic investigation of the solution during transient shear flow using polarized light.
TL;DR: In this article, the authors present new data and estimates for the effects of lipid charge and lipid layer thickness on lipid swelling and liposome formation in liquid crystalline state, and the basic conclusion is that the electric fields can affect lipid swelling by at least six mechanisms: electrostatic interactions between the field and the bilayers, electroostnotically induced mechanical stresses, redistribution of double layer counter-ions between the bilayer, decreased surface, membrane arid line, etc.
Abstract: External electric fields can induce liposorne formation on electrode surfaces if the swelling lipid is in liquid crystalline state. The lipid swelling and liposome formation depend on the type of the lipid, the dried lipid layer thickness, the medium parameters (temperature, osmolarity, ionic strength), the type and the parameters of the electric field (direct current (DC) or alternating current (AC), amplitude, frequency) and the time of exposure. This paper reviews some of our previous experimental results and theoretical estimates for those effects and presents new data and estimates for the effects of lipid charge and lipid layer thickness. The basic conclusion is that the electric fields can affect lipid swelling and liposome formation by at least six mechanisms: (1) electrostatic interactions between the field and the bilayers, (2) electroostnotically induced mechanical stresses, (3) redistribution of double layer counter-ions between the bilayers, (4) decreased surface, membrane arid line ...
TL;DR: In this paper, two possible ways of the one-dimensional variation of the K13 nematic surface-like volume energy are discussed and the three-dimensional solution for a variational problem including a nematic energy density containing both first and second spatial gradients has been found on the basis of Ericksen & Toupin variational arguments.
Abstract: Two possible ways of the one-dimensional variation of the K13 nematic surface-like volume energy are discussed. The first way of variation when the deformation angle θ and its derivative θ’ are considered as independent functions at the boundary shows that the K13 problem has no solution. The second way of variation when θ and θ’ are considered as dependent functions at the boundary shows that the problem can be solved by introducing of the inverse function and variation of a functional with a movable boundary. The three-dimensional solution for a variational problem including a nematic energy density containing both first and second spatial gradients has been found on the basis of Ericksen & Toupin variational arguments. The surface and body forces as well as the generalized surface and body forces were obtained. The surface molecular field including the K13 term was obtained in explicit form. This field for the one-dimensional case unambiguously confirms the validity of our boundary conditions ...
TL;DR: In this paper, six dimeric compounds with two rigid cores connected by a central spacer group are described and the ΔH and ΔS parameters for the nematic-isotropic (clearing) transition are investigated.
Abstract: Six Twin dimeric compounds having two rigid cores connected by a central spacer group are described. Two types of rigid units, 4-pentyloxyphenyl cinnamates and 4-cyano-4-oxybiphenyl, were employed. The spacer groups were pentamethylene (PM), diethylene oxide (EO) and disiloxane (DS). For each rigid core the nematic-isotropic temperature followed the order PM > EO > DS. Investigation of the ΔH and ΔS parameters for the nematic-isotropic (clearing) transition revealed that for these compounds the clearing transition was driven by ΔS. The EO mesogens have larger ΔS values than for the PM mesogens, which result in lowered clearing temperatures due to relatively constant ΔH values. The conformational preference for gauche isomers in the spacer of the EO compounds is seen as conducive to proper orientational alignment of the rigid cores in the nematic phase, better so than for the PM and DS spacers.
TL;DR: In this article, spontaneous polarization was measured for two chemically isomeric ferroelectric smectogens that have different phase sequences, S-4-n-decyloxyphenyl 4-(3,‘7’-dimethyloctyloxy) phenyl 4-ndecyloxybenzoate and S- 4-m-dimethylamine benzoate, which differ only in the direction of the central ester linkage.
Abstract: The spontaneous polarization was measured for two chemically isomeric ferroelectric smectogens that have different phase sequences. The two compounds, S-4-(3,‘7’-dimethyloctyloxy) phenyl 4-n-decyloxybenzoate and S-4-n-decyloxyphenyl 4-(3,‘7’-dimethyloctyloxy) benzoate differ only in the direction of the central ester linkage. Thus, both materials have similar dipolar characters. The first material exhibits a smectic A to smectic C* phase transition, whereas the second exhibits a cholesteric to smectic C* phase change. The optical tilt angle for the first compound saturates, close to 22 degrees in the smectic C* phase, whereas the second has a relatively large temperature independent value of approximately 45 degrees. Concomitantly, the magnitude of the spontaneous polarization of the first material is less than that of the second. The temperature dependence of the polarization of these materials was also measured. It is concluded for materials that are isomeric that the relative size of the polar...
TL;DR: In this article, the authors presented an expression for the reorientation of the nematic director under the influence of an applied voltage of any magnitude, which was extended to study the capacitance of a nematic layer under any magnitude of applied voltage.
Abstract: For the first time, expressions are presented which enable us to calculate the reorientation of the nematic director under the influence of an applied voltage of any magnitude. The mathematical techniques developed are extended to study the capacitance of a nematic layer under any magnitude of applied voltage. The calculation of the capacitance of the nematic layer up to high applied voltages allows the identification of a new high voltage linear relationship between capacitance and applied voltage. This new linear relationship has potential for enabling the anisotropic dielectric permittivity of liquid crystal materials to be measured experimentally with more accuracy and ease than before.
TL;DR: In this article, a survey on the synthesis and mesomorphic properties of organometallic or coordination transition metal complexes is presented, dealing with palladium (II) complexed with three different classes of azobenzene ligands.
Abstract: A survey on the syntheses and mesomorphic properties of some organometallic or coordination transition metal complexes is reported. In particular, this review is dealing with palladium (II) complexed with three different classes of azobenzene ligands namely p-alkoxy(or p-alkyl) p'-ester azobenzenes, p-alkoxy-p'-alkylazobenzenes and p-alkoxy-phenil azo benzenes. A preliminar account on the synthesis, characterization and structural properties of a series of smectic copper (II). Schiff bases coordination compounds, together with a simple molecular model, is also presented.
TL;DR: In this article, the deuterium NMR is used to indicate the degree of ordering of the PBLG helix axis in lyotropic phases and the preparation of magnetically oriented gels in benzyl alcohol is described.
Abstract: Deuterium NMR is used to indicate the degree of ordering of the PBLG helix axis in lyotropic phases. Sources of difficulty when comparisons are made with theory are emphasized. The preparation of magnetically oriented gels of PBLG in benzyl alcohol is described. Delineation of the phase boundaries with NMR probes is a convenient way to monitor the gelation process. The synthesis and properties of PBLG having the benzyl ester exchanged for oligomers of ethylene glycol is presented.
TL;DR: In this paper, two series of liquid crystals are synthesized, viz. 4′-(2-ethoxy) propoxy)alkoxyphenyl 4-alkoxybenzoate, 2, (abbreviated Cm-Cn-OEt*) and 4′(2-chloro)propoxy,alkoxymboloxy,4-alkoxymhenyl, 4-alkymboloxybenzosate, 3,
Abstract: We have synthesized two series of liquid crystals, viz. 4′-(ω-(2-ethoxy) propoxy)alkoxyphenyl 4-alkoxybenzoate, 2, (abbreviated Cm-Cn-OEt*) and 4′-(ω-(2-chloro)propoxy)alkoxyphenyl 4-alkoxybenzoate, 3, (abbreviated Cm-Cn-Cl*). Compounds belonging to the latter mainly exhibit smectic A and B phases while the former show enantiotropic smectic C* at or near room temperature as well as A and smectic phases of higher order. The magnitude of the spontaneous polarization is moderate (–4 nC/cm2). There is no alteration in sign for the spontaneous polarization and for the helical pitch as function of the n value. The Cm-C3-OEt* and Cm-C5-OEt* compounds are exhibiting unusually long helical periodicity for a pure compound (30–50 μm). Compounds of series 2 also show a close relationship between spontaneous polarization and tilt angle giving a practically temperature independent ratio P/θ, making the definition of a material constant Po = P/θ meaningful.
TL;DR: In this article, the form of ferroelectric smectic C* electrooptical response vs the layer thickness and the angle β between the polarizer and analyser is investigated.
Abstract: The form of ferroelectric smectic C* electrooptical response vs the layer thickness and the angle β between the polarizer and analyser is investigated. The criterion of the smectic C*-switching rate is propozed and the method for the rotational viscosity measurements is developed.
TL;DR: In this paper, out-of-plane complexes (Pb11 and Sn11) of octasubstituted phthalocyanine derivatives have been prepared and characterized by a large dipole moment perpendicular to the macrocycle plane.
Abstract: Out-of-plane complexes (Pb11 and Sn11) of octasubstituted phthalocyanine derivatives have been prepared. They are characterized by a large dipole moment perpendicular to the macrocycle plane. The lead derivatives are shown to form columnar liquid crystals as characterized by optical microscopy, differential scanning calorimetry and X-ray diffraction at small angle.