Showing papers on "Lyotropic liquid crystal published in 1999"

Nanostructure templating in inorganic solids with organic lyotropic liquid crystals

Abstract: Various nanoscale semiconducting superlattices have been generated by direct templating in a lyotropic organic liquid crystal. These include superlattices of CdS, CdSe, and ZnS, templated in a liquid crystal formed by oligoethylene oxide oleyl ether amphiphiles and water. The semiconductor growth process copied the symmetry and characteristic dimensions of the original mesophase by avoiding growth of mineral within regularly spaced hydrophobic regions. The final product was a superlattice structure in which a mineral continuum was featured with hexagonally arranged cylindrical pores 2−3 nm in diameter and 5 nm apart. Most importantly, the superlattice morphology of the nanostructured systems in contact with the mesophase was found to be thermodynamically stable with respect to the solid lacking nanoscale features. We also found that both the morphology of features in the nanostructured solids and their dimension can be controlled through the amphiphile's molecular structure and water content in the liquid...

Heterogeneous Catalysis with Cross‐Linked Lyotropic Liquid Crystal Assemblies: Organic Analogues to Zeolites and Mesoporous Sieves

Abstract: Organic, nanoporous heterogeneous catalysts based on a carboxylate-containing, amphiphilic mesogen catalyze the Knoevenagel condensation (see schematic representation). These networks maintain their order in solution and can be recycled. Enhanced basicity, excellent site accessibility, and substrate size exclusion are features of these nanostructured systems.

Curvature walls and focal conic domains in a lyotropic lamellar phase

Abstract: In the quasi-ternary CPCl/brine/hexanol lyotropic system, the interface of the \({L_\alpha }\) lamellar and L3 sponge phases displays a phenomenon of epitaxy: the layers of the lamellar phase tend to make a constant non-trivial angle with the interface. Thin samples of lamellar phase embedded in the sponge phase are thus submitted to oblique anchoring conditions and defects are created in the lamellar phase in order to satisfy the bulk lamellar ordering and the boundary conditions. We have studied small droplets of lamellar phase in the sponge phase. They do not exhibit the classic \({L_\alpha }\) defects (focal conic domains) but wall defects, which appear in order to satisfy the smectic elasticity and the boundary conditions. Moreover we show through experiments in controlled geometry that, even in the presence of focal conic domains, wall defects control the size and periodicity of the textures which are observed at the interface.

Salted mesostructures: salt-liquid crystal templating of lithium triflate-oligo(ethylene oxide) surfactant-mesoporous silica nanocomposite films and monoliths

Abstract: A lyotropic lithium triflate-silicate liquid crystal is utilized as a supramolecular template for a ‘one-pot’ synthesis of a novel ionically conducting nanocomposite material, denoted meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 , in the form of a film or monolith. In this structure Li + ions interact, in a crown ether-like fashion, with oligo(ethylene oxide) head groups of a non-ionic surfactant assembly that is imbibed within the channels of hexagonal mesoporous silica. Details of the acid catalyzed polymerization of the silicate oligo(ethylene oxide) surfactant co-assembly in the presence of lithium triflate have been investigated using polarized optical microscopy (POM), powder X-ray diffraction (PXRD), multinuclear nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. Insight into the incorporation of Li + and CF 3 SO 3 – ions into meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 was obtained using NMR and Fourier transform (FT) Raman spectroscopy. Collectively the results indicate that lithium ions coordinate to oxygens of the oligo(ethylene oxide) head group, maintain the structural integrity of both the silicate liquid crystal and templated mesoporous silica, and are essentially completely dissociated with respect to the triflate counteranion. ac Impedance spectroscopy, which bodes well for their use in the fields of polymer electrolytes and battery technology for meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 have demonstrated high ionic conductivities at room temperature measurements. Salt-liquid crystal templating may offer a general approach for synthesizing diverse kinds of salted mesostructures including redox active transition metal complexes, which may be reductively-agglomerated to form metal cluster-based meso-SiO 2 -C 12 (EO) 10 OH-M n or sulfided with H 2 S to produce semiconductor cluster-based meso-SiO 2 -C 12 (EO) 10 OH-(MS) n nanocomposites.

Self-assembly of nanocomposite materials

Abstract: A method of making a nanocomposite self-assembly is provided where at least one hydrophilic compound, at least one hydrophobic compound, and at least one amphiphilic surfactant are mixed in an aqueous solvent with the solvent subsequently evaporated to form a self-assembled liquid crystalline mesophase material. Upon polymerization of the hydrophilic and hydrophobic compounds, a robust nanocomposite self-assembled material is formed. Importantly, in the reaction mixture, the amphiphilic surfactant has an initial concentration below the critical micelle concentration to allow formation of the liquid-phase micellar mesophase material. A variety of nanocomposite structures can be formed, depending upon the solvent evaporazation process, including layered mesophases, tubular mesophases, and a hierarchical composite coating composed of an isotropic worm-like micellar overlayer bonded to an oriented, nanolaminated underlayer.

Thermotropic and lyotropic properties of n-alkyl-β-D-glucopyranoside surfactants

Abstract: We have studied the thermotropic and lyotropic phase behaviour of different monoalkyl glycosides using polarizing microscopy, differential scanning calorimetry and rheology. The dependence of the liquid crystal transition temperature and mesophase formation on the chain length of the hydrophobic tail has been studied. The melting transition for each of the dry alkyl-glycosides corresponds to one or two solid–solid transitions, a solid–liquid crystalline transition and a liquid crystalline–liquid isotropic transition. The lyotropic behaviour follows the classical pattern established for the surfactants. In the system CXG1 (X=8, 10)–water, the mesophases observed with increasing the concentration are a hexagonal phase, a cubic phase and a lamellar phase. Caused by the strong kinetic hindrance, the cubic and hexagonal phases for the system C10G1(n-decyl-β-D-glucopyranoside)–water are only visible by polarization microscopy experiments. Rheological oscillation experiments permit detection of phase transition. In the low-frequency range the rheological data are consistent with the simple Maxwell model.

The Alignment of Lyotropic Liquid Crystals Formed by Hexadecyltrimethylammonium Bromide in D2O in a Magnetic Field

Abstract: The alignment of lyotropic liquid crystals formed by hexadecyltrimethylammonium bromide (CTAB, where C stands for cetyl) with D2O was studied by the use of 2H NMR. At CTAB/D2O concentrations between 1.01 and 1.29 mol/kg, liquid crystal domains aligned in the magnetic field within a few hours. The dependence of the characteristic alignment time on concentration and temperature has been determined. At higher concentrations, no alignment took place due to the high viscosity of the system. At lower concentrations, the alignment could not be observed by 2H NMR. The addition of sodium salicylate (NaSal), at equal molar concentrations of CTAB and NaSal, changed the orientation of the micelles from parallel to the magnetic field to perpendicular to the field. Line-shape simulations were carried out to give estimates on the rate of exchange between free D2O molecules and those bounded to the micelles, as well as on the deuterium quadrupole splittings for D2O molecules bound to micelles. The dependence of the chara...

Ferroelectricity in liquid crystals

Abstract: After summarizing ferroelectric and antiferroelectric liquid crystals (LCs) in liquid crystals so far discovered, two materials exhibiting a proper ferroelectricity are reported; (1) polar order in nematic LC of aromatic polyesters and (2) ferroelectric switching in a lyotropic liquid crystal of polypeptide. In the polypeptide LC, strong second-harmonic generation (SHG) was observed by applying an electric field, and the phase of the SH field was reversed by reversing the field, indicating the ferroelectric switching of the nonlinear polarization. SHG was also observed in the unperturbed helical state when the incident light with the wavelength the same as the helical pitch is passed through along the helical axis. In the aromatic polyester LC, SHG arises when the degree of polymerization is larger than 20. It is proposed that these polar organization originates from the dipole-dipole interaction, namely the proper ferroelectricity.

Lyotropic liquid crystals in binary systems n-alkyl glycosides/water*

Abstract: The formation of lyotropic mesophases (liquid crystals) in four binary systems n-alkyl glycosides/water was examined in dependence on surfactant concentration, temperature and the chain lengths (alkyl = heptyl, octyl, nonyl, decyl). The binary phase diagrams were established and the enthalpies of phase transitions were measured. The following phase transitions were detected by texture observation and calorimetry: hexagonal phase H, lamellar phase L, cubic phase Q, gel phase G and crystalline phase C. The positions of the corresponding regions of these phases in the phase diagram were determined. Sequence of phases and the localization of the phase regions were depended on the chain length of the alkyl group. So in the binary system n-decyl-β-D-glucoside/water the H-phase was not observed.

Time dependence of the magnetic grain concentration and secondary grain aggregation in ferronematic lyotropic liquid crystals subjected to magnetic field gradients.

Abstract: The dynamical behavior of lyotropic nematic liquid crystals doped with ionic and surfacted magnetic fluids (ferronematics) is studied using a linear optical technique. The response of these mesophases to a combination of a static and a pulsed magnetic field is investigated by measuring the relaxation times as a function of the pulse width. A reversible modification of the magnetic grain concentration in the bulk of the samples and a secondary aggregation process due to the presence of a field gradient introduced by the pulsed field is discussed.

Two-Dimensional Polymerization of Lipid Bilayers: Effect of Lipid Lateral Diffusion on the Rate and Degree of Polymerization

Abstract: Hydrated amphiphiles can yield quite complex lyotropic liquid crystals such as the lamellar (bilayer) and nonlamellar phases. Lamellar structures can be solidlike or liquid crystalline. An important characteristic of these lamellar phases is the lateral diffusion of the lipids which increases by ca. 102 at the main phase transition, Tm. The rate (Rp) and degree (Xn) of polymerization were determined for polymerizable lipids in these two phases. A determination of the effect of temperature between 25 and 45 °C on the Rp of redox-initiated polymerization of mono-SorbPC bilayers showed a discontinuity near the Tm. The calculated activation energy, Ea, and frequency factor, A, for the polymerization at temperatures below Tm are 10 kcal/mol and 107, respectively. A similar calculation for the polymerization at temperatures above the Tm gave an Ea = 24 kcal/mol and A = 1016. The degree of polymerization, relative to poly(methyl methacrylate) standards, for bilayers of mono-SorbPC at temperatures above and below...

Liquid-state theory of anisotropic flexible polymer fluids

Abstract: We extend the liquid-state theory of polymer fluids to include anisotropy as a key feature. The formalism is quite general. In determining the structure of anisotropic polymer fluids, it yields thermodynamic information as well. Our first application is to describe the nematic phases of flexible polymers, and to demonstrate a novel lyotropic transition.

Polymers in lyotropic liquid crystals

Abstract: 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.

Quantified chirality, molecular similarity, and helical twisting power in lyotropic chiral nematic guest/host systems

Abstract: Lyotropic liquid crystals can exhibit phase chirality. The mechanism behind the transfer of chirality between a chiral dopant and a liquid crystalline host phase is still under discussion. Our own recent results and proposals are the following. Lyotropic phase chirality can exist even at very low concentrations of chiral dopants, with less than 1 chiral dopant per 50 micelles. There is evidence for an intramicellar double twist which could be due to the induction of chiral conformations in the achiral surfactant chains. The chirality of arbitrary molecules can be quantified by means of the 'Hausdorff distance'. Increasing chirality of a dopant does not necessarily imply increasing helical twisting power, and molecular similarity between chiral guest and achiral host is essential for effective chirality transfer.

Study of lyotropic liquid crystal in lubrication on aluminum alloy surfaces

Abstract: The phase diagram of the system formed by diethanol ammonium dodecanoate ( DCD ) / n-butano1 / paraffin oil (LP) /water was determined The lyotropic liquid crystal region was confirmed and the use of liquid crystal as lubricant on aluminum alloy surfaces was studied. The effect of the liquid crystal structure on the tribological properties was also evaluated. Comparing the wear scar widths and the vertical loads of liquid crystal with that of a commercial grease. The lamellar liquid crystal showed a higher load carrying capacity relative to the commercial grease.

Nanophase Magnetic Materials: Synthesis and Properties

Abstract: Self-assembly preparative techniques in confined media that lead to magnetic materials with nanometer dimensions are described. Synthesis of nanoparticles using the restricted environments offered by surfactant systems such as water-in-oil microemulsions (reverse micelles) provide excellent control over particle size, inter-particle spacing, and particle shape. These environments have been used in the synthesis of γ-Fe2O3, Fe3O4, MnFe2O4, CoFe2O4, Fe and Fe/Au with particle sizes ranging from 10–20 nm. The controlled environment of the reverse micelle also allows sequential synthesis, which can produce a core-shell type structure (e.g., iron nanoparticles with gold coatings). Lyotropic liquid crystal media also offer template effects for the synthesis of non-spherical magnetic nanostructures. The structures, theory and modeling concepts and novel physical properties of these materials are discussed with emphasis given to the differences between course and fine grained magnetic materials.

Self-diffusion of a semiflexible polymer measured across the lyotropic liquid-crystalline-phase boundary

Abstract: The self-diffusion of fluorescently tagged poly(γ-benzyl-α,L-glutamate), a helical, semiflexible synthetic homopolypeptide, has been measured in isotropic and cholesteric liquid-crystalline solutions by pattern fluorescence photobleaching recovery On the isotropic side of the sharp isotropic–liquid-crystalline (ISO–LC) phase boundary, the rodlike polymers assume all possible orientations in a three-dimensional space, becoming enmeshed In liquid-crystalline solutions, as first shown by Robinson [Trans Faraday Soc 52, 571 (1956)], spontaneous alignment of the cholesteric screw axis parallel to the optical (z) axis of the instrument produces small monodomains in which parallel rodlike polymers are organized into planes Each horizontal plane is twisted slightly compared to its neighbors Over the thickness of the sample, the rodlike polymers assume all possible orientations in this two-dimensional space Despite the small size of the monodomains, it was possible to determine the self-diffusion coefficien

NMR Study of Flow and Viscoelastic Properties of PBLG/m-Cresol Lyotropic Liquid Crystal

Abstract: Director distortion patterns and backflow effects in transient flows of nematic solutions of PBLG/m-cresol are studied by deuteron NMR. The simulation of the observed NMR spectra as a function of time allows to characterise the director field pattern and to evaluate most of the viscoelastic properties of the system. A good agreement with classical rheometry is observed.

Liquid crystal polymorphism in F-actin: Optical microscopic and rotatory dispersion studies

Abstract: Filamentous actin (F-actin), which occurs abundantly and ubiquitously in living mechanisms such as muscle, nonmuscle cells, and cytoskeleton, exhibits a liquid crystal polymorphism as its concentration is increased. The double-stranded, helical F-actin filaments are 1–70 μm long in our samples. The chirality of the filaments is consistent with the experimental observation of the characteristic cholesteric fingerprint and uniform textures. In addition to the chiral nematic phase, our optical microscopic studies show the occurrence of tilted chiral smectic phases, e.g., smectic C*, I*, or F*, and a smectic B phase. Measurement of optical rotatory dispersion in the cholesteric phase confirms the prediction of the de Vries equation describing the optical rotatory dispersion behavior for cholesterics. The observed lyotropic polymorphism is consistent with the Flory lattice model and a semiflexible polymer mesogen model of F-actin.

Micellar shape anisotropy and elastic constants in discotic lyotropic liquid crystals

Abstract: The elastic constants of a discotic lyotropic nematic liquid crystal are calculated by means of a pseudomolecular approach as functions of the micellar shape anisotropy. By assuming that the temperature dependence of the ratio of the elastic constants comes from the temperature dependence of the micellar shape anisotropy, the theoretical predictions are connected with experimental measurements for the ratio ${K}_{33}{/K}_{11}.$ This procedure permits one to determine, in a phenomenological way, the temperature dependence for the ratio of elastic constants and for the micellar shape anisotropy near the nematic-isotropic transition in agreement with the experimental data.

Distinct Temperature Dependence of Cholesteric Pitch in Lyotropic Cholesteric Solutions of Polypeptide

Abstract: Distinct Temperature Dependence of Cholesteric Pitch in Lyotropic Cholesteric Solutions of Polypeptide

Development and Characterisation of Supramolecular Autovectoring System for Selective Drug Delivery

Abstract: Supramolecules since ages have been characterised as self-associating systems emanating the properties directly related to the mode of molecular association. Similar to supramolecules, liquid crystals may also be considered as an associated system. The liquid crystals are defined as the state of matter with the characterstic order of the crystal and the mobility of liquid. The system has been compared to the transporting form of cholesterol in body. The present study reports autovectoring potentials of the drug liquid crystals using diclofenac diethylammonium (DD) as a model. The drug based liquid crystals of DD were prepared employing temperature induced transformation of isotropic form to the liquid crystal form. The prepared liquid crystal systems were incubated with 1% phosphatidylcholine in order to stabilise the surface and restrict it into the liquid crystalline state. The system was characterised for viscosity variation, X-ray diffraction pattern, partitioning behaviour and in vitro diffusion profile. In vivo vectorising potential of the developed system was evaluated using rats as test animal and studying for the organ level distribution and drug compartmentalisation. The system exhibited satisfactory vecterisation as significant amount of administered dose was localised selectively in liver.

Lyotropic liquid crystalline behavior of five chitosan derivatives

Abstract: Five chitosan derivatives, ie O-butyryl chitosan, O-benzoyl chitosan, N-phthaloyl chitosan, N-maleoyl chitosan and O-cyanoethyl chitosan, were prepared from chitosan All of them had better solubilitythan chitosan, and demonstrated lyotropic liquid crystalline behavior in various solvents The critical liquidcrystalline behavior of three O-substituted chitosan derivatives was evidently different from two N-substituted analogues Typical fingerprint textures of cholesteric phase were only observed in three O-substituted derivatives The critical concentration (v/v%) of three O-substituted derivatives does not dependon the acidity of acidic solvents

Influence of the chemical nature of various geometries on the rheological behavior of a lamellar lyotropic phase

Abstract: The influence of the chemical nature of the substrate was studied in order to determine its impact on the rheological behavior of lyotropic lamellar phases Small-angle x-ray diffraction analysis established that the plastic behavior of the samples could be explained by the large disorganization of the lamellar layers in the vicinity of surfaces as stainless steel, gold, tin, copper, and bismuth On the other hand, layer alignment was almost perfect on quartz, and the lamellar samples displayed a dominant viscous behavior induced by the flow of the lamellar layers in the vicinity of the surfaces On zinc sulfide, an in between behavior was observed and the lamellar sample showed two yield stress: one is necessary to induce local alignment of layers in the vicinity of the surfaces, and the other must align the layers of the lamellar sandwich in the flow direction Assumptions as to the origin of the complex and varied organization have been studied by considering the surface free energy and the surface top

Cholesteric polymer liquid crystal-forming composition and cholesteric polymer liquid crystal

Abstract: PROBLEM TO BE SOLVED: To provide a method utilized for displaying or coloring by improving defects such that much labor is required, a fine control of its color shade is also difficult and in many cases the color is shifted from the objective color in a method of using conventional thermotropic liquid crystal and a lyotropic liquid crystal, using a material available easily and at a low cost, performing the control and fixation of the helical pitch simply and effectively and generating the objective color tone in a high definition. SOLUTION: This composition is obtained by containing a cholesteric polymer liquid crystal-forming compound containing an acyl derivative of a hydroxyalkylcellulose as a main component with an energy ray curable compound. Also, a wavelength control of the reflective light of the cholesteric liquid crystal is performed and at the same time or in succession by performing an energy ray irradiation, the cholesteric polymer liquid crystal consisting of the acyl derivative of hydroxyalkylcellulose having fixed cholesteric helical structure is obtained.