The effect of substituent position on the liquid crystalline properties of dodecyl-D-xylitols

Recently we have been concerned with a systematic and fundamental investigation into the effects of the linking group on the lyotropic and thermotropic properties of aliphatic substituted acyclic carbohydrate systems. For this purpose, we chose to study the selfassembling behaviour of alkyl substituted xylitols where the aliphatic chain was attached to the xylitol moiety via ether, ester and thioether linkages. We have extended this work and, in this current study, we report the effects on the self-assembling properties of sequentially moving the position of a dodecyl chain in acyclic x-O-dodecyl-D-xylitols. This work was used for a direct comparison with results reported on cyclic systems such as the dodecyl x-O-beta-Dglucopyranosides.     

Hydrophobic and Hydrophilic Balance and Its Effect on Mesophase Behaviour in Hydroxyalkyl Ethers of Methyl Glucopyranoside

Four series of monosubstituted methyl α‐D ‐glucopyranoside hydroxyalkyl ethers were prepared and their thermotropic and lyotropic self‐organising properties were investigated in terms of the hydrophobic–hydrophilic balance with respect to their molecular structures. The results obtained lead us to a new understanding of the forces that drive the formation of condensed soft‐matter phases.     

Amphiphilic N-benzoyl-1-amino-1-deoxy-D-glucitol derivatives forming thermotropic lamellar, columnar and different types of cubic mesophases

Novel amphiphilic glucamine derivatives have been synthesized. These are N-benzoyl-1-deoxy1-methylamino-D-glucitols and N-benzoyl-1-amino-1-deoxy-D-glucitols carrying one, two or three aliphatic chains (CnH2n 1O- with n 3, 6 and 12) grafted to the benzamido group. The thermotropic mesophases of these compounds were studied by thermal polarizing optical microscopy and differential scanning calorimetry, and some also by X-ray scattering. Depending on the number and the length of the alkyl chains lamellar, bicontinuous cubic, hexagonal columnar or inverted micellar cubic mesophases were detected by analogy with lyotropic systems. In the contact region between lamellar phases of the single chain amphiphiles and micellar cubic phases of the mesomorphic triple chain compounds, hexagonal columnar phases can be induced. A hexagonal columnar phase was also induced in the contact region between a bicontinuous and a micellar cubic mesophase. The lyotropic liquid crystalline behaviour of the dodecyloxy substituted N-benzoyl-1-deoxy-1-methylamino-D-glucitols was investigated by the solvent penetration method using ethylene glycol as protic solvent. On increasing the solvent content, the double chain compound forms a cubic and a lamellar mesophase and the triple chain compound forms a hexagonal columnar lyomesophase. The dodecyloxy substituted compounds were also investigated with respect to their behaviour as thin films at the air-water interface using a Langmuir film-balance. Different types of pi/Aisotherms were observed whereby the molecular areas at collapse were determined either by the size of the carbohydrate head group (single chain compounds) or by the number of alkyl chains (double and triple chain compound).     

Orientational order in smectic liquid-crystalline phases of amphiphilic diols

The thermotropic smectic phases of amphiphilic 2-(trans-4-n-alkylcyclohexyl)-propane-1,3-diols were investigated by means of small- and wide-angle x-ray scattering and values of the smectic (bi-)layer spacing, the orientational order parameters P(2) and P(4), the orientational distribution function as well as the intralayer correlation length were extracted from the scattering profiles. The results for the octyl homolog indicate that these smectic phases combine a very high degree of smectic one-dimensional-translational order with remarkably low orientational order, the order parameter of which (P(2) approximately 0.56) is far below those values typically found in nonamphiphilic smectics. This combination, quite exceptional in thermotropic smectics, most likely originates from the intermolecular hydrogen bonding between the terminal diol groups which seems to be the specific driving force in the formation of the thermotropic smectic structure in these amphiphiles and leads to a type of microphase segregation. Even in the absence of a solvent, the liquid-crystalline ordering of the amphiphilic mesogens comes close to the structure of the so-called neat soaps, found in lyotropic liquid crystals.     

Assembly of a model hydrophobic drug into cationic bilayer fragments

Catanionic surfactants result from the pairing of oppositely charged amphiphilic molecules, forming a new class of surfactant molecules with various interesting lyotropic and thermotropic properties. With the aim of probing the role of both headgroup chemical nature/structure and molecular shape, a series of catanionic surfactants were synthesized. The cationic portion of the molecule is kept constant, being the dioctadecyldimethylammonium double chain. Different single-chained surfactants with varying headgroups and chain lengths are used as the anionic pair. The thermotropic behavior has been studied by DSC and the mesophase structural investigated by polarized light microscopy. The results indicate that, for a given chain length, parameters such as headgroup polarity and charge density, as well as volume, influence the catanionic surfactant behavior. The thermodynamic parameters are qualitatively evaluated, considering the headgroup chemical nature and the overall molecular structure.     

The thermotropic and lyotropic liquid-crystalline properties of acetoacetoxypropyl cellulose

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid-crystalline phases. DSC and hot-stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ₀ of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x-ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ₀ for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.     

Liquid crystals and life

The molecules of living systems invariably exhibit both thermotropic and/or lyotropic liquid crystalline properties. In some cases the mesophases formed by bio-materials have lamellar structures, whereas in other situations they form columnar phases. Many liquid crystal biomaterials are found in cell membranes, indicating that such structures have properties that are dependent on liquid crystallinity for their behaviour of a variety of bio-materials is discussed. function. In this article the mesomorphic     

Glasses of new 2,3,9,10,16,17,23,24-octasubstituted phthalocyanines forming thermotropic and lyotropic discotic mesophases

The synthesis and mesogenic properties of a new class of liquid crystalline metal-free and metalated phthalocyanines with different numbers of alkylthio side chains are presented. The effect of the substitution pattern in a series of differently octasubstituted phthalocyanines on the width and order of the thermotropic mesophase is investigated. The exchange of the alkylthio groups from chlorine atoms alters the mesophase width and the melting behaviour. Glassy phthalocyanines, without any tendency to crystallize, can be synthesized in this way. Furthermore, mixtures of differently 4,5-disubstituted benzenedicarbonitriles are tetramerized statistically to the corresponding mixtures of substituted phthalocyanines. The effect of decreasing symmetry at the molecular level on the properties of the liquid crystalline materials has been investigated. Highly oriented columnar systems can be obtained with these mixtures. For all compounds containing less than eight alkylthio groups, lyotropic mesomorphism in hexadecane solution is also found.     

Amphitropic liquid crystals. Two lamellar phases in a surfactant containing thermotropic and lyotropic mesogenic groups

We have studied the lyotropic liquid-crystalline behaviour of cationic surfactants containing a potentially thermotropic moiety, a terminal cyanobiphenyloxy group. Both mono-alkyl and mid-chain substituted dialkyl surfactants have been examined using optical microscopy and NMR spectroscopy. Incorporation of the cyanobiphenyloxy group destabilizes the hexagonal and bicontinuous cubic phases, with only an extensive lamellar region being observed. For the dialkyl surfactant there is a range of compositions where two lamellar phases co-exist, one water-rich and the second surfactant-rich.     

On the structure of the thermotropic cubic mesophases

Two new substances, glycosides, with an optically isotropic mesophase were investigated. Using measurements of the refractive index, the optical isotropy of the thermotropic phases was proved. X-ray diffraction experiments provided information about the structure of the cubic mesophase. Similarly to the lyotropic cubic phases, here too structures of space group la-3d are present.     

Electrical conductivity of lyotropic and thermotropic ionic liquid crystals consisting of metal alkanoates

The electrical properties of ionic smectic liquid crystal (ISLCs), specifically, (i) oriented and non-oriented samples of lyotropic ISLC potassium caproate and (ii) oriented samples of thermotropic ISLC cobalt decanoate, are investigated in detail. The electrical conductivity of lyotropic smectic potassium caproate is higher than that of isotropic electrolytes. A giant anisotropy in the electrical conductivity of oriented samples of thermotropic ISLC cobalt decanoate is observed. The mobility of charge carriers in lyotropic ISLC is measured for the first time. The unusual electrical properties of ISLCs, which are governed by their layered structure, show that they have application potential in optoelectronic devices.     

The dependence of mesomorphic behaviour on the extent of hydrogen-bonding in sugar derived polyols

The thermotropic liquid crystalline properties of a variety of chiral and racemic dodecyloxy substituted polyols derived from carbohydrates were investigated as a function of the number of hydroxyl groups associated with the polyol unit. It was found that all of the materials exhibited smectic A* phases, and that the clearing points increased monotonically with the number of hydroxyl groups. The linear increase was found to be independent of stereochemical structure and the degree of optical purity. A model suggesting that the smectic A* phase has an internal microphase separated structure can be used to account for these observations.     

Theory of Liquid-crystalline Ordering in Polymer Brushes

Summary: We present a review of the works devoted to investigation of LC ordering in polymer brushes. This series has been carried out by the group of T. M. Birshtein and covers the following aspects of the problem: thermotropic LC phase transition in LCP brushes, microphase segregation, homeotropic and planar LC phases, LC polymer in LC solvent, lyotropic LCP brushes, LC transitions under normal or lateral force (shear flow). Analytical theory is developed for simplified model of polymer brush with accounting for thermotropic attraction in Mayer-Saupe approximation and lyotropic repulsion in DiMarzio formalism; numerical calculations are fulfilled in self-consistent field approximation (method of Scheutjens and Fleer). Brownian dynamics simulations are applied for modeling polymer brush in a shear flow.     

Emulsions with structured continuous phases

Recent research on the role of the continuous phase in emulsions is reviewed. Special attention is given to the structured continuous phases such as lyotropic and thermotropic liquid crystals and gel networks. The implications in the formation, stability and properties of emulsions are discussed. Some recent applications, particularly in templating for the preparation of new materials, are also introduced.     

Amphitropic liquid crystals. Two lamellar phases in a surfactant containing thermotropic and lyotropic mesogenic groups

Abstract

We have studied the lyotropic liquid-crystalline behaviour of cationic surfactants containing a potentially thermotropic moiety, a terminal cyanobiphenyloxy group. Both mono-alkyl and mid-chain substituted dialkyl surfactants have been examined using optical microscopy and NMR spectroscopy. Incorporation of the cyanobiphenyloxy group destabilizes the hexagonal and bicontinuous cubic phases, with only an extensive lamellar region being observed. For the dialkyl surfactant there is a range of compositions where two lamellar phases co-exist, one water-rich and the second surfactant-rich.     

Polarizing-alignment layers for twisted nematic cells

We describe polarizing films formed from the lyotropic liquid crystalline phases of dyes dissolved in water. The dye polarizers possess a high dichroic ratio close to that of conventional polarizers. In addition, the dried dye films provide a uniform homogeneous orientation for thermotropic nematic materials. Therefore, thin dye films can simultaneously serve as internal polarizers and as alignment agents. These properties make them especially suitable for twisted nematic devices based on low cost birefringent plastic substrates.     

Polarizing-alignment layers for twisted nematic cells

We describe polarizing films formed from the lyotropic liquid crystalline phases of dyes dissolved in water. The dye polarizers possess a high dichroic ratio close to that of conventional polarizers. In addition, the dried dye films provide a uniform homogeneous orientation for thermotropic nematic materials. Therefore, thin dye films can simultaneously serve as internal polarizers and as alignment agents. These properties make them especially suitable for twisted nematic devices based on low cost birefringent plastic substrates.     

Crystal Smectic-B Phase from a Mesomorphic Ferrocene Derivative

The thermal properties of two ferrocene derivatives, substituted by either one or two cholesteryloxycarbonyl units, were investigated. While the monosubstituted ferrocene derivative 1 was found to be non-mesomorphic, the disubstituted ferrocene derivative 2 exhibited a crystal smectic-B phase. This result shows that ferrocene-containing thermotropic liquid crystals, despite the bulkiness of the metallocene core, are not limited to disordered calamitic phases.     

Polymorphism and mesomorphism of oligomeric surfactants: effect of the degree of oligomerization

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.     

Structural studies of a new series of biforked mesogens derived from 3,4 dialkoxy cinnamic acid and 3-(3,4 dialkoxy-phenyl) propanoic acid

Structural studies of selected homologues of some new series of biforked mesogens have been performed by X-ray diffraction methods. These series exhibit a thermotropic mesomorphism which shows some similarities with lyotropics. We have identified three different mesophases with large three dimensional lattice cells (i.e. body centred cubic, hexagonal and rhombohedral). The occurrence of such mesophases is related to the core flexibility; moreover, the chain to core length ratio is one of the main parameters that drive the thermotropic polymorphism, playing a role similar to that of the solvent concentration in a lyotropic system. However the symmetries as well as the lattice constants, in units of molecular size, appear to be different in the two cases owing to differences in their chemical architecture.