Polymers in lyotropic liquid crystals

Polymers can be incorporated into lamellar liquid crystalline systems without the phenomena of macroscopic phase separation occurring. By playing with the inter-membrane interactions and the polymer–bilayer interactions the properties of the lamellar system can be modified significantly. This is not only of interest as a fundamental prerequisite to life, but it also opens new fields of application.     

Order parameters of dye molecules in lyotropic nematic mesophases

The alignment in a magnetic field of two similar azo dyes in binary nematic lyotropic phases (C₇F₁₅CO₂NH₄ and C₈F₁₇CO₂NH₄ in D₂O) has been studied. The order 5 parameter for the dyes was determined by measuring quadrupolar splittings (deuterium N.M.R.), the anisotropy of the electric conductivity and dichroism. The order parameter of the dye fixed in the disc-like perfluoro micelle with positive diamagnetic anisotropy was determined as a function of magnetic field strength, surfactant concentration, temperature and chain length. In addition the time constants for orientation and disorientation were determined.     

Nematic-isotropic phase transition in lyotropic liquid crystals

We propose a Landau-de Gennes phenomenological model to describe the nematic-isotropic phase transition in lyotropic liquid crystals. The possibility of a first or second order transition is explored by means of the variation of the concentration of surfactant. We show that a Landau point on the nematic-isotropic phase transition line can be achieved under certain conditions. The theoretical predictions are found to be in good qualitative agreement with available experimental results.     

Nematic-isotropic phase transition in lyotropic liquid crystals

We propose a Landau-de Gennes phenomenological model to describe the nematic-isotropic phase transition in lyotropic liquid crystals. The possibility of a first or second order transition is explored by means of the variation of the concentration of surfactant. We show that a Landau point on the nematic-isotropic phase transition line can be achieved under certain conditions. The theoretical predictions are found to be in good qualitative agreement with available experimental results.     

Polysaccharide-induced order-to-order transitions in lyotropic liquid crystals

We report on the order-to-order transitions of lyotropic liquid crystals formed by self-assembled monogylcerides and water in the presence of polysaccharides of various molecular weights. The phase diagram of monoglyceride-water-polysaccharide systems, their morphology, and the topology of liquid crystalline structures were determined by combining optical cross-polarization, oscillatory shear rheometry, and small-angle X-ray scattering. The presence of hydrophilic mono-, oligo-, and polysaccharides in the water domains of liquid crystalline phases resulted in a general decrease of the cubic-to-hexagonal transition temperature. Provided that the sugar could fit within the water channels, the decrease was observed to be dependent on the polysaccharide concentration but independent of its molecular weight. For isotropic bicontinuous cubic phases, monomeric sugars such as glucose were reported to shrink the lattice parameter of the structure without inducing phase transitions. However, when a polymeric form of glucose was used, such as dextran, transitions from the gyroidal Ia3d cubic phase to double diamond Pn3m cubic phases were observed at well-defined molecular weights of polysaccharide. These results were interpreted in terms of size exclusions of polymer sugars by the water domains of the liquid crystal phases as well as the different topologies of water channels. Molecular dynamics simulations of polysaccharides in the water environment were performed to support these findings.     

pH-responsive lyotropic liquid crystals for controlled drug delivery

We present a food-grade lyotropic liquid crystal system, capable of responding to pH variations with a reversible switch in both the structure and physical properties. The system, which is composed by monolinolein and linoleic acid (97:3 wt % ratio) in the presence of excess water at 37 °C and 150 mM ionic strength, is specifically designed to reversibly change from a Im3m reverse bicontinuous cubic phase to a H(II) reverse columnar hexagonal phase, when changing the pH from neutral (pH 7) to acidic (pH 2) conditions, to simulate intestine and stomach conditions, respectively. The pH responsiveness is provided by the linoleic acid, which, being a weak acid (pK(a) ≈ 5), is essentially in the deprotonated charged state at pH 7 and mainly protonated and neutral at pH 2, imposing changes in the critical packing parameter (CPP) of the lyotropic liquid crystal. The use of this system as an efficient controlled-release delivery vehicle is demonstrated on the model hydrophilic drug phloroglucinol, by both release and diffusion studies at different pH, as followed by ultraviolet-visible (UV-vis) spectroscopy. The Im3m cubic phase at pH 7 is shown to release 4 times faster than the H(II) phase at pH 2, making this system an ideal candidate for oral administration of drugs for targeted delivery in intestine or colon tracts.     

Inertial effects in rotating lyotropic liquid crystals

The orientation of the director of a lyotropic liquid crystal with negative anisotropy of the diamagnetic susceptibility is studied when the sample is spun at various speeds and angles from the magnetic field. Different behaviours is observed at low and high spinning speeds where the orientation is governed by the magnetic and the inertial torques, respectively. At intermediate frequencies it is possible to reach an equilibrium between these two torques. The evolution of this equilibrium with the average magnetic torque allows one to form a conclusion on the inertial nature of this effect.     

Inertial effects in rotating lyotropic liquid crystals

Abstract

The orientation of the director of a lyotropic liquid crystal with negative anisotropy of the diamagnetic susceptibility is studied when the sample is spun at various speeds and angles from the magnetic field. Different behaviours is observed at low and high spinning speeds where the orientation is governed by the magnetic and the inertial torques, respectively. At intermediate frequencies it is possible to reach an equilibrium between these two torques. The evolution of this equilibrium with the average magnetic torque allows one to form a conclusion on the inertial nature of this effect.     

Particle tracking microrheology of lyotropic liquid crystals

We present comprehensive results on the microrheological study of lyotropic liquid crystalline phases of various space groups constituted by water-monoglyceride (Dimodan) mixtures. In order to explore the viscoelastic properties of these systems, we use particle tracking of probe colloidal particles suitably dispersed in the liquid crystals and monitored by diffusing wave spectroscopy. The identification of the various liquid crystalline phases was separately carried out by small-angle X-ray scattering. The restricted motion of the particles was monitored and identified by the decay time of intensity autocorrelation function and the corresponding time-dependent mean square displacement (MSD), which revealed space group-dependent behavior. The characteristic time extracted by the intersection of the slopes of the MSD at short and long time scales, provided a characteristic time which could be directly compared with the relaxation time obtained by microrheology. Further direct comparison of microrheology and bulk rheology measurements was gained via the Laplace transform of the generalized time-dependent MSD, yielding the microrheology storage and loss moduli, G'(ω) and G'(ω), in the frequency domain ω. The general picture emerging from the microrheology data is that all liquid crystals exhibit viscoelastic properties in line with results from bulk rheology and the transition regime (elastic to viscous) differs according to the specific liquid crystal considered. In the case of the lamellar phase, a plastic fluid is measured by bulk rheology, while microrheology indicates viscoelastic behavior. Although we generally find good qualitative agreement between the two techniques, all liquid crystalline systems are found to relax faster when studied with microrheology. The most plausible explanation for this difference is due to the different length scales probed by the two techniques: that is, microscopical relaxation on these structured fluids, is likely to occur at shorter time scales which are more suitably probed by microrheology, whereas bulk, macroscopic relaxations occurring at longer time scales can only be probed by bulk rheology.     

Ion transport in polymerized lyotropic liquid crystals containing ionic liquid

In this work, we investigate the effect of morphology and segmental dynamics on ion transport in polymerized lyotropic liquid crystals (polyLLCs) containing 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). We demonstrate that two important factors, which affect ion conduction in polyLLCs, are grain size and chain density at the interface. The polyLLC with large grain size (70 nm) shows significant reduction in ion conductivity (one order of magnitude) compared to its homopolymer/IL mixture. However, the polyLLC with small grain size (20 nm) has little difference in ion conductivity compared to its homopolymer/IL mixture. It is observed that decreasing the chain density enhances the interaction of IL with polymer chains and consequently slows the relaxation of polymer chains. In addition, comparing the dynamics of polymer chains in mixtures of homopolymer/IL and templated LLC mesophases shows that the confinement in LLC structure prolongs the relaxation of polymer chains.     

Thermoanalytical investigation of lyotropic liquid crystals and microemulsions for pharmaceutical use

The interactions between surfactant and water were studied thermoanalytically focusing on the lyotropic liquid crystalline and microemulsion region in four ternary systems containing Cremophor EL and Cremophor RH40 as surfactants, neutral oil and isopropyl myristate as oily components. Subzero temperature DSC (SZT-DSC) measurements were carried out to determine the quantity of the bound water forming a hydration layer in surfactant microstructures, and the amount of free water, which has physico-chemical properties not much different from those of pure water. The variation of the surfactant:bound water ratio in the function of water concentration was also investigated. Phase changes detected by the SZT-DSC measurements were confirmed by polarization-microscopic and rheological investigations.     

Textures and defects in lyotropic liquid crystals of ethyl-cyanoethyl cellulose

Textures and defects in ethyl-cyanoethyl cellulose [(E-CE)C]/dichloroacetic acid (DCA) cholesteric liquid crystalline solutions and in (E-CE)C/polyacrylic acid (PAA) composites were observed and studied by polarizing microscopy and electron microscopy. The existence of χ, λ and τ disclinations were observed in the mesophase with disk-like and band-like textures. Pairs of disclinations with different signs were also found in the mesophase with the band-like texture. Domain walls were observed in (E-CE)C/PAA composite films with cholesteric order by TEM. The orientation of polymer chains in the vicinity of the core of the disclinations is discussed.     

Rheological properties of lyotropic liquid crystals encapsulating curcumin

This study constructed new curcumin-loaded lyotropic liquid crystals containing pharmaceutically accepted oil, and ethyl oleate (EtOL). Three liquid crystalline phases including lamellar, hexagonal, and cubic phases were identified by means of the polarized optical microscopy and rheology method. By analyzing the shear viscosity (η_0.1), the viscosity of curcumin-liquid crystals is smaller than those without curcumin. Dynamic rheological results show that: Dissolved curcumin in EtOL can make the elastic modulus of hexagonal and cubic phase increase compared with that without curcumin, while the elastic modulus of lamellar phase decreases. Dissolved curcumin in Brij 97 can lead to the decreasing of the elastic modulus for cubic and lamellar phases, whereas it has little influence on hexagonal phase. When the curcumin is solubilized in both EtOL and Brij 97, the elastic modus of hexagonal phase increase, the elastic modus of lamellar and cubic phases decrease compared with that without curcumin. Furthermore, three temperature turning points were identified by the change in the slope of tanδ (G″/G′) for curcumin-hexagonal liquid crystal. These studies might be a help to study the storage of drug carrier and in vitro release properties of lyotropic liquid crystals containing curcumin.     

First-order transition between nematic phases in lyotropic liquid crystals

Experimental evidence for the existence of a first order transition between N_c-N_d 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.     

Flow activation free energy in cholesteric lyotropic liquid crystals

The flow activation free energy ( ΔG *) is the minimum energy necessary to induce a flow in a system that is at rest. It can be calculated from the system viscosity using the Andrade--Eyring theory. In the present work the flow activation free energy of cholesteric lyotropic liquid crystals was studied as a function of D-(+)-mannose concentration added to a nematic mesophase. The results obtained showed that all the systems can be characterized as Newtonian, but a smooth time-dependent effect can be observed mainly in systems with a lower chiral inductor concentration. It has also been observed that an increase of cholestericity leads to a decrease of ΔH * values until a limit is reached at 1 mol % of inductor. From a positive ΔS * variation it was possible to verify the existence of a locally less organized transient state during the process of micellar diffusion. When the cholesterization process was considered, the increase of the inductor concentration leads to a decrease of ΔS * and consequently to a system, as a whole, more orderly, possibly as a result of the restriction of movement caused by the presence of chiral interactions.     

Thermally induced cholesteric-isotropic transition in lyotropic polypeptide liquid crystals

The thermally induced cholesteric to isotropic transition of lyotropic polybenzylglutamate liquid crystals in six solvent combinations was examined optically. The solvents chosen for study support both low and high pitch values, positive and negative pitch temperature coefficients, and polypeptide denaturation. The biphasic zone below the clearing temperature is broad and solvent dependent. Unusual large-scale phase separations and solution morphologies occur in some solvents. No evidence was found for pretransitional chiral orientational ordering near the clearing point in the high-temperature isotropic phase.     

Micellar shape dependence of cholesteric pitch in lyotropic liquid crystals

A generalized Landau-Ginzburg-de Gennes theory of cholesteric pitch in lyotropic chiral liquid crystals is presented. Using the non-critical order parameter, introduced by Toledano and Figueiredo Neto, the question of pitch dependence on micellar shape is addressed. This extra order parameter accounts for the shape change of the micelles. The predictions agree qualitatively with the unique experimental observations of Lopes and Figueiredo Neto.     

溶致液晶的结构及应用研究进展

本文评述了溶致液晶的相态和结构以及其相态随浓度变化的特点，并着重介绍了溶致液晶在新型纳米材料全盛中的应用，在生物医学中的应用，在化学反应中的催化作用，以及在工业中的作用。     

Conformational peculiarities of alcohols incorporated in lyotropic and thermotropic liquid crystals

Conformational characteristics of 1-butanol incorporated not only in hexagonal and lamellar aggregates formed by a lyotropic liquid crystal composed of sodium octanoate, 1-butanol, and water but also in a thermotropic liquid crystal, 4'-methoxybenzylidene-4-n-butylaniline (MBBA), have been investigated from 2H NMR quadrupolar splittings of the perdeuterated and partially deuterated compounds. In the lyotropic phases, 1-butanol shows strong trans preferences and renders itself extended, and octanoate decreases the trans fraction toward the methyl terminal to fill the inner space of the aggregate on behalf of 1-butanol. In MBBA, 1-butanol prefers globular conformations. This tendency was also indicated from the phase behaviors of 1-butanol/MBBA and 1-decanol/MBBA systems. In the nematic field, two successive C-C bonds of 1-butanol mostly adopt g+/-g+/- conformations, which are formed in the vicinity of the headgroup of 1-decanol in the lamella of the sodium octanoate/1-decanol/water system. A large degree ofconformational freedom near the hydroxyl group of alcohols, being shown by ab initio molecular orbital calculations at the Gaussian-2 level, permits them to change conformation for each environment.