Lyotropic Liquid Crystal Phases Research Articles

Micellar-shape anisometry near isotropic-liquid-crystal phase transitions.

Micellar phases of the sodium dodecyl (lauryl) sulfate (SLS)--water--decanol system have been studied by x-ray scattering in the isotropic (I) phase, with emphasis on the I\ensuremath{\rightarrow}hexagonal (${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$) and I\ensuremath{\rightarrow}nematic-cylindrical (${\mathit{N}}_{\mathit{c}}$) lyotropic liquid-crystal phase transitions. Analysis of the scattering curves is made through modeling of the product P(q)S(q), where P(q) is the micellar form factor and S(q) is the intermicellar interference function, calculated from screened Coulombic repulsion in a mean spherical approximation. Results show that micelles grow more by decanol addition near the I\ensuremath{\rightarrow}${\mathit{N}}_{\mathit{c}}$ transition (anisometry \ensuremath{\nu}\ensuremath{\simeq}3) than by increased amphiphile concentration in the binary system near the I\ensuremath{\rightarrow}${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$ phase transition (\ensuremath{\nu}\ensuremath{\simeq}2.4). These results compare well with recent theories for isotropic--liquid-crystal phase transitions.

Monomeric and oligomeric quaternary ammonium derivatives of cholesterol: Concentrated and dilute aqueous solution phase behaviour

Five polymerizable and another seven non-polymerizable quaternary ammonium derivatives of cholesterol have been synthesized, and their dilute and concentrated aqueous solution phase behaviour characterized. Electrical conductivity measurements have shown that all the species form small aggregates at concentrations < 10 −4 M, and it seems likely that these have structures similar to those formed by bile acid salts. Surface tension measurements suggest that these molecules do not adsorb spontaneously at an air-water interface. None of the species display thermotropic liquid crystal properties but all form lyotropic liquid crystal phases at high concentration (>0.2 M). The “gel” to liquid crystal transition temperature is typically ∼ + 40°C. The five methacrylate derivatives have been oligomerized to form saturated species with DP n in the range 25–180. These oligomers also form a lamellar phase in water, and the three with the cationic headgroup attached close to the cholesterol nucleus display a transition temperature similar to the monomers. Two oligomers with a C 10 linear hydrocarbon spacer between the headgroup and the nucleus yield an elevated (+20°C) transition temperature, probably because the spacer reliefs steric compression and allows closer packing of the hydrophobes in the “gel” state.

Microscopy, x-ray diffraction, and NMR studies of lyotropic liquid crystal phases in the C22EO6/water system: a new intermediate phase

Mixtures of the nonionic surfactant hexaethylene glycol cis-13-docosenyl ether (C 22 EO 6 ) with water ( 2 H 2 O) were by optical microscopy, small-angle X-ray scattering, and 2 H NMR spectroscopy. A schematic phase diagram has been obtained, which shows two high-temperature bicontinuous cubic phases (V 2 ) and a low-temperature fluid intermediate phase (Fl) in addition to the usual hexagonal (H 1 ) and lamelIar (L α ) phases

Influence of solvent-headgroup interactions on the formation of lyotropic liquid crystal phases of surfactants in water and nonaqueous protic and aprotic solvents

Influence of solvent-headgroup interactions on the formation of lyotropic liquid crystal phases of surfactants in water and nonaqueous protic and aprotic solvents

Micellar hexagonal phases in lyotropic liquid crystals.

The hexagonal cell parameter a of the system sodium dodecyl lauryl sulfate and water as a function of volume concentration ${\mathit{c}}_{\mathit{v}}$ in phase ${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$ shows the functional behavior expected for micelles of finite length: a\ensuremath{\propto}${\mathit{c}}_{\mathit{v}}^{\mathrm{\ensuremath{-}}1/3}$. The interpretation of x-ray data based on finite micelles leads to an alternative description of the hexagonal phase ${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$: spherocylindrical micelles of constant radius with length that may grow along the range of the ${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$ phase. Results are compared with recent statistical-mechanical calculations for the isotropic I-${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$ transition. The absence of diffraction in the direction perpendicular to the hexagonal plane is ascribed to polydispersity of micellar length, which also is a necessary condition for the occurrence of direct I-${\mathit{H}}_{\mathrm{\ensuremath{\alpha}}}$ transitions.

Structure of Films Formed from Lyotropic Liquid Crystal Phases of Dyes. 1. Benzopurpurin - 4B

Abstract The films aligned by drawing thin lyotropic liquid crystal layers of benzopurpurin-4B were investigated by X-ray and electron diffraction methods. The analysis of diffraction data was carried out by straigh-forward (Patterson synthesis) and model procedures. The film structure is crystalline on the microlevel. Molecules ar packed in monoclinic lattice (a=27A, b=7. 2Å, c=59.5Å, β =141°) corresponding to space group C2/c. This model explains the type geometry of molecular aggregates in the lyotropic liquid crystal phase of benzopurpurin-4B.

Lyotropic liquid crystal phase formation in l-(alkanoylmethyl amino) 1-deoxy-D-glucitols

Abstract The lyotropic and thermotropic liquid crystals of a series of 1-(alkanoylmethyl amino) 1-deoxy-D-glucitols (C8–C12, C18=) oleoyl derivative) have been investigated by polarizing optical microscopy and differential scanning calorimetry. For chain lengths longer than the octanoyl derivative, the pure compounds form a lamellar (smectic A) phase before melting to the isotropic liquid. Both the liquid crystal and isotropic phases of the neat surfactant and aqueous mixtures supercool to form metastable states. In water the octanoyl derivative forms hexagonal (H1) phase, while the C8–C12 compounds give H1, cubic (V1) and Lα mesophases. Only the Lα phase is observed with the oleoyl derivative.

Rigid-Rod And Segmented Rigid-Rod Polyimides: GEL/SOL And Liquid Crystalline Transitions, Fibers And Films

ABSTRACTOrgano-soluble rigid-rod and segmented rigid-rod polyimides and their copolyimides exhibit isotropic solutions in hot m-cresol, but form gels upon cooling. A lyotropic liquid crystal phase is observed below the gel/sol transition. Mechanical gel formation is caused by liquid-liquid phase separation, while the liquid crystal phase may be formed through a nucleation process after gelation. High performance fibers can be spun from the hot isotropic solutions using a dry-jet wet spinning method. After the fibers are drawn at high temperatures, they display tensile strength higher than 3.2 GPa and an initial modulus higher than 130 GPa. In particular, the fibers retain relatively high mechanical properties at elevated temperatures. Solution casted films exhibit very low thermal expansion coefficients and dielectric constants. Their structure, morphology and property relationships will also be discussed.

Does Shear-Flow Enhance or Suppress Fluctuations in Shectics?

AbstractWe investigate the effects of shear-flow on the smectic phase of thermotropic and lyotropic liquid crystals. We show that shear-flow transforms a Smectic-A thermotropic into an orthorombic solid by the suppression of undulation fluctuations. In contrast, the lyotropic Lαphase exhibits, in addition, a very striking enhancement of shortwavelength concentration fluctuations - a phenomenon which is closely analogous to a well-known effect in polymer solutions. We demonstrate this result using both hydrodynamic theory as well as a microscopic model based on the Helfrich theory of membranes. The dispersion relation of the concentration fluctuations is in qualitative agreement with recent experiments on the Lαphase in shear flow.

Volume constriction in a lipid-water liquid crystal using high-pressure x-ray diffraction.

We report a measurement of the change in the total volume of a biological lipid-water system when water molecules are removed from the fully hydrated lyotropic liquid-crystal phase, where the water molecules are near a polar interface, to the surrounding bulk water. The commonly used assumption of linear additions of constituent volumes predicts that the water mole fractions of these lipid-water phases should be independent of hydrostatic pressure. The discrepancy between this prediction and our high-pressure x-ray-diffraction measurements is due to a decrease of 0.1 A${\mathrm{\r{}}}^{3}$ in the total volume of the system per molecule of water incorporated into the fully hydrated lipid-water aggregate from the bulk water.

Structure of 3,4,5-trihydroxybenzoic acid octyl ester (octyl gallate) dihydrate at 123 K. A non-mesogenic amphiphilic molecule

The crystal structure of 3,4,5-trihydroxybenzoic acid octyl ester (octyl gallate) dihydrate, C15H22O5.2H2O, is triclinic, P1, with a = 6.617 (1) [6.648 (1)], b = 9.956 (2) [9.995 (3)], c = 14.088 (4) [14.327 (7)] A, alpha = 79.08 (2) [79.78 (3)], beta = 85.58 (3) [86.59 (4)], gamma = 70.80 (2) [70.99 (3)] degrees, V = 860.5 A3, Z = 2, Dx = 1.229 1.229 [1.183] g cm-3, lambda(Mo K alpha) = 0.7093 A, mu = 0.58 cm-1, F(000) = 344 at 123 K [290 K]. The structure was solved by direct methods and refined to R(F2) = 0.059 for 302 parameters and 3655 observations. The alkyl chain of the molecule is in the fully extended conformation. The molecular packing is head-to-head bilayer with interdigitizing alkyl chains. The gallate head groups are hydrogen bonded with the water molecules to form a strong system of intra- and intermolecular hydrogen bonds consisting of finite and infinite chains. The crystals undergo crystal-to-crystal phase transitions at 365 K on heating and at 333 K on cooling, but despite the molecular packing which is analogous to that of the mesogenic alkyl glycosides, there is no thermotropic liquid crystal phase prior to the formation of the isotropic liquid phases at 376 K. Similary, no lyotropic liquid crystal phases are observed at room temperature in contact with a mixture of water and propanediol in which the crystals are soluble.

First-order transition between nematic phases in lyotropic liquid crystals

Abstract Experimental evidence for the existence of a first order transition between Nc–Nd uniaxial lyonematic phases as a function of the variable M d (number of decanol molecules per amphiphilic molecule) is reported. The relevance of this evidence to molecular models for micellar aggregates is discussed. The evidence is for a change in micellar symmetry at this transition.

Model for lamellar phases of interacting lipid membranes.

We solve in mean-field approximation a model describing the lamellar phases of lyotropic liquid crystals as stacks of interacting bilayer membranes. The model is a synthesis of a Landau-Ginzburg theory of membrane-melting transitions and a continuum treatment of the molecular forces acting between bilayers. The resulting phase diagrams include both planar and modulated phases and are in semiquantitative agreement with experimental observation on neutral lipids. The approach highlights the role of interactions in the thermodynamic behavior of membrane systems.

Geometrical aspects of the frustration in the cubic phases of lyotropic liquid crystals.

Bicontinuous cubic phases, composed of bilayers arranged in the geometries of periodic minimal surfaces, are found in a variety of different lipid/water systems. It has been suggested recently that these cubic structures arrive as the result of competition between two free-energy terms: the curvature energy of each monolayer and the stretching energy of the lipid chains. This scenario, closely analogous to the one that explains the origin of the hexagonal phases, is investigated here by means of simple geometrical calculations. It is first assumed that the lipid bilayer is of constant thickness and the distribution of the (local) mean curvature of the phospholipid-water interfaces is calculated. Then, assuming the mean curvature of these interfaces is constant, the distribution of the bilayer's thickness is calculated. Both calculations quantify the fact that the two energy terms are frustrated and cannot be satisfied simultaneously. However, the amount of the frustration can be smaller for the cubic phase than for the lamellar and hexagonal structures. Therefore, this phase can appear in the phase diagram between the other two, as observed in many recent experiments.

Defects in flexible membranes with crystalline order.

We study isolated dislocations and disclinations in flexible membranes with internal crystalline order, using continuum elasticity theory and zero-temperature numerical simulation. These defects are relevant, for instance, to lipid bilayers in vesicles or in the ${L}_{\ensuremath{\beta}}$ phase of lyotropic smectic liquid crystals. We first simulate defects in flat membranes, obtaining numerical results in good agreement with plane elasticity theory. Disclinations and dislocations eventually exhibit a buckling transition with increasing membrane radius. We generalize the continuum theory to include such buckled defects, and solve the disclination equations in the inextensional limit. The critical radius at which buckling starts to screen out internal elastic stresses is determined numerically. Computer simulation of buckled defects confirms predictions of the disclination energies and gives evidence for a finite dislocation energy.

Liquid Crystal Formation of Poly(γ-n-Alkyl D-Glutamate)S Having Long Alkyl Side Chains

Abstract Poly(γ-n-alkyl D-glutamate)s having alkyl side chains longer than decyl form a cholesteric liquid crystal phase in the solutions of helicogenic solvents. In the lower temperature range, the side chains of these polymers more or less crystallize, and above the melting temperature of the side chain crystallites the polymers are assumed to be in liquid crystalline state. It was found that these polymers form both lyotropic and thermotropic liquid crystal phases.

Complete unbinding and quasi-long-range order in lamellar phases.

Lamellar phases of lyotropic liquid crystals can be swollen by addition of solvent. Such a process, which leads to a strong increase of the mean interlamellar separation l\ifmmode\bar\else\textasciimacron\fi{}, can be viewed as a phase transition, termed complete unbinding. Starting from the microscopic interaction for a pair of lamellae, we derive an effective model for the multilayer phase. We predict a power-law increase of l\ifmmode\bar\else\textasciimacron\fi{}, and show that the system exhibits quasi-long-range translational order characterized by an exponent ${X}_{m}$, which is either universal or, for sufficiently long-range repulsive interactions, depends on molecular details.

Kinetics of Lyotropic Liquid Crystal Phase Transitions: A Time Resolved X-Ray Diffraction Study

Abstract Phase transitions in the fully saturated monogalactosyldiacylglycerol in water system have been studied using time resolved x-ray diffraction. Three mechanisms for phase transitions are identified in these studies and can be correlated with the transit times involved in the transformations. The relationship between these observations and previous reports on phospholipid and surfactant phase transitions is discussed.

A Study of the Angular Dependence of NMR Relaxation Times in Macroscopically Oriented Lyotropic Liquid Crystal Lamellar Phases

Abstract The angular dependence of 1H and 2H NMR relaxation rates has been investigated for macroscopically oriented multi-bilayers of egg yolk lecithin and dimyristoyl lecithin in the Lα phase. Proton T ip values show a strong dependence on the orientation of the bi-layer normals to the magnetic field, while deuterium T ip and T 1 values and proton T 1's show little or no orientation dependence. The results are interpreted on the basis of a simple modification of the theory of Ukleja, Pirs and Doane for relaxation in oriented thermotropic phases. The results confirm the presence of collective fluctuations in the density of lipid packing in the plane of the bilayer which dominate proton relaxation at low frequencies. There is no evidence of a significant contribution from collective order fluctuations.

Composition and fractionation within conjugated isotropic and anisotropic phases of lyotropic liquid crystals

Composition and fractionation within conjugated isotropic and anisotropic phases of lyotropic liquid crystals