N.M.R. and X-ray diffraction of the 7,7'-disodiumcromoglycate-water lyomesophases

Aqueous solutions of 7,7'-disodiumcromoglycate (7,7'-DSCG) form a variety of mesophases, whose natures depend on concentration and temperature. We have used optical microscopy, N.M.R. (of ²H, ¹⁷O and ²³Na) and X-ray techniques to construct a phase diagram for this system and to characterize the various mesophases. In the concentration range 3 to 25 wt % 7,7'-DSCG four different mesophases are found. On cooling the isotropic solution an opaque gel phase is first obtained, followed on further cooling by a birefringent glassy liquid. At concentrations below 14wt% it is nematic, while at higher concentrations it appears to be a different, more ordered, phase. At lower temperatures a hexagonal phase is formed which finally solidifies on cooling to - 15°C. The N.M.R. and X-ray characteristics of these mesophases are discussed.     

Disc-shaped dinuclear palladium organyls Structure and phase behaviour of charge transfer induced mesophases [1]

Abstract

The recently synthesized non-calamitic/disc-shaped metal organyls containing two palladium atoms and eight flexible side chains represent the first case of metallo-mesogens exhibiting the nematic discotic (N_D) phase [2]. On doping with 2,4,7-trinitrofluorenone (TNF), a strong electron acceptor, the stabilization and/or induction of mesophases was observed. The phase behaviour of these binary systems and the structures of the mesophases displayed by them were studied by means of polarizing microscopy, differential scanning calorimetry, and X-ray scattering.     

Lyotropic Liquid Crystal to Soft Mesocrystal Transformation in Hydrated Salt–Surfactant Mixtures

Hydrated CaCl₂, LiI, and MgCl₂ salts induce self‐assembly in nonionic surfactants (such as C₁₂H₂₅(OCH₂CH₂)₁₀OH) to form lyotropic liquid‐crystalline (LLC) mesophases that undergo a phase transition to a new type of soft mesocrystal (SMC) under ambient conditions. The SMC samples can be obtained by aging the LLC samples, which were prepared as thin films by spin‐coating, dip‐coating, or drop‐casting of a clear homogenized solution of water, salt, and surfactant over a substrate surface. The LLC mesophase exists up to a salt/surfactant mole ratio of 8, 10, and 4 (corresponding to 59, 68, and 40 wt % salt/surfactant) in the CaCl₂, LiI, and MgCl₂ mesophases, respectively. The SMC phase can transform back to a LLC mesophase at a higher relative humidity. The phase transformations have been monitored using powder X‐ray diffraction (PXRD), polarized optical microscopy (POM), and FTIR techniques. The LLC mesophases only diffract at small angles, but the SMCs diffract at both small and wide angles. The broad surfactant features in the FTIR spectra of the LLC mesophases become sharp and well resolved upon SMC formation. The unit cell of the mesophases expands upon SMC transformation, in which the expansion is largest in the MgCl₂ and smallest in the CaCl₂ systems. The POM images of the SMCs display birefringent textures with well‐defined edges, similar to crystals. However, the surface of the crystals is highly patterned, like buckling patterns, which indicates that these crystals are quite soft. This unusual phase behavior could be beneficial in designing new soft materials in the fields of phase‐changing materials and mesostructured materials, and it demonstrates the richness of the phase behavior in the salt–surfactant mesophases.     

Cholesterol-based dimeric liquid crystals: synthesis and mesomorphic behaviour

Chiral non-symmetric dimeric liquid crystals consisting of a cholesteryl ester moiety as chiral entity and a biphenyl aromatic core, interconnected through n-butyl (C₄) or n-pentyl (C₅) parity alkylene spacers, have been synthesized and investigated for their liquid crystalline properties. All the dimers exhibit enantiotropic mesophases. The first member of the dimers having the C₄ central spacer exhibit only the chiral nematic (N*) mesophase, while the higher homologues also show smectic A (SmA) and twist grain boundary (TGB) mesophases. The dimers of the other series containing the C₅ central spacer also have stable SmA, TGB and N* mesophases, except for the first which does not show the TGB phase. Both series of compounds show a weak odd-even effect with terminal alkyl chain substitution, while the spacer length has a marked influence on the phase transition temperatures.     

The SmCPA phase in five-ring bent-core compounds derived from 5-methoxyisophthalic acid

The synthesis and mesophase characterization of a homologous series of five-ring bent-core compounds derived from 5-methoxyisophthalic acid are described. Most of the compounds exhibit a polar antiferroelectric smectic C phase. Replacement of the terminal n-alkoxy chains by n-alkyl carboxylate groups, not only destabilizes the formation of mesophases but induces a calamitic mesophase. However, extension of the arms of the bent-core molecule by a phenyl moiety stabilizes the switchable phase. The mesophases were investigated using a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical methods.     

The phase diagram of the lyotropic nematic mesophase in the TTAB/NaBr/water system

The phase diagram of the nematic mesophase present in the tetradecyltrimethylammonium bromide/sodium bromide/water ternary system was determined. A calamitic nematic mesophase (N_C) was observed which extends to very high concentrations of electrolyte. The order parameters of the surfactant head group in the mesophases were studied by the NMR quadrupolar splitting of the deuterated surfactant. On increasing the temperature of nematic mesophases with low electrolyte concentrations, a phase separation occurs with the formation of a more highly ordered hexagonal phase and an isotropic phase. Diffusion measurements of the isotropic micellar solution by the NMR PFG method were used to estimate hydrodynamic radii at low surfactant concentrations and to study micelle diffusion as the concentration of the surfactant was increased to the liquid crystalline region. At higher surfactant concentrations, the diffusion coefficient reached a limiting value. The calamitic nematic mesophase in this surfactant/electrolyte/water system appears to be formed by long wormlike micelles.     

Preliminary communication 13C CPMAS NMR of 5,10,15,20-tetrakis(4-n-dodecylphenyl)-porphyrin: dynamics of aliphatic chains in discotic lamellar mesophases

Solid state ¹³C CPMAS NMR spectra of 5,10,15,20-tetrakis(4-n-dodecylphenyl)porphyrin (C₁₂ TPP) have been studied to elucidate the microscopic structures and dynamics in the mesophases. The temperature dependence of ¹³C CPMAS NMR in the aliphatic regions is discussed mainly in relation to the phase transitions. The spectra for the aliphatic chains showed remarkable changes with the phase transition from crystal to lower mesophase (M_L) and from lower to higher mesophase (M_L). It was found that the aliphatic chains partially melt in the M_L phase, while they melt totally in the M_L phase. The spectra in the aromatic region did not vary greatly with the transitions from crystal to M_L and from M_L to M_L, which probably means that the molecular D_4h symmetries are distorted in these mesophases, as in the crystal, on the time scale observed by NMR (~kHz).     

Phase structures of a hydrated anionic phospholipid composition containing cationic dendrimers and pegylated lipids

The effect of 4th generation poly(amidoamine) dendrimer (4G PAMAM) present in an anionic phospholipid composition, consisting of hydrogenated soyphosphatidylcholine (HSPC), cholesterol (CH), dicetyl phosphate (DCP), and poly(ethylene glycol) (Mw approximately 2000) derivatized phosphatidylethanolamine (PEG2000-PE), on the hydration and liquid crystalline structure formation was investigated. The optical and polarized light microscopies of the liposomal dispersion obtained from the hydrated lipid composition show two types of birefringent structures (mesophases): plastic, wormlike microstructures and conventional, over-elongated lamellae. Differential scanning calorimetry (DSC) shows an increase in the liquid crystalline phase transition (Tg) of the lipid composition from 60 to 94 degrees C with increasing 4G PAMAM concentrations from 0 to 0.011 mM, respectively. The Tg values of the two microstructures were 68 and 84 degrees C, respectively, indicating that the plastic microstructures were 4G PAMAM/DCP-complexes-rich (alpha mesophases) and the conventional and elongated lamellae were dendrimer-doped HSPC/CH-rich microstructures (beta mesophases). Optical microscopy shows that the alpha mesophases convert into various other types of vesicular structures such as giant unilamellar vesicles and biliquid foams, upon heating above the phase transition temperature of the lipid composition (approximately 60-65 degrees C). The microstructure transformation is a result of an osmotic influx of water and the detergent action of PEG2000-PE present in the lipid composition. The transmission electron microscopy (TEM) images of the liposomal dispersion show particles embedding circular transparent domains that exactly correlate to the theoretical 4G PAMAM/DCP complex sizes, thus, providing evidence of 4G PAMAM interspersed within the two mesophases. Small-angle X-ray scattering (SAXS) measurements indicate that the alpha mesophases are a dendrimer-interlinked, symmetrically undulated lamellar phase and the beta mesophases are dendrimer-doped, occasionally kinked lamellae. An increase in dendrimer concentration in the lipid composition was found to decrease interlamellar spacing. On the basis of optical microscopy, DSC, TEM, and SAXS data, a model of dendrimer-doped mesophase structure and lamellae fusion is proposed. This investigation provides new self-assembled materials for drug/gene delivery and supplements the understanding of mechanisms involved in various biological processes such as membrane fusion, transmembrane permeation, and endocytosis.     

Synthesis and mesomorphic properties of compounds exhibiting the undulated twist grain boundary smectic C* phase

The synthesis and characterization of three homologous series of compounds exhibiting the undulated twist grain boundary smectic C* (UTGB_C*) phase are reported. The chiral mesophases have been obtained using cholesterol as the chiral moiety. Cholestanol and [S]-[+]-octan-2-ol have also been used as the chiral moiety for comparitive purposes. In addition to this novel phase, cholesteric, smectic A, smectic C* and TGB_A phases have also been observed. The mesophases were characterized using a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and measurement of helical pitch.     

Phases and phase transitions in a nematic lyotropic system with a biaxial phase

NMR spectroscopy and optical microscopy have been used to study phase transitions and structure in nematic lyotropic mesophases formed by potassium laurate, decylammonium hydrochloride and water. The different mesophases obtained in a well-defined composition range have been characterized, by deuterium NMR, following the evolution of the D₂O spectra as a function of temperature and of the orientation of the samples with respect to the magnetic field. Wide ranges of biaxiality have been found and the asymmetry parameter of the averaged electrical field gradient tensor on the deuterium of the D₂O molecule has been determined. The presence of the different mesophases has always been confirmed by observing oriented samples under the polarizing optical microscope.     

Effect of lateral substituents on the mesophases formed by some achiral banana-shaped molecules

Several compounds composed of banana-shaped molecules and exhibiting mesophases are reported. The effect of different lateral substituents on the type of mesophase formed is examined and a comparison made with unsubstituted compounds. The mesophases have been characterized using techniques such as polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. The B₂ phase shows antiferroelectric switching behaviour.     

A Morphological Transition of Inverse Mesophases of a Branched‐Linear Block Copolymer Guided by Using Cosolvents

We report here a strategy for influencing the phase and lattice of the inverse mesophases of a single branched‐linear block copolymer (BCP) in solution which does not require changing the structure of the BCP. The phase of the self‐assembled structures of the block copolymer can be controlled ranging from bilayer structures of positive curvature (polymersomes) to inverse mesophases (triply periodic minimal surfaces and inverse hexagonal structures) by adjusting the solvent used for self‐assembly. By using solvent mixtures to dissolve the block copolymer we were able to systematically change the affinity of the solvent toward the polystyrene block, which resulted in the formation of inverse mesophases with the desired lattice by self‐assembly of a single branched‐linear block copolymer. Our method was also applied to a new solution self‐assembly method for a branched‐linear block copolymer on a stationary substrate under humidity, which resulted in the formation of large mesoporous films. Our results constitute the first controlled transition of the inverse mesophases of block copolymers by adjusting the solvent composition.     

Enhancement of the properties and mesophases stability after the electron beam irradiation on a racemic anti-ferroelectric liquid crystalline mixture

The display parameters and the stability of the various mesophases of a newly synthesised racemic mixture of anti-ferroelectric liquid crystals (AFLCs) have been boosted with the help of the electron beam irradiation. The mixture has phase sequence of isotropic–smectic C–smectic C_A crystal. The effective macroscopic polarisation and transition temperatures of the various mesophases of the irradiated mixture have increased as compared with the pure mixture. The macroscopic polarisation of the mixture has increased from 21 to 27 nC/cm² due to the irradiation. From various studies, we have observed that the temperature range of the smectic C_A phase has increased by 20.6°C with marginal decrease in the temperature range of the smectic C phase.     

Design and preparation of liquid crystalline block copolymers

The design and preparation of liquid crystalline (LC) block copolymers by use of azo-macroinitiators are outlined. This approach is very versatile and makes it possible to realize diverse architectures of block copolymers, including non-LC/side-chain, non-LC/main-chain and side-chain/main-chain block copolymers. The different blocks were phase separated and underwent their individual phase transitions. In side-chain/main-chain block copolymers different LC mesophases coexisted in equilibrium.     

Liquid crystalline properties of 4-hexyloxybenzylidene-4'-alkyloxyanilines

The liquid-crystalline polymorphism of the homologous series of 4-hexyloxybenzylidene-4'-alkyloxyanilines is investigated. Basing on the polarization microscopy (POM, TOA), the DSC calorimetry and miscibility studies the following mesophases were detected: nematic, smectic A, smectic C and smectic I. The phase diagrams of the compounds of these series with 4-hexyloxybenylidene-4'-pentylaniline (as the standard of mesophases) show induction of the smectic F mesophases. Their dependence on the alkyl chain length and mole fraction is shown.     

Dimesogenic liquid crystal consisting of cholesterol and Schiff base moieties: dependence of LC properties on the spacer length and fluorination of the alkoxy tails

The liquid crystalline properties of two series of non-symmetric liquid crystal dimers consisting of cholesterol and Schiff base moieties interconnected by ω-oxyalkanoyl spacers of varying length are compared: one series (SBOC- n ) carry the octyloxy tail on the Schiff base mesogen, and the other (SBOF- n ) a perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited mesophases over a much wider temperature range than those with the alkoxy tail. The latter series favoured the formation of more diverse mesophases than the former. SBOC-4, -5 and -7, and SBOF-4, -5 and -10 formed the chiral smectic C phase.     

New Lyotropic nematic phases with unusual anisotropies of magnetic susceptibility: Type I DM and type II CM

Two lyotropic mesophases of opposite signs of susceptibility anisotropy have been found, one a quaternary and the other a ternary phase. Conclusive evidence is presented that the disk-micelle mesophase has positive diamagnetic anisotropy and the rod-like micelle phase has negative anisotropy. These have been named type I DM and type II CM mesophases respectively to conform with the notation previously introduced for mesophases based on aliphatic chain surfactants.     

Rapid Phase Transitions of Thermotropic Glycolipid Quasicrystal and Frank-Kasper Mesophases: A Mechanistic Rosetta Stone

Experimental results are presented that serve to lower the barrier for developing the science and technology of non-classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank–Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar-polyolefin conjugates. By employing “alloys” comprised of mono- and disaccharide-polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid-like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain-induced introduction of planar defects into the A15 lattice.     

Novel smectic liquid crystals based on benzo[c]cinnoline: their synthesis,mesomorphism, opto- and electro-chemical properties

A series of novel calamatic liquid crystals based on a polar benzo[c]cinnoline moiety were efficiently prepared through a facile route. Rich smectic mesophases were induced by the monoalkylated and dialkylated molecular design, including highly ordered smectic mesophases in the rectangular and hexagonal orders. Dialkylated phenylbenzocinnoline derivatives showed a very wide temperature range over 150°C for smectic C (SmC) phase, while the monoalkylated ones only presented the low-ordered mesophases, which exhibited a bilayer structure in crystalline phase. From pronounced reversible redox waves in a cyclic voltammogram and low-lying lowest unoccupied molecular orbital level of about ?3.2 eV indicated possible electron-transporting behaviour. In addition, a switching behaviour originating from ferroelectricity in SmC* induced by chiral dopant was observed.     

Some remarks on the evolution of research into the structures of mesogens and mesophases

Research on mesogens and mesophases began with the surprising observation of a fluid and birefringent phase formed by a pure compound having a calamitic (rod-like) molecule. The structures of the smectic A, nematic and cholesteric phases which emerged after this discovery were elucidated essentially by observations with a polarizing microscope. Smectic polymorphism was also established by microscopic observations. The structures of the different smectic mesophases previously predicted theoretically, was then obtained further type of purposely designed mesophase was the pyramidic type, also exhibiting a rich polymorphism. Research on mesogens and mesophases is a field in continuous expansion. main historical results on the are listed here. The discotic mesophase, and its polymorphism observed. A