Showing papers on "Lyotropic liquid crystal published in 1994"
169 citations
TL;DR: The phase diagram has been delineated between 28% and 70% by weight of surfactant as mentioned in this paper, and a wide range of "intermediate" behavior including a defected lamellar phase (L α H ), a nematic phase of rod micelles (N C ), and cubic or intermediate phases depending upon sample history.
Abstract: Mixtures of the nonionic surfactant hexaethylene glycol n-hexadecyl ether, C 16 EO 6 , and water were examined by optical microscopy, 2 H NMR, and small-angle X-ray and neutron scattering. The phase diagram has been delineated between 28% and 70% by weight of surfactant. Besides the conventional lamellar, L α , and hexagonal H 1 , phases, the system exhiibits a wide range of «intermediate» behavior including a defected lamellar phase (L α H ), a nematic phase of rod micelles, (N C ), and cubic or intermediate phases depending upon sample history, which both occur in the same region of the phase diagram
95 citations
43 citations
TL;DR: In this article, the flow-induced structures of three types of lyotropic liquid crystals with different degrees of flexibility are investigated during simple shear flow using both optical microscopy and small angle light scattering.
Abstract: The flow-induced structures of three types of lyotropic liquid crystals with different degrees of flexibility are investigated during simple shear flow. Both optical microscopy and small angle light scattering are used. Different types of structure appear systematically in shear rate regions that can be associated with specific regions of the rheological curves. Changing concentration and temperature does not affect the correlation between rheological and textural transitions. Stress and texture have also been observed in transient experiments when starting from a monodomain. The types of texture that occur at different shear rates under steady state conditions can also be observed as transient structures at a single shear rate.
40 citations
TL;DR: In this paper, the effect of added non-adsorbing polymer on the isotropic-nematic phase transition in a model lyotropic liquid crystal was studied theoretically.
Abstract: The effect of added non-adsorbing polymer on the isotropic-nematic phase transition in a model lyotropic liquid crystal - a suspension of hard rods - is studied theoretically. The results indicate that the transition is widened and that polymer is partitioned preferentially into the more dilute isotropic phase. The concentration of polymer where a noticeable effect on the transition starts to occur is predicted to be of the order 5% of the coil overlap threshold c *
25 citations
TL;DR: In this article, the state of water and several thermal transitions were examined in several surfactant/water lyotropic liquid crystalline systems, including Aerosol OT (AOT), didodecyldimethylammonium bromide (DDAB), dioctadecyl-dimethylamethylammium-bromide(DODAB) and M-decylphosphonic acid (DPA), and three types of water were detected: bulk-like, interfacial and hydration water.
23 citations
TL;DR: In this paper, a homologous series of double-chain non-ionic surfactants with the general formula (Cn)2 GEmM, where Cn denotes an alkyl chain, G a triglyceryl, and EmM an oligo-oxyethylene mono-methyl ether are synthesized withn=6-8 andm=6, 8, 10.
Abstract: A homologous series of double-chain non-ionic surfactants with the general formula (Cn)2 GEmM, where Cn denotes an alkyl chain, G a triglyceryl, and EmM an oligo-oxyethylene mono-methyl ether are synthesized withn=6–8 andm=6, 8, 10. The branched hydrophobic part of the surfactants introduces a large cross-section of the lipophilic surfactant moiety that is directly reflected in the shape of the micelles and the LC phase behavior in aqueous solution. The phase behavior of these V-amphiphiles is investigated with polarizing microscopy and x-ray diffraction and reveals that the branched lipophilic part strongly stabilizes the lamellar mesophase. This is in agreement with established packing models.
22 citations
TL;DR: In this article, the supermolecular structure of thin films of poly{5,7-dodecadiyne-1,12-diol bis[((4-butoxycarbonyl)methyl)urethane]) (P-4-BCMU), a soluble polydiacetylene, and mixtures of two P-4BCMUs with different average lengths of molecules were investigated by means of TEM.
Abstract: The supermolecular structure of thin films of poly{5,7-dodecadiyne-1,12-diol bis[((4-butoxycarbonyl)methyl)urethane]) (P-4-BCMU), a soluble polydiacetylene, and mixtures of two P-4-BCMUs with different average lengths of molecules were investigated by means of TEM. An extended-chain lamella is observed in thin films of the polymer and mixtures. The influences of the weight fraction of a component and the difference between the average lengths of molecules on the supermolecular structure are discussed. Models describing structural features of extended-chain lamellae for the polymer and mixtures are suggested. The chain segregation according to the distribution of the extended-chain length of the rodlike macromolecules and the formation of the extended-chain lamella are discussed
20 citations
TL;DR: In this paper, the dynamics of textural evolution in PBLG with homeotropic alignment have been studied in detail at relatively low shear rates, showing that textural patterns are explained by considering the appropriate balance of the elastic forces in the liquid crystal against the viscous forces due to shear flow.
Abstract: Starting with large monodomain samples of PBLG with homeotropic alignment, the dynamics of textural evolution have been studied in detail at relatively low shear rates. A wide variety of textural patterns are seen which are explained by considering the appropriate balance of the elastic forces in the liquid crystal against the viscous forces due to shear flow. Textural evolution depends on shear rate and sample thickness
17 citations
TL;DR: In this article, the effect of hexagonal liquid crystal phases produced with quaternary ammonium surfactants on the textural ordering of silica gels is examined, and the structural evolution of the material from the starting sol to the thermally treated gel is studied using low angle X-ray diffraction.
Abstract: The use of lyotropic liquid crystal phases is a promising tool in tailoring the porous structure of inorganic gels. In this work, we examine the effect of hexagonal liquid crystal phases produced with quaternary ammonium surfactants on the textural ordering of silica gels. The sol-gel polymerization of the silicon alkoxide precursor (tetramethoxysilane) is followed by29Si NMR and rheological measurements. The structural evolution of the material from the starting sol to the thermally treated gel is studied using low angle X-ray diffraction. The textural characteristics of the gels are correlated with the nature of the surfactant molecules.
14 citations
01 Jan 1994
TL;DR: In this article, a quasi-long-range positional solid-like order along the direction perpendicular to the layers is described, where the surfactant density is modulated along the z-direction with a well-defined period.
Abstract: As previous chapters have described, surfactants in solution lead to a large number of fascinating structures, among which are the lyotropic liquid crystal phases [1] Liquid crystals exhibit long range order: orientational (nematics, see Chap 3) and positional (lamellar, hexagonal or cubic—see Secs 143–4 and Chap 4) The lamellar phases consist of stacks of surfactant bilayers separated by solvent, usually water In this chapter we are concerned only with the lamellar L α phase Figure 61 shows a schematic representation of such a structure There is quasi-long-range positional solid-like order along the direction perpendicular to the layers (which we label as the z-direction): the surfactant density is modulated along the z-direction with a well-defined period, the repeat distance d In the two other, in-plane, directions (x and y) the system is liquid-like and the solvent and surfactant molecules are free to move in this plane In general, at lower temperatures the L α phase may undergo a phase transition to the lamellar L β1 ,phases where the surfactant molecules exhibit various degrees of in-plane positional and orientational order [2] The lamellar L α phase has the symmetry of the smectic A phase encountered in thermotropic liquid crystals [3]; there are nevertheless important reasons for specifically studying such lyotropic smectics First, their most striking property is that the repeat distance d can be varied continuously, upon addition of an appropriate solvent
TL;DR: In this paper, the equilibrium fluctuations and weakly out-of-equilibrium relaxation properties of doped solvent dilute lamellar phases are investigated, both theoretically and experimentally, in the low-frequency, longwavelength limit.
Abstract: The equilibrium fluctuations and weakly out-of-equilibrium relaxation properties of “doped solvent" dilute lamellar phases are investigated, both theoretically and experimentally, in the low-frequency, long-wavelength limit. The physical system of interest is a three-component smectic A lyotropic liquid crystal where surfactant bilayers infinite in extent are periodically stacked along one direction in space and separated by a colloidal solution. Two experimentally relevant modes are found in the lowest frequency part of the fluctuation spectrum of such multicomponent systems. Both are associated to the relaxation of coupled layer displacement and colloid concentration waves. In the limit of small coupling, one mode is close to the well-known undulation/baroclinic mode of two-component lamellar phases, while the other corresponds to the Brownian diffusive motion of the colloid in an anisotropic medium. Elastic constants of the smectic liquid crystal and diffusion parameters of the colloidal solution may be deduced from a measurement of the anisotropic dispersion relation of these two modes, as illustrated by dynamic light scattering experiments on the ferrosmectic system.
Journal Article•
TL;DR: Congo Red immobilized to heat-aggregated immunoglobulins and antibodies in the immune complex was found to retain its binding ability, confirming its possible usefulness for drug transport.
Abstract: Lyotropic liquid crystal mesophases, represented in this work by Congo Red bis azo dye solution, were proposed as systems to carry drugs to immuno-selected targets. The possible use of Congo Red for this aim arises from its liquid crystalline features, enabling it to attach to immune complexes as polymolecular, ordered conglomerates and simultaneously to incorporate many organic compounds into its mesophase, largely independent of the water with a specific but adaptive molecular organization. Molecules with planar rigid structure, and/or large hydrophobic fragments, especially those with a positively charged group in the molecule, are found to be incorporated best. Rhodamine B, Rhodamine 6G and adriamycine, which have the assumed binding features, were tested as model compounds and were found to be readily engaged into Congo Red mesophase. The effect of hydrophobicity on ligand binding was evaluated following the incorporation of homologic 10, 12, 14, 16 carbon chain organic acids and the effect of charge using small mobile tandem molecules of pI differing by a few pH units (lysine-norleucine, tyrosine-tyramine). Positive charge seems to affect binding especially by influencing the organization of molecules and the shape of the micelle simultaneously. Congo Red immobilized to heat-aggregated immunoglobulins and antibodies in the immune complex was found to retain its binding ability, confirming its possible usefulness for drug transport.
TL;DR: In this paper, the authors measured self-diffusion coefficients of amphiphile and water molecules in novel inverse micellar lyotropic cubic phases using the pulsed field gradient NMR technique.
Abstract: We have measured self-diffusion coefficients of amphiphile and water molecules in novel inverse micellar lyotropic cubic phases using the pulsed field gradient NMR technique. We investigated two different ternary lyotropic systems: oleic acid/sodium oleate/water, and dioleoylglycerol/dioleoylphosphatidylcholine/water. Both of these systems have previously been shown by one of us to form a cubic phase of space group Fd3m, whose structure is a complex packing of two types of disconnected quasi-spherical inverse micelles embedded in a 3D hydrocarbon matrix. The amphiphile translational diffusion coefficients determined for the first time by 1H NMR in both systems are surprisingly large. Thus the self diffusion coefficients of amphiphiles may not provide a reliable way of distinguising inverse micellar from inverse bicontinuous phases. The water self-diffusion coefficient has been determined to have a value of 2·4 × 10−12 m2 s−1, a value which is more than two orders of magnitude lower than that typi...
TL;DR: In this paper, the rheological behavior of AOT/water liquid crystalline phases containing NaCl or decane is examined, and strong effects are noted on the elastic and loss moduli as well as on the complex and dynamic viscosities.
TL;DR: In this article, it was revealed that a concentrated chloroform solution of poly(2,5-dinonyloxy-p-phenylenevinylene) (NO-PPV) can be in a lyotropic liquid crystalline state at room temperature.
Abstract: It has been revealed that a concentrated chloroform solution of poly(2,5-dinonyloxy- p-phenylenevinylene) (NO-PPV) can be in a lyotropic liquid crystalline state at room temperature. The lyotropic NO-PPV solution exhibits redshift of optical absorption compared with the isotropic solution. X-ray diffraction analysis of an NO-PPV film cast from the chloroform solution suggested that a so-called sanidic (boardlike) mesophase formed in the solution state: i.e. the polymer main chains are extended, aligned side-by-side, and stacked parallel to each other. Preparation of fibers and films with preferred orientation from the NO-PPV solution was also described.
TL;DR: In this article, the results of the selective association of a single-chain amphiphile in two series of binary mixtures organized in a flat monolayer are presented, which explains the existence of structural inhomogeneities in supramolecular aggregates of lipid molecules.
01 Jan 1994
TL;DR: In this article, the authors defined microemulsion as a thermodynamically stable, fluid, oil-water-surfactant mixture with intermediate-range correlations, and they differentiated microemulsions from ordinary three-component solutions.
Abstract: Mixtures of amphiphiles, water and oil can have structures [1, 2, 3] that have only microscopic correlations between the components (e.g., a three component solution) as well as long-range ordered structures (e.g., lyotropic liquid crystals). The term microemulsion, in its most general use, connotes a thermodynamically stable, fluid, oil-water-surfactant mixture. In practice, microemulsions are taken to consist of structures with intermediate-range correlations. The oil and water regions are fairly well separated and the surfactant molecules are organized as monolayers at the internal water-oil interfaces[4]. There are long-range correlations between the oil and water molecules which are segregated into domains of the order of hundreds of Angstroms. In addition, there are long range correlations among the surfactant molecules which self-assemble into a monolayer film at the set of internal water-oil interfaces. In this respect, microemulsions are differentiated from ordinary three-component solutions. However, the set of interfaces which comprise the microemulsion do not show long range order comparable to that found in lyotropic liquid crystals.
TL;DR: In this article, a mathematical expression for the echo attenuation in a PFG-SE experiment is derived, which is formally compact and easy to handle by computer simulations technique, and its application to hexagonal mesophases is discussed as an example of how to handle complex situations.
Abstract: The NMR Pulsed Field Gradient Spin-Echo method (PFG-SE) may be conveniently applied to the study of water self-diffusion in lyotropic liquid crystals, giving insight on their molecular organization. The technique has been widely used and mathematical descriptions of the experiments have been worked out which, although simple to visualize, may involve computer calculations rather cumbersome and time consuming. Here we derive a mathematical expression giving the echo attenuation in a PFG-SE experiment which is formally compact and easy to handle by computer simulations technique. Its application to hexagonal mesophases is discussed as an example of how to handle complex situations.
TL;DR: In this article, the Flory phase diagram for solutions of rod-like polymers reveals two possibilities for the formation of liquid crystal states, one involves high concentrations of polymer in good solvents and the other dilute solutions in poor ones.
01 Jan 1994
TL;DR: In this article, the stability of phases of thermotropic and lyotropic liquid crystals is discussed. And the ESR theory derived from ESR studies of molecular dynamics provides a basis for understanding the stability properties of these phases.
Abstract: Molecular theories, derived from ESR studies of molecular dynamics, that provide a basis for understanding the stability of phases of thermotropic and lyotropic liquid crystals, are discussed.
01 Jan 1994
TL;DR: In this article, the properties and peculiarities of amphiphilic molecules are presented together with some principles of thermodynamics of aggregation in aqueous solution (hydrophobic effect).
Abstract: Properties and peculiarities of amphiphilic molecules are presented together with some principles of thermodynamics of aggregation in aqueous solution (hydrophobic effect). We focus our attention on aggregates which are formed by amphiphiles in the presence of water. We consider the infinite aggregates showing long range translational order and having the classical lamellar, hexagonal and cubic structures. We focus our attention successively on the nematic lyotropic systems exhibiting orientational but not long range translational order. The available techniques (X-ray, NMR, ESR, fluorescence…) useful for studying lyotropic liquid crystals are presented briefly with the results obtained and the models used for investigating the symmetry, form and size of the aggregates and the orientational order of the constituent molecules.
TL;DR: In this article, the slow polarized fluctuations, previously identified as being of micellar origin, for a lyotropic system consisting of K-laurate, decanol, D2O, and presenting only the uniaxial calamitic nematic (Nc) phase (from among the three known nematic types: uniaaxial disk-like (ND), calamitic (nc), and biaxonial (NB) phases).
Abstract: Using a Rayleigh scattering light beating technique, we have made new measurements on the slow polarized fluctuations, previously identified as being of micellar origin, for a lyotropic system consisting of K-laurate, decanol, D2O and presenting only the uniaxial calamitic nematic (Nc) phase (from among the three known nematic types: uniaxial disk-like (ND), calamitic (Nc) and biaxial (NB) phases). An elaborated analysis of these data is made in order to clarify the relationship between the light scattering signals coming from the micellar fluctuations and those from (classical) orientational fluctuations. The main conclusions of this analysis are that the micellar mode is independent of the temperature and wave-vector, and that its relaxation frequency is substantially lower than that found previously for the same lyotropic components, but presenting the biaxial nematic phase. Finally, some considerations are made of the possible relationships between the micellar fluctuations and the structural...
01 Jan 1994
01 Jan 1994
TL;DR: In this article, an overview of the formation and structure of lyotropic liquid crystals is given, in particular considering the influence of molecular shapes and packing constraints on the phase equilibria.
Abstract: An overview of the formation and structure of lyotropic liquid crystals is given, in particular considering the influence of molecular shapes and packing constraints on the phase equilibria. Investigations of phase equilibria in phospholipid/hydrocarbon/water systems are found to be in good agreement with theoretical predictions. Aggregate structure, lipid head group hydration and counterion binding, have been studied by using nuclear magnetic resonance (NMR), electron spin resonance (ESR) and fluorescence light spectroscopy. The discussion is focused mainly on non-lamellar and cubic phases. NMR measurements of diffusion, spin relaxation and lineshape analysis can give detailed information about the structure and dynamics of cubic phases, information which is difficult to obtain by X-ray diffraction. ESR studies of micellar aggregates and vesicles are described. The ESR lineshape for some systems gives information about the size and shape of micellar aggregates. Time-resolved fluorescence spectroscopy is used to determine the aggregation number of micelles. The order and dynamics of fluorescence probes through the measurements of the fluorescence anisotropy decay are described. Finally, a discussion of electronic energy transfer in lamellar phases and lipid vesicles is given.
TL;DR: In this paper, a ternary system (lecithin - D2O - PAE16) was investigated using small angle X-ray diffraction and NMR.
Abstract: The subject of the present investigations is a ternary system (lecithin - D2O - PAE16). The methods of the small angle X-ray diffraction and NMR were used. In the region of the water swilling lamellar structure an intermediate phase as well as a room temperature hexagonal phase at low water concentrations were observed.
TL;DR: In this article, the diffusion constants of a microbial epoxidation reaction were determined by a special diffusion cell, and the diffusion rate strongly depended on the water content of the liquid crystals and the hydrophobicity of the reactant.
Abstract: Lyotropic liquid crystals are appropriate matrices for the immobilization of biocatalysts used for biocatalysis in organic solvents. For the reactants of an microbial epoxidation reaction, oxygen, propene, and propene oxide, the diffusion constants in lyotropic mesophases were determined by a special diffusion cell. The diffusion rate strongly depends on the water content of the liquid crystals and the hydrophobicity of the reactant.
TL;DR: In this article, a phase diagram for CHCl3-solutions of N-Octanoyl tetramers, hexamers, and octamers was presented, where the phase diagram consists of three regions (I, II, and III).
Abstract: N-Octanoyl-L-glutamic acid oligomer benzyl esters (residue number,N=1–4, 6, 8, and 12) have been synthesized. For the solid samples ofN=3–12, x-ray powder diffraction pattern and vibrational spectroscopic measurements have led to the assumption of a β-sheet structure. For the CHCl3-solutions of theN-octanoyl tetramers, hexamers, and octamers, the phase diagram consists of three regions (I, II, and III). Region I is an isotropic phase, in which the aggregate structure strongly depends upon concentration, and region II is a lyotropic liquid crystal area. Region III is a two-phase area in which regions I and II coexist. In the case of the trimer solutions, it consists of two regions (I and II). For the oligomers withN=3–12 in region I, it was assumed that micellization induces preferential stabilization of the β-sheet structure depending on the concentration. Further stabilization of the β-sheet structure, was found to occur in region II. For the hexamer, octamer, and dodecamer in CHCl3, results from light-scattering measurements have led to an estimate of the apparent weight-average molecular weights and aggregation numbers of the micelle in region I.