Intermediate Mesophase Research Articles

Engineering the Thermodynamic Stability and Metastability of Mesophases of Colloidal Bipyramids through Shape Entropy.

We report several types of entropy-driven phase transition behaviors in hard bipyramid systems using Monte Carlo simulations. Bipyramidal nanoparticle shapes are synthesizable from gold and silver, with sizes ranging from tens to hundreds of nanometers. We report numerous colloidal crystalline phases with varying symmetries and complexities as the bipyramid aspect ratio and base polygon are varied. Some bipyramids are mesogenic and undergo either monotropic or enantiotropic phase transitions. We show that such mesophase behavior can be modulated by tuning the bipyramid aspect ratio. In addition, we report stepwise kinetic crystallization and melting pathways that occur via an intermediate mesophase as the system gains or loses order in successive stages. Our results demonstrate that complex phase transition behavior involving mesophases can be driven by entropy alone. Importantly, our results can guide the synthesis of bipyramid shapes able to assemble target structures and can be used to engineer the kinetic pathways to and from those structures to involve or avoid mesophases.

Structural transformations and phase transitions in hexagonal La-containing lyomesophases

Understanding and identification of phase equilibrium in self-assembling systems like lyotropic liquid crystals (LLCs) plays a key role in their further practical applications. In this study the phase transitions in LLCs based on С12ЕО10 nonionic surfactant, lanthanum nitrate hexahydrate, and water are reported. Polarized optical microscopy, X-ray powder diffraction, and fluorimetry were used to find correlations between system composition and structural changes. A new approach to identify a reverse hexagonal mesophase by the analysis of concentration dependencies of mesophase structural parameters was proposed. Data from these experiments were further compared with pyrene fluorescence studies to confirm the phase inversion. Based on complex analyses of experimental data an inversion of hexagonal mesophases via intermediate lamellar phase in the С12ЕО10(LaIII)/H2O system was found at the concentration ratio of 85/15 wt.%. The interpreted temperature-composition phase diagram was plotted. The regions of existence of direct hexagonal, intermediate mesophases and reverse hexagonal were found in the С12ЕО10(LaIII)/H2O system.

MESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATESMESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATES

Phase equilibria in binary systems of individually non-mesomorphic components: propionates, isobutyrates, butyrates and valerates of cesium and barium at temperatures from 20 to 400 °C have been investigated by the me­thods of differential thermal analysis and polarization polythermal microscopy. In all systems, the formation of intermediate li­quid-crystalline solutions of smectic modification (type A) was established. The tempe­rature-concentration regions of the formation of ionic liquid crystals and glasses are determined. The studies carried out show that in binary systems of cesium and barium alkanoates interme­diate liquid-crystal solutions are generated due to the latent mesomorphism of the correspon­ding cesium alkanoate and due to the eutectic decrease in liquidus temperatures in the binary systems. The thermal stability of the induced mesophase in the case of systems of the consi­dered type is influenced by the following factors: the degree of ordering of the melt, which correlates with the length of the alkyl chain of the alkanoate anion, and a decrease in the temperatures of the liquidus line relative to the latent clearing temperature. The possible influence of compounds melting congruently or incongruently, formed in binary systems, should also be taken into account. Experimental data indicate the largest temperature-concentration range of the mesophase in the butyrate system, where there are the most favorable conditions for the implementation of intermediate li­quid crystal solutions. Such conditions are the lar­gest decrease in liquidus temperatures in a series of systems relative to the latent clearing point, as well as an additional increase in thermal stability due to the formation of a congruently melting compound of anisometric structure. In the case of the valerate system, a certain increase in anisotropy in comparison with the butyrate system is leveled by high liquidus temperatures; here is the narrowest region of existence of the intermediate mesophase due to its thermal destabilization.

Structural analysis of nanoparticulate carriers for encapsulation of macromolecular drugs

Recently developed macromolecular drugs display strong potential to cure diseases involving genetic components, e.g. Rheumatoid arthritis, diabetes, Alzheimer's disease, Huntington's disease, Duchenne muscular dystrophy, Retinitis pigmentosa, and several types of cancers. Bioavailability and enhanced drug specificity necessitate the preparation of efficient carrier systems for the macromolecular therapeutics. We employ synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-TEM) to study the nanostructure formation, macromolecular drug upload, and the topological transformations occurring upon complexation of supercoiled plasmid DNA (encoding for the therapeutic protein brain-derived neurotrophic factor, BDNF) with cationic lipid nanocarrier assemblies. Understanding of the liquid crystalline nanostructure formation (hexosomes, cubosomes, inverted hexagonal and intermediate mesophases, or onion-type complexes) enabling efficient delivery of new generation sequencing systems is expected to contribute to the progress in precision nanomedicine and the treatment of various severe diseases.

Inductive effect of crystalline nucleus on the structure of its local environment in the process of quartz glass crystallization

The morphology and the structural and chemical properties of crystalline formations appearing on the surface of commercial quartz glasses at the beginning of the induction stage upon heating at temperatures of 1000–1300°C are studied by optical polarization microscopy, μ-Fourier transform infrared spectroscopy, and X-ray diffraction. It is shown that crystalline island nuclei induce crystallization not only in the local environment of the surface layer, but also in the glass bulk at a depth of up to ≈200 μm. Crystalline nuclei in the center of islands often have an imperfect crystal structure formed by intermediate mesophases based on individual low-symmetry SiO4 tetrahedra. However, the induced phase at the periphery of these nuclei has a well-ordered crystal structure consisting mainly of α-SiO2 (quartz) and/or α-cristobalite. The proportion of these two phases depends on the glass heating temperature, namely, at 1000°C, the induced structure for the most part contains α-SiO2, while α-cristobalite dominates at 1300°C.

Low shear rheological behaviour of two-phase mesophase pitch

The low shear rate rheology of two phase mesophase pitches derived from coal tar pitch has been investigated. Particulate quinoline insolubles (QI) stabilised the mesophase spheres against coalescence. Viscosity measurements over the range 10–106Pas were made at appropriate temperature ranges. Increasing shear thinning behaviour was evident with increasing mesophase content. At low mesophase contents the dominant effect on the near Newtonian viscosity was temperature but at higher contents it was the shear rate; temperature dependence declined to near zero. The data indicated that agglomeration could be occurring at intermediate mesophase volume fractions, 0.2–0.3. The Krieger–Dougherty function and its emulsion analogue indicated that in this region the mesophase pitch emulsions actually behaved like ‘hard’ sphere systems and the effective volume fraction was estimated as a function of shear rate illustrating the change in extent of agglomeration. At the higher volume fractions approaching the maximum packing fraction, which could only be measured at higher temperatures, the shear thinning behaviour changed in character and it is considered that this is possibly due to shear induced deformation and breakup of dispersed drops in the shear field.

MeV-Proton Induced Effect on Mesophase Structure of Polyethylene Terephthalate

High crystalline polyethylene terephthalate (PET) microfibres were irradiated (at low energy density regime, De ~10 23 eV/cm) with 2.4 MeV proton beam at 3 different fluences: 1×10 p/cm,1×10 p/cm and 1×10 p/cm. Because of irradiation, the fibre gets amorphized from its highly crystalline state after passing through an intermediate mesophase stage. The mesophase of polymers is well studied using wide-angle X-ray scattering, small-angle X-ray scattering, FTRaman scattering and nuclear magnetic resonance techniques. In the present paper, ion (proton) induced mesophase structure of PET was observed. X-ray fiber diffraction was carried out by adopting a special fiber mounting technique and using a diffractometer having Bragg-Brentano parafocusing optics. The sample irradiated at the lowest fluence showed the maximum percentage (7.05%) of mesophase.

Toward understanding the evolution of griseofulvin crystal structure to a mesophase after cryogenic milling

The purpose of this research is to investigate the response of crystalline griseofulvin to mechanically induced stress through cryogenic milling. Crystalline griseofulvin was subjected to cryogenic milling for two different lengths of time. Following cryo-milling, the samples were immediately analyzed by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD). The DSC thermograms of cryo-milled griseofulvin showed a complex exothermic event at around 65 °C for the 30 min cryo-milled sample and around 75 °C for the 60 min cryo-milled sample. A glass transition event was not observed for the cryo-milled samples. This is in direct contrast to the X-ray amorphous griseofulvin sample prepared through the quench melt method The XRPD patterns of cryo-milled griseofulvin show a loss of the crystalline Bragg peaks and a corresponding increase in diffuse scattering (halos). The disordered griseofulvin material produced through cryo-milling appears X-ray amorphous, yet different from the amorphous phase produced using the quench melt method. Both X-ray amorphous materials have distinctive DSC thermograms and X-ray powder patterns. These findings suggest that the evolution of the griseofulvin crystal structure during cryo-milling is not simply a crystal-to-amorphous transition but a transition to an intermediate mesophase.

On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac

An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q L , consists of discrete discontinuous micelles arranged in a cubic array. The Q L phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q L structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > 1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase ( L α ). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At ⩾ 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.

Reversible melting of high molar mass poly(oxyethylene)

The heat capacity, C p , of poly(oxyethylene), POE, with a molar mass of 900,000 Da, was analyzed by temperature-modulated differential scanning calorimetry, TMDSC. The high molar mass POE crystals are in a folded-chain macroconformation and show some locally reversible melting, starting already at about 250 K. At 335 K the thermodynamic heat capacity reaches the level of the melt. The end of melting of a high-crystallinity sample was analyzed quasi-isothermally with varying modulation amplitudes from 0.2 to 3.0 K to study the reversible crystallinity. A new internal calibration method was developed which allows to quantitatively assess small fractions of reversibly melting crystals in the presence of the reversible heat capacity and large amounts of irreversible melting. The specific reversibility decreases to small values in the vicinity of the end of melting, but does not seem to go to zero. The reversible melting is close to symmetric with a small fraction crystallizing slower than melting, i.e., under the chosen condition some of the melting and crystallization remains reversing. The collected data behave as one expects for a crystallization governed by molecular nucleation and not as one would expect from the formation of an intermediate mesophase on crystallization. The method developed allows a study of the active surface of melting and crystallization of flexible macromolecules.

Polymorphic Transitions Induced by Annealing in Stretched Fibers of Syndiotactic Polypropylene

A study of the polymorphic transitions induced by annealing of fibers of syndiotactic polypropylene initially in the trans-planar form III and in the mesomorphic form is reported. Both the trans-planar form III and the mesomorphic form transform by annealing at high temperatures into a mixture of crystals of the antichiral helical form I and the isochiral helical form II. Annealing of the trans-planar mesomorphic form produces simultaneous formation of the isochiral form II and the antichiral form I, already at low temperatures (40−60 °C). The relative amounts of forms I and II increase with increasing the annealing temperature and fibers containing similar amounts of crystals of forms I and II are obtained at high temperature (120−130 °C). Fibers of the crystalline trans-planar form III transform mainly into the antichiral form I by annealing up to 80 °C. At higher temperatures also the isochiral form II develops, and fibers in a mixture of similar amounts of crystals of both helical forms are obtained at 120−130 °C. These results indicate that the formation of the isochiral helical form II is not necessarily linked to the presence of the trans-planar mesomorphic form, as suggested in the literature, but it can be obtained also starting from the crystalline form III. These experimental data are not consistent with the hypothesis reported in the literature that intermediate mesophases are necessarily precursors of the crystallization of the isochiral structure of syndiotactic polypropylene.

Controlling Nanopore Size and Shape by Fluorosurfactant Templating of Silica

Fluorinated surfactants are a special class of surfactants that assemble into aggregates and form novel intermediate mesophases more easily than hydrocarbon surfactants. Despite their unique properties, researchers have only recently begun to explore the use of these surfactants as templates for porous inorganic materials. Here, we report a comprehensive investigation of the use of cationic fluorinated surfactants as templates for ordered nanoporous silica. A homologous series of perfluoroalkylpyridinium chloride surfactants with tail lengths between 6 and 12 carbons is synthesized and characterized. Using these surfactants in aqueous solution, materials are synthesized with pore structures that, as the tail length of the surfactant increases, include uniform wormhole-like pores, ordered 2-D hexagonal pores, and mesh phase pores. The smallest pore diameter observed in this series (2.19 nm by the KJS method) is among the smallest observed for a porous ceramic made with a single chain cationic surfactant. T...

Synthesis, spectral properties and thermal behaviour of zinc(II) acetylsalicylate

The thermal behaviour of zinc(II) acetylsalicylate [Zn(acsa) 2(H 2O) 2] with respect to phase transitions, pyrolysis both in air and inert (N 2) atmosphere, and product identification has been investigated. The complex was synthesised by metathesis in hot ethanol solution using aspirin (acetylsalicylic acid) as precursor and characterised via electronic and IR spectral analyses. Optical observations showed that the white salt does not undergo a direct transition from the solid to the liquid phase but rather goes slowly through an intermediate mesophase around 80 °C before melting rapidly to the brick-brown isotropic liquid around 134–136 °C. No liquid crystalline phases are however formed. This result was complemented by that from thermogravimetric (TG) studies in the ca. 25–600 °C range, which showed three main weight-loss phases of 8.0, 50.0 and 14.0% (around 200, 250 and 400 °C) corresponding, respectively, to the elimination of CO 2, xanthone and acetic acid. The pyrolysis products, as identified using a combination of instrumental (GC–MS) and wet chemical techniques are: CO 2; non-stoichiometric zinc oxide, most likely in the form: Zn 1+ x O (where 0.0000≤ x≤0.0003); and a mixture of organic products resulting from further decomposition, charring and other attendant thermal effects at the relatively high temperatures (ca. 600 °C) involved. Six of the principal organic products were identified and included salsalate and benorylate which are pro-drugs of salicylic acid, a well-known pharmaceutical.

Studies of the mesophase development in polymeric fibers during deformation by synchrotron SAXS/WAXD

On-line structural and morphological studies on Kevlar 49 and isotactic polypropylene (iPP) fibers during deformation were carried out using synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). A novel image analysis method was used to extract quantitative fractions of the crystal phase, the amorphous phase and a “mesomorphic” (intermediate) phase from two-dimensional (2D) WAXD patterns. Results showed that about 20 wt% in the Kevlar 49 fiber had an intermediate mesophase morphology. The transitions between crystal phase, amorphous phase and mesophase were not obvious during deformation of Kevlar 49 fiber at room temperatures. 2D SAXS patterns indicated that the superstructure of the Kevlar 49 fiber was fibril in nature. 2D WAXD results of iPP fibers showed that the α-form crystals were quite defective in the initial state and were converted to the well-known mesomorphic form by drawing at room temperatures. The mesophase in Kevlar 49 fibers was then compared with that in iPP fibers. The shape of one-dimensional equatorial peak of the mesophase in the iPP fiber was similar to that in the Kevlar fiber, indicating that the mesophase in both iPP and Kevlar fibers could be similar in some aspects of molecular arrangement. Corresponding 2D SAXS patterns showed that there was no obvious long period in the mesophase of the drawn iPP fiber. We speculate that the constituents of the mesomorphic fraction extracted in the drawn iPP fibers may consist of partially oriented bundles of helical chains with random helical hands as well as oriented chains with no helical structures (consisting of stereo/tacticity defects). The latter is similar to the mesophase of rigid chains in Kevlar fibers, consisting of only oriented chains with no helical structures.

From Cylinders to Bilayers: A Structural Study of Phase Transformations in a Lyotropic Liquid Crystal

Abstract The structural relations of the four intermediate mesophases between the hexagonal phase and the lamellar phase of the sodium dodecyl sulfate-water system are examined. The system manages to cross from a situation with homogeneously curved interfaces (cylinders) to another one with zero curvature (bilayers) in a nearly continuous way. The first step is the transformation of the cylinders into ribbons; then the ribbons become connected to each other at regular intervals to form a three-dimensional array of rods. Subsequently this array is distorted to give a layered structure where the layers are spaced as in a lamellar phase but retain the correlations of the cubic phase in the other directions. The final step is the transition to a system of flat layers. The only physical parameter which appears to change in consistent way through this series of structures is the mean curvature of the interfaces. Comparison with other systems which adopt different solutions to transform a cylinder into a bilayer...

Phase diagram of sodium dodecyl sulfate-water system: 1. A calorimetric study

The phase diagram of sodium dodecyl sulfate (SDS)-water system is established from differential calorimetric measurements. The SDS purification and the absence of degradation was checked using NMR analysis before and after the calorimetric recordings. Thermodynamic equilibrium of mixtures was achieved by using low heating rates (0.08°C/min). A quasi-continuous exploration of the phase diagram (0.2 wt% per step) with accurate temperature and enthalpy measurements allows precise determination of the complicated intermediate mesophase region. Six invariant reactions are identified. Temperatures of five of them are separated by small intervals (from 0.2 to 5°C). Tammann representations of enthalpies precisely determine the eutectoid and monotectoid compositions and invariant limits. In the surfactant-rich region, all the invariant limits appear at the same molar ratio: SDS/2 D 2O, while the high hydration limits are located within a small composition range (from 57.1 to 66.4% SDS). Their enthalpies and entropies are discussed in relation to the mesophase structures and topology changes. The description of the surfactant-rich region is attempted. A dihydrate not previously reported is found. The freezing of water is also examined, and three types of water interactions are observed.

Between cylinders and bilayers : structures of intermediate mesophases of the SDS/water system

The classical geometries for the packing of amphiphile molecules in the ordered phases of lyotropic systems are the lamellar phase where bilayers of amphiphilic molecules are separated by water layers, and the hexagonal phase where cylinders of amphiphile are arranged on a two-dimensional hexagonal lattice. These phases only exist for definite compositions of the water/amphiphile system; in between them, there usually lies a vast concentration region which allows the system to cross from zero curvature (bilayers) to finite curvature (cylinders). The problem with such intermediate regions is that they may contain a large number of mesophases, each limited to a very narrow range of compositions (∼1%). To solve this problem we deliberately create a spatial gradient in the concentration of water/amphiphile of each sample; such samples are scanned by the X-ray beam of a synchrotron source, allowing diffraction patterns to be recorded at concentration intervals ∼0.05%. For the system SDS/water we have identified 4 intermediate mesophases: a tetragonal phase, a cubic phase, a rhomboedral phase and a two-dimensional monoclinic phase. These structures show that the system manages to cross from a planar geometry to a cylindrical geometry in a nearly continuous way Identification de 4 mesophases intermediaires pour le systeme SDS/eau: quadratique, cubique, rhomboedrique et monoclinique bidimensionnelle. Ces structures montrent que le systeme peut passer d'une geometrie planaire a une geometrie cylindrique de maniere quasiment continue