New Cholesteric and Nematic Lyotropic Mesophases from Di-Sodium N-Lauroyl-Aspartate

Lyotropic liquid crystals are prepared from racemic and optically active di-sodium N-lauroyl aspartate (SNLA). The optically active levo enantiomer is a suitable amphiphile for obtaining cholesteric lyotropic mesophases. In the present work, different types of mesophases, including cholesteric and nematic, were prepared and their type I or II magnetic behavior characterized by deuterium and ²³Na NMR. The polarizing microscope textures were investigated, particularly with regards to magnetic field effects upon the samples. The usual chevron pattern was obtained for particular sample orientations and several characteristic effects were observed for the type I cholesteric lyomesophase in the first few minutes following removal of the sample from the magnetic field. Although the head group of di-sodium N-lauroyl aspartate possesses two negative charges, compositions are not too different from those reported for other amphiphile lyotropic systems.     

The Thermal Properties of 1,3,5-Trisubstituted Benzenes

Summary-1,3,5-Tricholesteryloxycarbonyloxy(I), 1,3,5-tri-β-sitosteryloxycarbonyl(II). and 1,3,5-tricholesteryloxycarbonylbenzene(III) form mesophases, presumably the discotic cholesteric phase.     

Studies of Specific Adsorption Sites for Sodium Ion and Water on the Interface of Mixed Micelles of Novel Type II Lyomesophases

Novel aqueous type II lyotropic mesophases that align in magnetic fields have been synthesized for binary and ternary mixtures of amphiphiles. A system in which major components of the micelle bilayer are decyltrimethylammonium and dodecanoate ions is an aligning mesophase from 100% to 35% dodecanoate, but replacement of the cationic amphiphile with hexadecyltrimethylammonium facilitates the extension to aligning mesophases up to 100% replacement of the dodecanoate ions. A study of sodium and deuterium quadrupole splittings observed in their nuclear magnetic resonance spectra, confirms and extends a three site adsorption theory for sodium ion in the mixed head group interface. The first site is associated with more strongly hydrated ions and head groups and involves adjacent dodecanoate head groups, the second is not so strongly hydrated and involves one dodecanoate group while the third is a weakly bound water at - N(CH₃)⁺ groups and a sodium remote from the interface layer in close to average isotropic motion.

Mixed detergent mesophases of type II, which spontaneously align in the field, have also been synthesized from variable mixtures of hexadecyltrimethylammonium bromide and decylammonium chloride and from mixtures of potassium dodecanoate and sodium decylsulphate. In the mixed cationic system the sodium quadrupole splittings are always low but water is tightly bound to the -NH₃ ⁺ head group. In the anionic detergent mixture sodium appears about as strongly bound to dodecanoate and decylsulphate head groups. In most of the mixed mesophases some decanol is required (maximum 25% of the bilayer) in order to render the desired type II mesophase stable over a range of mixtures of the charged detergents. Specific site adsorption for sodium and water, peculiar to different head groups renders the effect of the added decanol as primarily a convenient diluent in the bilayer to preserve mesophase integrity.     

Proton Spin Relaxation in the Rod Micelles of Type I CM Mesophases

The dynamics of the hydrocarbon chains in lyotropic nematic type I cylindrical micellar liquid crystals prepared with D₂O has been selectively studied by Zeeman and rotating frame nuclear spin-lattice relaxation. The measurements of the proton spin-lattice relaxation time T ₁ as a function of frequency and temperature demonstrate that relatively fast local fluctuations of individual amphiphilic chains relax the proton spins at high magnetic fields. This process is facilitated also by the rapid diffusive motion of the chains within the micellar units. The rotating frame Zeeman relaxation time T _1x, is associated at room temperature with a long correlation time of ~11 μs. Slow micellar orientational fluctuations have been assigned to this characteristic time.     

Topology of a Surface of the Phase Diagram of the Cholesteric Lyotropic Mesophase: Potassium Laurate/1-Decanol/Water/I-N-Lauroyl Potassium Alaninate

A surface of the phase diagram of the lyotropic cholesteric mesophase of potassium laurate/1-decanol/H₂O/l-N-lauroyl potassium alaninate (l-LAK) is studied by optical microscopy and X-ray diffraction as a function of the relative molar concentration of l-LAK and temperature. Cholesteric discotic and calamitic phases are observed and also a large domain of biaxial cholesteric phase. The inverse pitch as a function of the l-LAK relative molar concentration presents a linear behavior in the doping range studied. The l-LAK doping and its influence in favoring cholesteric calamitic phase formation are discussed in terms of the packing of the l-LAK amphiphile in the bilayer and the orientational fluctuations of the intrinsically biaxial correlation volumes.     

Nano Molecular Self Assembly in the Formation of Induced Mesomorphism in Mixture of ChCl,DTAC, and EG

The multi-component system of cholesteryl chloride (ChCl), dodecyl trimethylammonium chloride (DTAC), and ethylene glycol (EG) exhibits very interesting liquid crystalline mesophases like cholesteric and SmA, SmC, and SmB phases sequentially when the specimen is cooled from its isotropic phase. These phases have been characterized by employing optical and X-ray studies. Pitch of the cholesteric phase has been calculated and discussed. Variation of pitch from the cholesteric phase to smectic phase is smooth and continuous. The temperature variation of optical anisotropy and electrical-conductivity has also been discussed. It has been found that wherever there is a phase transition, the value of electrical susceptibility changes appreciably.     

Time evolution of cholesteric fingers of the second species in an electric field

Different growth modes of isolated cholesteric fingers of the second species (CF‐2) in an electric field at voltages near a coexistence line (V₂) between cholesteric and nematic mesophases are in detail described. Videomicroscopy and computer image analysis were used for investigation of the pattern in polarized light. It is shown how a drift, a lengthening and a shape of fingers depend on the voltage at which the growth sets in and three typical scenarios are distinguished. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Liquid Crystal Properties of Some 3-Arylcholest-2 enes and 3-Arylcholest-3,5-dienes

Abstract

A series of mesogenic 3-arylcholest-2-enes and 3-arylcholest-3,5-dienes were prepared. All members of the monoene and diene steroid series exhibited enantiotropic cholesteric mesophases. The broadest mesophase range was 90°, found for para-methoxyphenylcholest-2-ene.     

Conoscopic image of a biaxial nematic phase in a sodium decyl sulfate – decanol – D2O mixture

ABSTRACT

The nematic phases of a lyotropic system NadS/ decanol/ heavy water are investigated using optical conoscopy and image processing. The phase diagram obtained from these lyotropic materials predicts the occurrence of a direct phase transition, which does not present the biaxial nematic phase, between the discotic (N_D) and calamitic (N_C) nematic phases. A biaxial nematic (N_B) phase is optically characterized and confirmed through conoscopic image, inside the biaxial range, between the two uniaxial nematic phases. Also, their respective transition points are determined by means of image processing. The N_B phase observed here is discussed as part of the nature of the micellar configuration of lyotropic materials which exhibit uniaxial nematic phases.     

Phase Diagrams of Cholesteric and Nematic Thermotropic Liquid-Crystalline Polymers

Linear mesogenic polyesters with flexible spacers (molecular weight ranging from 9,000 to 20,000) are studied by polarized microscopy. The nematic and cholesteric mesophases are identified by means of the contact method. Two enantiomers form perfect solid, cholesteric and liquid solutions. The sign of the twist of the cholesteric phases are determines.     

Optical properties of non‐centrosymmetric mixed crystals K2(La1‐x Cex)(NO3)5 · 2 H2O (x = 0.0 – 1.0)

Large single crystals of optical quality of the non‐centrosymmetric orthorhombic potassium rare earth nitrate mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O were grown at 38 °C from diluted HNO₃. For crystals with x = 0.0, 0.19, 0.38 and 0.66 refractive indices and their dispersion were determined with an error less than 1 · 10^–4 in the wavelength range 0.404 – 1.083 μm by the prism method. Phase matching conditions for collinear SHG frequency conversion were analysed in detail, including calculation of the effective nonlinear optical susceptibility. By an appropriate choice of the fraction x of cerium the mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O allow an adjustment of non‐critical type I phase matching conditions to a desired wavelength of the fundamental wave within the range 1.055(4) – 1.107(6) μm. Non‐critical type II phase matching can be tuned in the wavelength range 0.949(2) – 0.931(2) μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the Orientational Order on the Optical Properties of Cholesteric Liquid Crystals

An orientational order parameter for cholesteric liquid crystals is defined in analogy to nematic mesophases. The influence of this parameter on the selective reflexion and the optical rotatory dispersion is described. Its relative change with temperature is evaluated from ORD measurements for an induced cholesteric soIution and is found to be similar to that known for nematic liquid crystals.     

Amphotropic Properties of Cyclic Scyllitol Hexaesters [1]

Abstract

The new Scyllitol hexaesters with cyclic fragments in lateral substituents of series 1 were synthesized and their thermo- and lyotropic properties (with various organic linear or cyclic solvents) have been studied. It was established that the presence of benzene fragments in the substituents of the scyllitol hexaesters (1a-e) reduces the ability of the mesophase formation. The cyclohexane unit instead (sf. 1f) increases the thermostability of mesophase. While using above mentioned solvents a lot of cases of the induction of mesomorphic properties for non-mesogenic compounds of series 1 have been described. With cyclic solvents lyotropic mesophases were induced in binary mixtures of the hexaester 1a which showed mesomorphic properties neither under thermotropic conditions nor in binary mixtures with linear alkanes.     

Lyotropic nematogenic system potassium laurate-1-decanol-water: Method of synthesis and study of phase diagrams

The results of the study of the potassium laurate-1-decanol-water lyotropic composition are presented. The procedure of preparation of micellar solutions provides the good reproducibility of the phase diagrams. The configurations of the domains of the liquid crystal order are constructed on the concentration plane at the constant temperature as well as the temperature sections (T, C _1-decanol) (at the constant ratio of potassium laurate to water) and (T, C _water) (at the constant ratio of potassium laurate to 1-decanol). The liquid-crystal phases observed are described.     

Synthesis of aromatic liquid crystals with asymmetric diester based on rod-like multi-ring system by two-step esterification method

A novel method of two-step esterifications was developed to synthesize compounds with asymmetric double ester groups. By using this method, six rod-like double ester compounds were prepared with p-hydroxy benzaldehyde, p-hydroxy benzoic acid bicyclohexyl carboxylic acid, cyclohexyl benzoic acid and biphenyl carboxylic acid substituted by n-propyl and n-pentyl as main reactants. The structures and properties of target compounds were confirmed by IR, MS, ¹H NMR, elemental analysis, differential scanning calorimetry (DSC) and hot stage polarizing optical microscope (HS-POM). Typical yields of the target molecules were more than 70%. All the molecules have mesophases with the textures of nematic type, indicating a rod-like molecule with a longer rigid skeleton can keep its mesophases. There was no clearing point observed for any of the derivatives before they decomposed so that the temperature ranges of the mesophases could not be determined. The energy differences between frontier molecular orbitals (HOMO-LUMO) (E_g) of the compounds were calculated by cyclic voltammetry (CV). The terminal ring system has an obvious influence on the energy levels and the energy gaps (E_g).     

“Bands” and “Torsads” Textures in Films and Threads of Hydroxypropyl Cellulose

The present paper deals with films and threads of a mesomorphic cholesteric polymer: the hydroxypropyl cellulose. The steady flow behaviour and the shear induced textures (observed by optical microscopy under crossed polars) of films of lyotropic solutions of this polymer have been studied. A detailed analysis of the banded structures, of either the sheared solutions or the dried films obtained by solvent evaporation, is reported. We point out the existence of transverse striated patterns—“torsads”—superposed on the main banded structures, which are associated with the rewinding of the cholesteric structure following the cessation of the shear stress. The torsads, also observed in some threads, originate from the same relaxation phenomena and are discussed in the last part of the paper.     

Lyotropic Cholestebic Blue Phase

Abstract

Upon carefully cooling a short pitch lyotropic cholesteric phase, made up of disodium cromoglycate, allo-4-hydroxy-?-proline and water, from the isotropic phase, the characteristic platelet texture associated with blue phases is observed.     

Texture transformations and orientational properties of lyotropic nematics in magnetic field

Dynamics of changes of the morphological properties and processes of orientation in lyotropic nematic mesophases by application of external magnetic field have been investigated in detail. The dynamics of changes of the optical birefringence values in nematic‐calamitic mesophase vs. time has been determined. The optical mappings of nonequilibrium magnetically induced textures, which have been observed for this mesophase during orientational process, and changes of birefringence vs. time are presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification of nematic lymoesophases with discotic and cylindrical micelles in lyotropic amphiphilic systems

Nematic lyomesophases with discotic (N _D) and cylindrical (N _C) micelles in complex multicomponent lyotropic systems based on alkyltrimethylammonium bromide detergents have been identified by the ¹H-²H-, and ¹³C-NMR methods and polarizationoptical microscopy. The difference in the structures of the N _D and N _C nematic phases is especially pronounced in the ¹³C-NMR spectra. Addition of chiral dopants to the lyomixture facilitates formation of the Ch _D and Ch _C cholesteric phases. According to the ¹³C-NMR spectra, the micellar mobility in the cholesteric lyomesophases decreases in comparison with the nematic ones. The alignment of lyocholesterics under the action of an external magnetic field is found.     

The Structure of a Lyotropic Liquid Crystalline Phase that Orients in a Magnetic Field

Abstract

The structure of a lyotropic liquid crystalline phase with positive diamagnetic anisotropy (type I), that spontaneously orients in a magnetic field has been studied by means of water NMR quadrupole splittings, NMR diffusion and polarized absorption spectroscopy. It is concluded that this phase is built up of long rodlike aggregates. A preliminary study of a sample with negative diamagnetic anisotropy (type II) shows that this phase probably consists of lamellar aggregates. It is suggested that these phases are suitable as orientation matrices for studies of chromophores with polarized light spectroscopy.