Lyotropic Systems Research Articles

Impact of Topology on the Characteristics of Water inside Cubic Lyotropic Liquid Crystalline Systems.

Water molecules present inside the lipid-based cubic liquid crystalline phases are found to play a major role in wide range of applications, such as protein crystallization, virus detection, delivery of drug and biomolecules, etc. In this regard, it is crucial to elucidate static and dynamic properties of the water molecules in the nanochannels and to explore the effect of geometrical topology on the nature of the water inside the different cubic phases. In the present work, we have incorporated two probes, coumarin-343 (C-343) and coumarin-480 (C-480), in two cubic phases with different symmetries, namely gyroid ( Ia3 d) and double diamond ( Pn3 m) with the same water content (22%), to probe the micropolarity, the microviscosity, and the hydration dynamics at different hydrophobic depths in the mesophases. Steady state results estimate the polarity at the lipid-water interface to be similar to that of ethanol, and the polarity near the more hydrophilic parts of the nanochannel resembles that of ethylene glycol. We have also observed a gradient in the microviscosity inside the LLC nanochannels from time-resolved fluorescence anisotropy studies. The hydration dynamics, which play a key role in the numerous applications of the mesophases, have been probed by the time-dependent Stokes shift method of the two probes, revealing the existence of three kinds of dynamics. The difference in the hydration dynamics inside the two mesophases, where the water molecules confined in the Ia3 d phase exhibit a slower dynamics compared to that in Pn3 m, is the prime importance of this work. The underlying reason for this disparity is majorly associated with the differences in the topology of the two structures including the hydrophobic packing stress, the negative interfacial curvature, and the curvature elastic energy of the lipid-water interface. We believe that this kind of correlation between the structural topology of the different cubic LLC mesophases and nature of the water nanochannel will help to boost the applications of the cubic phases in the future.

Preparation and chiroptical properties of cellulose chlorophenylcarbamate–silica hybrids having a chiral nematic mesomorphic structure

An attempt was made to fabricate optically functional cellulosic–silica hybrid materials wherein a helically ordered mesomorphic structure of the cellulosic component was fixed. Cellulose 3-chlorophenylcarbamate (3Cl-CPC) and cellulose 4-chlorophenylcarbamate (4Cl-CPC) were synthesized by carbanilating reaction of cellulose with 3-chlorophenyl or 4-chlorophenyl isocyanate in a homogeneous solution system. The hydrophobic cellulose derivatives were examined for the solubility and liquid crystallinity in various solvents containing alkoxysilane as a main component. Concentrated (∼40 wt%) solutions of 3Cl-CPC in 3-aminopropyltrimethoxysilane (APTMS) and those of 4Cl-CPC in a mixed solvent of tetramethoxysilane (TMOS)/N,N-dimethylformamide (DMF)/dichloroacetic acid (DCA) formed a chiral nematic mesophase to impart vivid reflection colors. These liquid crystalline solutions were subjected to a sol–gel conversion process of the respective alkoxysilane components in moist air. In the process for the 4Cl-CPC lyotropic system, we utilized a "surface-coating solvent" consisting of TMOS/phenyltrimethoxysilane/DCA to facilitate the sol–gel reaction of TMOS and also to preserve the reflective coloration. Thereby a left-handed chiral nematic hybrid series of 4Cl-CPC–silica was successfully obtained as a monolithic glassy bulk showing iridescent colors. The 3Cl-CPC/APTMS lyotropics were readily converted into a colored solid form without any coating solution, resulting in production of a right-handed chiral nematic series of 3Cl-CPC–silica. Besides investigating the chiroptical characteristics of the liquid crystalline solutions and hybrids, we preliminarily tried separating a racemic compound into two enantiomers by open column chromatography using the cellulosic–silica hybrids as a filler material of the column.

Visible light-triggered cargo release from donor acceptor Stenhouse adduct (DASA)-doped lyotropic liquid crystalline nanoparticles

Light-responsive nanocarriers are applicable as non-invasive, highly tunable and precisely controlled drug delivery systems. Here, we report a new nanocarrier system, achieved by doping D1, a type of green light–responsive donor acceptor Stenhouse adduct (DASA), into a lipid-based lyotropic liquid crystalline system. Time-resolved small angle X-ray scattering was used to confirm that the matrix underwent a rapid and fully reversible phase transition from lamellar to inverse cubic phase upon irradiation with green light (532 nm), reverting back on removal of light. Fluorescein isothiocyanate–dextran (FD4) was used as a model hydrophilic cargo. The release of cargo upon varying irradiation parameters was investigated in vitro which showed that irradiation can trigger a burst release of FD4 upon phase transition. This additive shows promise for the development of new visible light-activated, “on demand” drug delivery systems.

Liquid Crystalline Tactoidal Microphases in Ferrofluids: Spatial Positioning and Orientation by Magnetic Field Gradients

Summary Macroscopic manipulation of self-assembly in lyotropic systems, such as chiral nematic liquid crystals formed by cellulose nanocrystals, is kinetically hindered by the similarity between isotropic and anisotropic phases in composition and physical properties. By creating a significant difference in volumetric magnetic susceptibility between discrete liquid crystalline tactoids and continuous isotropic phases (based on the exclusion effects of tactoids on superparamagnetic doping nanoparticles), we achieved position and orientation control of liquid crystalline tactoids by magnetic field gradients as weak as several hundred gauss per centimeter, where the movement of tactoids is determined by competition between magnetic and gravitational acceleration fields. We also undertook a preliminary examination of the trapping of a liquid crystalline phase in the potential well of a quadrupole magnetic field. This method enabled us to control the phase separation rate and configuration, as well as the orientation of director fields in both tactoids and macroscopic ordered phases.

Re-entrant direct hexagonal phases in a lyotropic system of surfactant induced by an ionic liquid

ABSTRACTIn the present study, an ionic liquid (IL), known as green solvent, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) with four carbons in the hydrophobic chain (C-4) has been used as an additive to modify the self-assembled aggregates of an anionic surfactant sodium dodecyl sulfate (SDS) and then the evolution of the liquid crystalline phases has been investigated. Small angle synchrotron x-ray diffraction study has revealed an unprecedented phase sequence where a hexagonal phase (HI) of direct cylindrical micelles is observed to evolve to another hexagonal phase (HII) of, again, direct cylindrical micelles with a lamellar phase () as the intermediate. The rheological data and the theoretical calculations have confirmed the phases. To understand such a phase behaviour of the system, the work is extended by considering the ionic liquids with the same head group but of shorter (C-2) and longer (C-10) hydrocarbon chains compared to BMIM-BF4. While the shorter chain IL causes the hexagonal phase to form rectangular (R) phase, the longer chain is observed to induce the lamellar phase (). The molecular mechanism of appearance of such different phases has been discussed.

Optical signal and optical axes in uniaxial and biaxial nematic phases

ABSTRACTIn this work we will study the behavior of the optical signal and optical axes along the continuous transition of a lyotropic system from a nematic discotic () phase to a nematic calamitic () phase; we will study in detail the case in which there is a biaxial nematic () phase at the interstice between these two uniaxial phases. It will be shown that the optical signal and optical axes change simultaneously in order to agree with the optical signals of the uniaxial phases at their borders: the optical signal is positive at the frontiers with the phase and it turns to be negative at the frontiers with the phase. Concomitantly, the optical axes rotates from the direction to the direction. We will illustrate these findings with experimental data that confirm our results.

Dark Conductivity and Photoconductivity of Nonaqueous Liposomes: a New Method for Measuring the Phase-Transition Temperatures of Lipid Membranes

A new method is developed to measure the phase-transition temperatures in artificial phospholipid membranes. This method is based on studying the temperature dependence of dark conductivity and photoconductivity in a symmetric cell with current-conducting indium–tin oxide (ITO) electrodes. Internal electron photoemission into a thin liposome layer is induced by visible and near IR light from the ITO electrodes. This method is applied to study the lyotropic phases in 1,2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) with ethylene glycol (EG) and glycerol (G). The results of time-of-flight measurements are used to calculate the carrier mobilities in liposome vesicles. The measurement results are compared with the results obtained by dc conductometry. We are the first to detect the effect of a positive temperature coefficient of resistivity in a liquid-crystal phase. The proposed method makes it possible to detect the phase transitions in lyotropic liquid-crystal systems and, hence, can be used to create biocompatible drug carriers based on thermosensitive liposomes.

Morphologic Properties, Texture Transformations and Optical Refracting Properties: Aqueous Bicomponent Amphiphilic Lyotropic Systems

AbstractThe mesomorphic, morphologic and optical refracting properties of the bicomponent amphiphilic lyotropic systems have been investigated. Five amphiphiles with various concentration combinations as cationic – cationic, anionic – anionic and cationic – anionic lyotropic mixtures have been used for preparation of lyotropic systems. The mixtures were prepared with a constant (amphiphile1 + amphiphile2)/water concentration ratio. Isotropic lyotropic phase and hexagonal and lamellar lyotropic mesophases have been found in lyotropic systems under investigations. Dynamics of change of the magneto-morphologic properties vs. time, character of the heterophase regions of the mesophase – isotropic liquid phase transitions and temperature dependencies of the optical refracting properties of these bicomponent amphiphilic lyotropic systems have been investigated.

Shape of Micelles and Temperature and Concentration Behavior of Optical Refractive Properties: Single Amphiphilic and Mixed Bicomponent Amphiphilic Lyotropic Systems

Lyotropic systems are bicomponent and/or multicomponent mixtures display physically isotropic and physically anisotropic properties and exhibit various types of isotropic lyotropic phases and anisotropic lyotropic mesophases. Structure units in lyotropic phases and mesophases are the nano-size three-dimensional nanoparticle supramolecular aggregates as the isometric and anisometric micelles. In this work, comparative investigations of the optical refractive properties of lyotropic micellar systems as mixtures of single amphiphile and mixed bicomponent amphiphiles in polar solvent have been carried out. Lauryltrimethyl ammonium bromide (LTAB) + water, cetyltrimethyl ammonium bromide (CTAB) + water, and (LTAB + CTAB mixture) + water lyotropic systems have been studied. Shapes of micelles in single component amphiphilic and bicomponent amphiphilic lyotropic systems have been estimated. Temperature and concentration dependences of the optical refractive index have been determined. Effect of the LTAB/CTAB concentration ratio on the refractive properties of mixtures under investigations has been found. Effect of length of the hydrophobic chain of amphiphile molecules with the same hydrophilic part on the refractive index of lyotropic systems is analysed.

Highly confined stacks of graphene oxide sheets in water.

Since the discovery of graphene oxide (GO), the most accessible of the precursors of graphene, this material has been widely studied for applications in science and technology. In this work, we describe a procedure to obtain GO dispersions in water at high concentrations, these highly dehydrated dispersions being in addition fully redispersible by dilution. With the availability of such concentrated samples, it was possible to investigate the structure of hydrated GO sheets in a previously unexplored range of concentrations, and to evidence a structural phase transition. Tentatively applying models designed for describing the small-angle scattering curve in the Smectic A (or [Formula: see text]) phase of lyotropic systems, it was possible to extract elastic parameters characterising the system on the dilute side of the transition, thereby evidencing the relevance of both electrostatic and steric (Helfrich) interactions in stabilising aqueous lamellar stacks of GO sheets.

Phase Boundaries, Optical Refraction and Specific Electrical Conductivity Properties in Lyotropic Micellar L1 Phase: Bicomponent Amphiphilic (DDTMABr + HDTMABr) + Water System

Abstract In this work, complex investigations of the temperature and concentration behaviour of the optical refraction properties and specific electrical conductivity properties in lyotropic micellar L1 phase have been carried out. Bicomponent amphiphilic (DDTMABr + HDTMABr) + water lyotropic systems with various DDTMABr/HDTMABr concentration ratios have been objects of our investigations. The phase diagram for L1 phase in this system has been determined. Effect of the DDTMABr/HDTMABr concentration ratios on the refractive index and specific electrical conductivity has been observed. The mutual influence of amphiphile with short alkyl chain (DDTMABr) and long alkyl chain (HDTMABr) on the phase states, refractive index and electrical conductivity properties has been found. Our results show that variation of the concentration ratio in a mixture of amphiphiles with different length of the non-polar tail gives possibility to regulate the hydrophilicity degree, optical density, refraction properties and specific electrical conductivity of mixed lyotropic systems.

Dry Thermotropic Glycolipid Self-Assembly:A Review

Also recognized as carbohydrate liquid crystals, glycolipids are amphiphiles whose basic unit comprises of a sugar group attached to an alkyl chain. Glycolipids are amphitropic, which means these materials form liquid crystal self-assemblies when dry (thermotropic) as well as when dissolved in solvents (lyotropic/surfactants) such as water. Many glycolipids are also naturally derived since these can be found in cell membranes. Their membrane and surfactant functions are largely understood through their lyotropic properties. While glycolipids are expected to play major roles as eco-friendly surfactants in the global surfactant market, their usefulness as thermotropic liquid crystal material is, to date, unknown, due to relatively lack of research performed and data reported in the literature. Understandably since glycolipids are hygroscopic with many hydroxy groups, removing the last trace water is very challenging. In recent time, with careful lyophilization and more consistent characterization technique, some researchers have attempted serious studies into "dry" or anhydrous glycolipids. Motivated by possible developments of novel thermotropic applications, some results from these studies also provide surprising new understanding to support conventional wisdom of the lyotropic systems. Here we review the dry state of glycosides, a family of glycolipids whose sugar headgroup is linked to the lipid chain via a glycosidic oxygen linker. The structure property relationship of both linear and anhydrous Guerbet glycosides will be examined. In particular, how the variation of sugar stereochemistry (e.g. anomer vs. epimer), the chain length and chain branching affect the formation of thermotropic liquid crystals phases, which not only located under equilibrium but also far from equilibrium conditions (glassy phase) are scrutinized. The dry glycolipid assembly has been subjected to electric and magnetic fields and the results show interesting behaviors including a possible transient current generation.

Molecularly Imprinted Microrods via Mesophase Polymerization.

The aim of the present research work was the synthesis of molecularly imprinted polymers (MIPs) with a rod-like geometry via “mesophase polymerization”. The ternary lyotropic system consisting of sodium dodecyl sulfate (SDS), water, and decanol was chosen to prepare a hexagonal mesophase to direct the morphology of the synthesized imprinted polymers using theophylline, methacrylic acid, and ethylene glycol dimethacrylate as a drug model template, a functional monomer, and a crosslinker, respectively. The obtained molecularly imprinted microrods (MIMs) were assessed by performing binding experiments and in vitro release studies, and the obtained results highlighted good selective recognition abilities and sustained release properties. In conclusion, the adopted synthetic strategy involving a lyotropic mesophase system allows for the preparation of effective MIPs characterized by a rod-like morphology.

Interplay of structure, elasticity, and dynamics in actin-based nematic materials

Achieving control and tunability of lyotropic materials has been a long-standing goal of liquid crystal research. Here we show that the elasticity of a liquid crystal system consisting of a dense suspension of semiflexible biopolymers can be manipulated over a relatively wide range of elastic moduli. Specifically, thin films of actin filaments are assembled at an oil-water interface. At sufficiently high concentrations, one observes the formation of a nematic phase riddled with [Formula: see text] topological defects, characteristic of a two-dimensional nematic system. As the average filament length increases, the defect morphology transitions from a U shape into a V shape, indicating the relative increase of the material's bend over splay modulus. Furthermore, through the sparse addition of rigid microtubule filaments, one can gain additional control over the liquid crystal's elasticity. We show how the material's bend constant can be raised linearly as a function of microtubule filament density, and present a simple means to extract absolute values of the elastic moduli from purely optical observations. Finally, we demonstrate that it is possible to predict not only the static structure of the material, including its topological defects, but also the evolution of the system into dynamically arrested states. Despite the nonequilibrium nature of the system, our continuum model, which couples structure and hydrodynamics, is able to capture the annihilation and movement of defects over long time scales. Thus, we have experimentally realized a lyotropic liquid crystal system that can be truly engineered, with tunable mechanical properties, and a theoretical framework to capture its structure, mechanics, and dynamics.

Effect of viscosity, pH and physicochemical parameters of solvent on the aggregation and dielectric behaviour of lyotropic liquid crystals binary mixtures

This paper reports on the synthesis of lyotropic liquid crystalline phases using cetyl pyridinium chloride and sodium dodecyl sulphate in the aqueous (water) and non-aqueous solvent (glycerol) of varying polarity and viscosities. Various crystal-like, liquid-like and liquid crystalline phases are seen in the different solvent media at the expense of increasing concentration of surfactants. It is interesting to highlight that highly viscous and little acidic (pH≈6) mixtures produce more ordered structures comparing to other. Aggregation of cetyl pyridinium chloride in both solvents is found thermally driven process as calorimetric transition confirmed the growth of the lyotropic phases at a higher temperature (331–345K) than 303K. Quenching has been evolved as the proficient technique to bring the higher temperature lyotropic liquid crystalline ordering to the room temperature without breaking the symmetry. Structural and polarizing optical microscopy measurement reveals that viscosity plays vital role on the aggregation in lyotropic liquid crystalline systems as glycerol based quenched and as-synthesized lyotropic liquid crystalline phases are found more ordered than other. Dielectric dynamics reveals that quenched cetyl pyridinium chloride/glycerol-based lyotropic liquid crystalline phases show higher dielectric constant; however, the reverse is true for the sodium dodecyl sulphate/glycerol lyotropic liquid crystalline phases. Dc conductivity of the order 10−5S/m is one of the significant finding of this study, which open up the application perspective of these phases.

Lyotropic Liquid-Crystalline Nanosystems as Drug Delivery Agents for 5-Fluorouracil: Structure and Cytotoxicity.

Lyotropic cubic liquid-crystalline systems have received increasing attention due to their unique microstructural and physicochemical properties as efficient nanocarriers for drug delivery. We report the preparation and characterization of bulk phases and cubosome dispersions of phytantriol loaded with the anticancer drug 5-fluorouracil, in neutral and anionic forms. In both cases, a Pn3m cubic phase was observed. The phytantriol phase behavior can be influenced by the addition of ionic agents, and, to this purpose, a positively charged lipid, such as N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride salt (DOTAP), was included in the studied formulations. It was found to induce a variation of the spontaneous membrane curvature of the phytantriol lipid bilayer, generating a transition from the Pn3m to the Im3m cubic phase. When 5-fluorouracil, in its anionic form (5-FUs), was encapsulated in these latter systems, a further transition to the HII hexagonal phase was observed as a consequence of the formation of a complex phytantriol/DOTAP/5-FUs. The physicochemical characterization was performed with various complementary techniques including synchrotron small-angle X-ray scattering, dynamic light scattering, and attenuated total reflection Fourier transform infrared and UV resonance Raman spectroscopies. Encapsulation of 5-fluorouracil in the corresponding nanodispersions was evaluated, and their in vitro cytotoxicity was assessed in MDA-MB-231 cell line. Phytantriol cubosomes containing 5-fluorouracil showed a higher toxicity compared with the bare drug solution, and hence they represent potential nanocarriers in the delivery of 5-fluorouracil for cancer therapy.

Structural and dielectric behaviors of Bi4Ti3O12 – lyotropic liquid crystalline nanocolloids

ABSTRACTWe investigated the structural and dielectric dynamics of nanocolloids comprising lyotropic liquid crystals and bismuth titanate (Bi4Ti3O12) spherical nanoparticles (≈16–18 nm) of varying concentration 0.05 and 0.1 wt%. The lyotropic liquid crystalline mixture was prepared by a binary mixture of cetylpyridinuium chloride and ethylene glycol mixed in 5:95 wt% ratio. Binary lyotropic mixture exhibited hexagonal lyotropic phase. Structural and textural characterizations of nanocolloids infer that the nanoparticles were homogeneously dispersed in the liquid crystalline matrix and did not perturb the hexagonal ordering of the lyotropic phase. The dielectric constant and dielectric strength were found to be increased with the rise in the Bi4Ti3O12 nanoparticles concertation in the lyotropic matrix. A significant increase of one order was observed in the ac conductivity of colloidal systems as compared to the non-doped lyotropic liquid crystal. Relaxation parameters of the non-doped lyotropic liquid crystal and colloidal systems were computed and correlated with other parameters.

Line Tension of Twist-Free Carbon Nanotube Lyotropic Liquid Crystal Microdroplets on Solid Surfaces.

Line tension, i.e., the force on a three-phase contact line, has been a subject of extensive research due to its impact on technological applications including nanolithography and nanofluidics. However, there is no consensus on the sign and magnitude of the line tension, mainly because it only affects the shape of small droplets, below the length scale dictated by the ratio of line tension to surface tension σ/τ. This ratio is related to the size of constitutive molecules in the system, which translates to a nanometer for conventional fluids. Here, we show that this ratio is orders of magnitude larger in lyotropic liquid crystal systems comprising micrometer-long colloidal particles. Such systems are known to form spindle-shaped elongated liquid crystal droplets in coexistence with the isotropic phase, with the droplets flattening when in contact with flat solid surfaces. We propose a method to characterize the line tension by fitting measured droplet shape to a macroscopic theoretical model that incorporates interfacial forces and elastic deformation of the nematic phase. By applying this method to hundreds of droplets of carbon nanotubes dissolved in chlorosulfonic acid, we find that σ/τ ∼ -0.84 ± 0.06 μm. This ratio is 2 orders of magnitude larger than what has been reported for conventional fluids, in agreement with theoretical scaling arguments.

Development and In Vitro Evaluation of Lyotropic Liquid Crystals for the Controlled Release of Dexamethasone.

In this study, amphiphilic polymers were investigated as biomaterials that can control dexamethasone (DXM) release. Such materials present interfacial properties in the presence of water and an oily phase that can result in lyotropic liquid crystalline systems (LLCS). In addition, they can form colloidal nanostructures similar to those in living organisms, such as bilayers and hexagonal and cubic phases, which can be exploited to solubilize lipophilic drugs to sustain their release and enhance bioavailability. It was possible to obtain lamellar and hexagonal phases when combining polyoxyethylene (20) cetyl ether (CETETH-20) polymer with oleic acid (OA), N-methylpyrrolidone (P), isopropyl myristate (IM), and water. The phases were characterized by polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), rheological, textural, and bioadhesion analyses followed by an in vitro release assay. All samples showed elastic behavior in the rheology studies and hexagonal samples containing P and IM showed the highest adhesiveness. The drug release profile of all LLCS presented an average lag time of 3 h and was best fitted to the Korsmeyer-Peppas and Weibull models, with controlled release governed by a combination of diffusion and erosion mechanisms. These systems are potential carriers for DXM and can be explored in several routes of administration, providing potential advantages over conventional pharmaceutical forms.

Revisiting (hydroxypropyl) cellulose (HPC)/water liquid crystalline system

ABSTRACTThe discovery of a cholesteric liquid crystalline phase in concentrated aqueous solutions of (hydroxypropyl)cellulose (HPC) dates back to the 1970s. Due to its biocompatibility, low cost and ease of conversion to fibres and films, HPC is still the target of numerous studies. In this article, some of the properties of the HPC/water lyotropic system are reviewed, and original results describing a humidity-generated instability on HPC fibres are presented. The use of HPC films which respond to external stimuli is highlighted. In particular, novel applications include the manufacture of soft motors driven by a difference of humidity, and the production of electro-optical cells when the solid films are used in conjunction with low molecular mass thermotropic mesogens.