Neat Phase Research Articles

Investigations of the high-pressure phase behaviour of thallium(I) tetradecanoate at pressures up to 250 MPa

High-pressure phase equilibria for thallium(I) tetradecanoate at pressures up to 250 MPa are presented. At normal pressure thallium(I) tetradecanoate exhibits three additional phases at temperatures below the range of stability of the neat phase. In contrast to the phases II and III as well as the neat phase, phase I is pressure-limited and no longer stable at pressures above 75 MPa.

The role of partial miscibility on the properties of blends of a polyetherimide and two liquid crystalline polymers

This paper is concerned with the existence of partial miscibility of a polyetherimide (PEI) with both amorphous and semicrystalline liquid crystalline polymers (LCPs) and its effect on the morphology of the blends of these polymers. Partial miscibility was determined by measuring the shift in the glass transition temperatures as determined by dynamic mechanical thermal analysis and differential scanning calorimetry. With increasing concentration of the LCP in the PEI/LCP blends, the glass transition temperature of the PEI phase shifted to a lower temperature. Annealing and mixing history were also observed to affect the degree of shift in the glass transition temperature. Morphologies of the partially miscible systems were found to be quite different from those of an immiscible system. It is likely that due to partial miscibility in these blends, a PEI-LCP solid solution coexists with the neat LCP phase.

Oxidative Stability of Polyunsaturated Fatty Acids in an Aqueous Solution

The relative oxidative stability of six kinds of typical polyunsaturated fatty acids (PUFAs) was investigated in an aqueous solution (pH=7.4 at 37°C) with Fe2+-ascorbic acid as a catalyst. The highest stability was shown by docosahexaenoic acid (22: 6n-3, DHA), followed by eicosapentaenoic (20: 5n-3), arachidonic (20: 4n-6), α-linolenic (18: 3n-3), γ-linolenic (18: 3n-6), and linoleic (18: 2n-6, LA) acids, indicating that the stability increased with increasing degree of unsaturation. The significant difference found between α-linolenic and γ-linolenic acids also suggests the higher oxidative stability of n-3 PUFAs than of n-6 PUFAs in an aqueous solution. Moreover, when a mixture of DHA and LA was oxidized in an aqueous solution, the stability increased with increasing molar ratio of DHA to LA in the mixture. This characteristic oxidative stability of PUFAs in the aqueous phase is quite different from that in the neat phase, and can be explained by correlating with the conformation of PUFAs in the aqueou...

Patterns of Change and Continuity in Nineteenth-Century Warfare

This chapter presents an analysis and synthesis of the Napoleonic Wars and the wars of the nineteenth century. The traditional view of warfare in the nineteenth century divides it into several distinct and neat phases with their evolution clearly defined. There was significant evolution and change during the Napoleonic Wars, and there are more similarities than differences between Napoleonic warfare and warfare in the mid-nineteenth century. The process begins with Napoleon. Napoleonic warfare is characterized by the French use of the army corps system and decisive victories in which the opposing armies are destroyed in one big battle, usually lasting a single day. For the campaign in 1805, Napoleon sought a strategic envelopment of the Austrian field army operating on the upper Danube. At the outset of the campaign, both the Napoleonic and Russian forces were organized into distinct field armies.

Cation-exchange liquid chromatography of choline and acetylcholine on free shielded silanols of silica-based reversed-phase stationary phases

Free anionic functions present on the surface of reversed-phase packing materials were used for the selective cation-exchange preconcentration and separation of the neurotransmitters choline and acetylcholine from a biological matrix. The cation-exchange behaviour of different reversed-phase packing materials in the neat aqueous mobile phase, the properties of an end-capped column, the dependence of capacity factors and peak shape on the concentration of counter ions, ionic strength, pH and the addition of acetonitrile and optimum conditions for enzymatic conversion of solutes to hydrogen peroxide were studied. The studied reversed-phase columns exhibit better pH stability and longer lifetimes than normal silica-based cation exchangers. Acetylcholine is an effective and sensitive test sample for the measurement of adsorption on silica support. A large sample volume was injected onto a precolumn inserted instead of an injection valve and after injection the solutes were focused and separated on an analytical column with a mobile phase containing tetramethylammonium perchlorate as the counter ion.

X-ray diffraction studies on homologous thallium soaps below the temperature range of the neat phase 2. Structure models of crystalline modifications in the temperature range below the neat phase

In Part 1 were discussed the results of X-ray diffraction measurements on homologous thallium soaps, the lattice parameters and the unit cells of the different phases: phase C1, phase C2, phase I, phase II, and the neat phase. The aim of Part 2 is the development of structural models, based on data on lattice parameters, packing densities of hydrocarbon chains and head groups. In order to supplement our experimental data we carried out infrared-spectroscopic measurements at different temperatures within the existence regions of these phases to get additional information on alterations in configurations of head groups and hydrocarbon chains of thallium soaps in these phase regions. By comparing the structural models we can generalize that the phase C1, phase C2, phase I, and phase II have some properties in common: they form crystalline structures, their unit cells are monoclinic, and the angles α and β are orthogonal. The amount of the lattice parametersc is equal to the distances of two molecular bilayers and/or twice the distance between the lamellae. Among the normal lamella, the molecules form a “herring-bone-like” packing. This indicates that the lamellar structure of the liquid-crystalline neat phase is already preformed in these crystalline modifications of phase C1, phase C2, phase I, and phase II. These crystalline phases differ in their lattice parameters and their packing coefficients. The transition from the crystalline phase I or phase II into the neat phase is accompanied by a temperature-dependent contraction of the distances between the lamellae, which originates in the “fluidity” of the hydrocarbon chains. Simultaneously, the lattice parametersa andb are drastically shortened and attain dimensions considerably lower than the values obtained in crystalline modifications. The X-ray scattering properties of the Tl+-ions suggest that the Tl+-ions exist in a “fluid-like” state within the head groups region of the neat phase. We came to the conclusion that the thallium-oxygen-bond is remarkably less polar than the bonds between alkali ions and oxygen resulting from the electro-negativity of the metal-oxygen-bonds of the alkali soaps, in comparison to the thallium soaps. Hence, the absence of polymorphic liquid-crystalline semiphases of thallium soaps is due to the low polarity of the thallium-oxygen-bond. Structure formation of Tl-soaps is mainly influenced by the hydrocarbon chain packing.

X-ray diffraction studies on homologous thallium soaps below the temperature range of the neat phase 1. Calculation and comparison of the structure parameters of unit cells

The results of X-ray diffraction patterns of homologous thallium soaps TlCn (n-8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20 and 22) in dependence on the temperature showed that the structures of the phases below the temperature range of the liquid-crystalline neat phase (so called phase C1, phase C2, phase I, phase II) are crystalline-like, not liquid-crystalline.

Molecular flexibility in nematics: from alkanes to dimer mesogens

The ‘chord model’ of flexible alkane solute ordering in the nematic phase (D. J. Photinos, E. T. Samulski and H. Toriumi, J. Phys. Chem., 1990, 94, 4688; 4694) is extended to dimer molecules. Using the same parametrization of the modular potential of mean torque that successfully describes alkane solutes in the nematic field and monomer mesogens in neat phases, we are able to generate correctly the segmental orientational ordering profiles of a variety of mesogenic and non-mesogenic dimer solutes in a nematic solvent. The effects of the linkage between the mesogenic core and flexible spacer on the ordering properties of the dimers are explored by studying the homologous series of cyanobiphenyl (CB) ethers, CBO—(CH2)N—OCB, (N= 2–10) with different primary structural topologies, i.e. with para, meta and ortho linkages. The observed 2H-NMR spectra of para-linked dimers with N= 9, 10 and of ortho-linked dimer with N= 10 are readily reconstructed using the simplest parametrization of the chord model potential. This parametrization is then used to predict the 2H-NMR spectra of the respective meta-linked dimers and also to make inferences about how the propensities of the topologically different series of dimers for conforming to the nematic field depend on spacer length and spacer parity. Finally, the effect of the core size on the overall ordering of dimers is studied by considering para-cyanophenyl (CP) ether linked dimers, CPO—(CH2)N—OCP. It is found that, although the NMR spectra of the spacer chain in the CPO dimer series are not profoundly different from those of the respective CBO dimers, the average value of their orientational energy is indicative of substantially reduced (self) orientability of these dimers. Generally, these findings corroborate the predictive power of the chord model and its utility for describing orientational ordering of flexible solutes, even when molecular topology is complex.

Interpretation of small-angle x-ray scattering intensity distribution from fluctuating lamellae in a ternary system: sodium octyl sulfate-water-decanol

We have observed a clear small-angle X-ray scattering (SAXS) signal from a ternary surfactant-water-alcohol liquid mixture in a lamellar neat phase and have attributed the origin of the small-angle scattering to the fluctuation of the surfactant-alcohol bilayers.

Molecular flexibility and orientational ordering of nematic liquid crystals

The ‘‘chord model’’ of flexible alkane solute ordering in the nematic phase [D. J. Photinos, E. T. Samulski, and H. Toriumi, J. Phys. Chem. 94, 4688 (1990); 94, 4694 (1990)] is extended to prolate mesogen molecules with a single alkyl tail, and the physical properties of two homologous series, 4,4′-n-alkylcyanobiphenyls and 4,4′-n-alkyloxycyanobiphenyls, in neat nematic phases are evaluated. The chord model of the mesogen’s anisotropic interactions yields a consistent description of the essential features of the chain order profile (derived from deuterium nuclear magnetic resonance) and the even–odd variation of thermodynamic quantities associated with the nematic–isotropic transition. Very accurate agreement with experimental observations is obtained using the standard rotational isomeric state description of the tail–chain’s flexibility along with a minimal form of the self-consistent anisotropic potential (i.e., only two coupling constants determine the strength of orientation dependent interactions, one for the biphenyl core and one for the aliphatic chord segments). There is remarkable compatibility among the values of optimized coupling constants obtained from modeling the chain segmental order parameters and the mesophase transition temperatures. Moreover, these coupling constants evaluated for aliphatic chord segments in the neat mesogens show quantitative agreement with the values obtained for simple alkane solutes in nematic solvents. These findings suggest that the chord model, which explicitly represents molecular shape anisotropy (excluded volume effects) in conjunction with molecular flexibility, provides a very good description of complex molecules in liquid crystals.

A new model for pressure-induced shifts of electronic absorption bands as applied to neat carbon disulfide and carbon disulfide in n-hexane and dichloromethane solutions

The authors propose a model for the pressure dependence of electronic absorption spectra and apply it to the authors data on CS{sub 2} both in neat phase and in hexane and dichloromethane solid solutions. They believe that their data represent a rather severe test of this model and argue that any model for the pressure dependence of electronic absorption spectra must include certain minimal effects - dispersive or dielectric and repulsive or volume effects - in order to adequately represent the data. They discuss previous models at some length in order to delineate the limits of their applicability. They further acknowledge and define the limits of the applicability of their model to solvent-induced shifts in general.

Infrared and Raman spectra of bis(fluorocarbonyl) disulphide, [FC(O)]2S2

AbstractIR data for gaseous, liquid, solid and matrix isolated bis(fluorocarbonyl) disulphide together with the Raman spectrum of the liquid suggest the existence of two planar conformers (I and II) in equilibrium in the gaseous phase and of a planar one and other conformers of undetermined structure in the other neat phases. Wavenumbers reported for the vibration of conformer I are used to calculate an approximated force field.

Repulsive interactions between uncharged bilayers. Hydration and fluctuation pressures for monoglycerides

Pressure versus distance relations have been obtained for solid (gel) and neat (liquid-crystalline) phase uncharged lipid bilayers by the use of x-ray diffraction analysis of osmotically stressed monoglyceride aqueous dispersions and multilayers. For solid phase monoelaidin bilayers, the interbilayer repulsive pressure decays exponentially from a bilayer separation of approximately 7 A at an applied pressure of 3 x 10(7) dyn/cm2 to a separation of approximately 11 A at zero applied pressure, where an excess water phase forms. The decay length is approximately 1.3 A, which is similar to the value previously measured for gel phase phosphatidylcholine bilayers. This implies that the decay length of the hydration pressure does not depend critically on the presence of zwitterionic head groups in the bilayer surface. For liquid-crystalline monocaprylin, the repulsive pressure versus distance curve has two distinct regions. In the first region, for bilayer separations of approximately 3-8 A and applied pressures of 3 x 10(8) to 4 x 10(6) dyn/cm2, the pressure decays exponentially with a decay length of approximately 1.3 A. In the second region, for bilayer separations of approximately 8-22 A and applied pressures of 4 x 10(6) to 1 x 10(5) dyn/cm2, the pressure decays much more gradually and is inversely proportional to the cube of the distance between bilayers. These data imply that two repulsive pressures operate between liquid-crystalline monocaprylin bilayers, the hydration pressure, which dominates at small (3-8 A) bilayer separations, and the fluctuation pressure, which dominates at larger bilayer separations (greater than 8 A) and strongly influences the hydration properties of the liquid-crystalline bilayers. Thus, due primarily to thermally induced fluctuations, monocaprylin bilayers imbibe considerably more water than do monoelaidin bilayers. For both monoelaidin andmonocaprylin, the measured magnitude of the hydration pressure is found to be proportional to the square of the dipole potential.

Neat and admixed mesomorphic polysiloxane stationary phases for open-tubular column gas chromatography

A mesomorphic polysiloxane (MEPSIL) solvent, employed either neat or in admixture with SE-30 poly(dimethylsiloxane) (PDMS) diluent, is shown to be a highly selective stationary phase for open-tubular column gas-liquid chromatography. Mixtures of cis and trans fatty acid methyl esters (FAME) are resolved isothermally in under 10 min with neat nematic MEPSIL phase, where trans isomers are retained longer than their cis counterparts. Programmed-temperature separations of more complex mixtures of FAME solutes also demonstrate that elution order is by increasing carbon number and that within a group of the same carbon number, retentions increase with increasing saturation, which is completely opposite to the order of selectivity given by conventional phases. Shape selectivity of the nematic MEPSIL phase is further illustrated by the separation of samples containing polychlorinated biphenyl (PCB) solutes, where inter alla congener 198 elutes well before 128. Blending the MEPSIL solvent with SE-30 is then shown not to depress significantly the nematic/isotropic transition of the pure mesomorph, and blends of up to 3:1 SE-30/MEPSIL are virtually as selective as neat MEPSIL at temperatures in excess of 300/sup 0/C. However, the crystal/nematic transition cannot thereby be lowered substantially, nor can the lower limiting chromatographic efficiency be improved to much beyondmore » that of the neat phase. Even so, blended-phase columns exhibit in excess of 3200 N m/sup -1/ at elevated temperatures, which is sufficient to provide good resolution, isothermally, of 8 of 10 methylbenz(a)anthracene isomers at 240/sup 0/C, and of 9 of 10 methylbenzo(a)pyrene solutes at 275/sup 0/C.« less

Thermotropic Ionic Liquid Crystals VI. Structural Parameters of Solid and Liquid Crystal Phases of Anhydrous Short-Chain Sodium Alkanoates

Abstract Unit cell constants were determined from powder X-ray diffraction photographs taken of several anhydrous short-chain sodium alkanoates at room temperature. The temperature dependence of the bilayer spacing in the alkanoates was determined over the range 25-300°C. Overall changes in bilayer spacings between the solid and the neat phase were found to be much smaller than in long-chain alkanoates. A correspondence was noted between the room temperature lateral packing area and the 23Na quadrupole coupling constant in the mesophase. The mcsophase bilayer spacing was consistent with a structural model in which the tilted anion chain rotates on a cone.

Thermotropic ionic liquid crystals. VII. Calculation of sodium-23 quadrupole coupling constants in lamellar phases of sodium alkanoates

The 23Na quadrupole coupling constants (QCC) were calculated for a quasicrystalline model of the neat phase of anhydrous amphiphiles. The magnitude of the QCC in short-chain sodium alkanoates and its dependence on the lateral packing area of the polar heads was accurately predicted by assuming the charges to lie in a double-layered square array of interdigitated ion pairs.

Electrochemistry in Liquid Crystals: Orientational Effects in Electrochemical Processes

The electrochemical characterization of the room temperature nematic phases of MBBA (p‐methoxybenzilidene p‐butyl aniline), MBAB (methoxy‐butyl azoxybenzene), and K‐15 (4‐pentyl‐4′ cyano‐biphenyl) has been performed in acetonitrile, as well as in the neat phases, and it is found that they all possess a wide range of potentials over which electrochemical experiments can be carried out. MBBA and MBAB exhibit large ohmic drops making experimentation difficult. K‐15, on the other hand, proved to be very well behaved. A number of model redox couples were investigated in K‐15, and it is found that the electrochemical response can be significantly different from that observed in conventional solvents such as acetonitrile. These differences can be ascribed to the formation of ion aggregates as well as to differences in diffusion coefficients. We also present some preliminary findings on the effect of orientation on the observed electrochemical response of TCNQ (tetracyanoquinodimethane), ferrocene, and TCNE (tetracyanoethylene).

Thermal Phase Behaviour of Thallium (I) Branched Alkanoates—Influence of Chain Length and Position of Branching on the Occurrence of the (Anhydrous) Neat Phase

Abstract The thermotropic phase behaviour of anhydrous thallium (I) salts of branched chain aliphatic carboxylic acids was investigated by means of DSC and optical polarisation microscopy. The influence of the alkyl chain length and position of branching on the thermotropic phase behaviour was studied. The salts of α-branched acids did not show a stable neat phase. Salts which are alkyl substituted in the β and higher positions do however show stable neat phases. These results are compared with those found for alkali metal alkanoates.

Thermotropic Mesophases of the C8, C10, C12and C16n-Alkyl Ammonium Chlorides

Abstract Liquid crystalline and solid phases of the title compounds were studied by optical microscopy, differential scanning calorimetry and X-rays. Transition temperatures, heats and layer spacing were determined. In all the compounds the isotropic liquid is preceded by a neat (bilayer smectic A) phase, which in turn is preceded hy an intermediate phase which is separated from the room temperature crystalline phase phase by 2 to 4 first order phase transition. The intermediate phase has a structure consisting of disordered hydrocarbon chains held in place by their ionic heads (-NH3 +), with the chains perpendicular to the ionic layers. This phase which is shown to be uniaxial by convergent light observations, may be best described as also being a liquid crystal.

Lateral chain packing in lipids and membranes

The aliphatic chains of many biologically important lipids are heterogeneous and often related to the functions of the molecules. Certain phospholipids containing arachidonic acid may serve as precursors for prostaglandins, certain diglycerides may serve as second messengers for certain membrane-triggered reactions (43), and other phospholipids containing a very short chain in the two position may serve as vasoactive hormones (44). The packing of such molecules is of interest. The evidence is quite clear from both the conformation of saturated and unsaturated molecules and from mixing experiments in the solid state that long and short chains don't mix well, nor do unsaturated and saturated chains, even if they are of the same chain length. There is even some evidence to indicate that some degree of chain segregation occurs even in the liquid state. However, different chains are often associated through covalent bonds, e.g., in wax esters, diacylglycerols, triacylglycerols, and phospholipids. A variety of possibilities for chain segregation are present in the neat phases of wax esters, ceramides, diacylglycerols, and triacylglycerols. However, in the unique case of membrane lipids like phospholipids or sphingolipids, the two chains are forced to lie side by side by virtue of the interaction of the polar group with water, and thus interactions between different chains must occur. Most of the evidence suggests that, when a solid phase results in these systems, the nonspecific chain packing mode (hexagonal chain packing) is preferred. In fact, for all of the phospholipids studied thus far, clearcut evidence of specific chain-chain interaction in molecules having both unsaturated and saturated chains has never been observed. However, for mixed chain triacylglycerols, evidence of specific chain-chain interactions (beta' and even beta) has been found and some suggestions have been given as to how this might occur through chain segregation mechanisms in the neat state. The literature suggests that further work needs to be done on the interaction of different chains that are covalently linked to the same molecule. Such studies will lead to a better understanding of the structure of lipid bilayers, membranes, lipoproteins, and lipid deposits.