Structural and calorimetric investigations on nonaqueous liquid crystals and gel phases in the binary system K-stearate/glycerol

The K-stearate/glycerol (KC₁₈/Gl) binary system was studied at mole fractions of stearate of x _KC18 = 0.10, 0.25, 0.30 and 0.50. Small- and wide-angle X-ray diffraction (XRD) measurements were combined with differential scanning calorimetry (DSC) measurements at different temperatures. The investigations were intended to verify the previously published phase diagram and were targeted at the confirmation of the gel-like (G₁) phase and the isotropic (I) phase. The XRD and DSC measurements lead to the conclusion that the G₁ phase as well as the I phase, the existence of which had been proposed from texture observations, do in fact not exist. Consequently, a correction of the preliminary phase diagram is given. This corrected phase diagram reveals the crystalline phase (C) ⇆ gel phase (G) ⇆ hexagonal phase (H_α) ⇆ isotropic, micellar phase phase transitions for low KC₁₈ concentrations of x _KC18 = 0.15–0.3 and the C ⇆ G ⇆ lamellar phase (L_α) phase transitions for concentrations about or higher than x _KC18 = 0.35. The C, G, L_α and H_α phases have been further characterized by structural parameters (characteristic d values) as a function of temperature. The phase transitions C ⇆ G, G ⇆ L_α and G ⇆ H_α correlate with sharp shifts in the d value of the first small-angle reflections. Received: 20 April 1999 Accepted: 28 July 1999     

Structural and calorimetric investigations on nonaqueous liquid crystals and gel phases in the binary system K-behenate/glycerol

Two mixtures of the binary system K-behenate/glycerol, x _KC22 = 0.30 and 0.50 (x = mole fraction), have been investigated as a function of temperature using small- and wide-angle X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The binary phase diagram based on texture observations using polarizing optical microscopy was confirmed. XRD and DSC measurements provided concordant results with respect to the range of the phase regions in the phase diagram. Only differences between the DSC curves for rising and falling temperatures were detected. The recorded XRD and DSC data of the liquid crystals and gel phases observed are also in agreement with previously reported investigations on K-soap/glycerol. The C ⇆ G and G ⇆ L_α phase transitions correlate with a sharp shift in the d value of the first small-angle reflection. The G phase is characterized by a split of the first small-angle reflections. Also, the position and shape of the wide-angle reflections change and the peak intensity is reduced. Received: 5 July 1999 Accepted in revised form: 27 July 1999     

Selected X-ray diffraction and differential scanning calorimetry measurements on nonaqueous liquid crystals and gel phases in the K-myristinate/glycerol binary system

Samples from the three selected concentrations x _KC14 = 0.25,0.37, and 0.50 of the K-myristinate/glycerol (KC₁₄/Gl) binary system have been investigated by means of small- and wide-angle X-ray diffraction measurements as well as differential scanning calorimetry (DSC) measurements as a function of temperature. The results are – The G₁ gel phase, contained in the preliminary phase diagram according to Dörfler and Senst [(1993) Colloid Polym Sci 271: 173], is nonexistent. – The same applies of the isotropic phase in the preliminary phase diagram according to Dörfler and Senst. Initially an isotropic or a cubic phase was assumed based on polarized microscopy texture observations. X-ray diffraction and DSC measurements provided no indication for their existence. – Due to the nonexistence of the G₁ and isotropic phases the preliminary phase diagram of the KC₁₄/Gl binary system had to be corrected. The region of the lamellar phase extends over a wider region. – X-ray diffraction and DSC measurements provided concordant results, which were further confirmed by electron microscopic investigation. Differences in phase-transition points from DSC data obtained for rising and falling temperatures have been observed. – The crystalline-to-gel phase transition correlates with a sharp shift in the d value of the first small-angle reflex. – The gel phase is accompanied by a distinct splitting of the first small-angle reflexes. The wide-angle reflexes show rearrangement and reduced intensity. – Similar to the crystalline-to-gel phase transition, the gel-to-lamellar phase transition is accompanied by a sharp change in the d values.     

Influence of the chain length of K-soaps on the phase diagram and structural parameters of nonaqueous liquid crystals and the gel phase in K-soap/glycerol binary systems

 Analogously to the aqueous K-soap/water systems already examined, the five glycerol · (Gl)-containing systems KC _n /Gl (n = 12, 14, 16, 18, 22) also built up hexagonal (H_α), lamellar (L_α), isotropic micellar (S), gel-like (G) and crystalline phases (C). These phases were identified by texture observations with a polarizing microscope, by differential scanning calorimetry measurements and by X-ray diffraction investigations. The appertaining phase regions were plotted in the binary phase diagram. Binary Gl-containing K-soap systems have the following properties. The H_α phase is built up at low soap concentration. The L_α phase is formed at high soap concentrations. The temperature of the phase transition H_α ⇆ S runs through a maximum. Increasing the chain lengths of the soaps shifts the formation of the H_α phase to lower soap concentration. A strong correlation between the chain length of K-soaps and the d values of L_α, H_α, G and C phases is found. Based on the comparison of the X-ray diffractograms of the G phase a structural model is proposed. The G phase consists of two groups of domains with two different dimensions. Received: 9 August 1999/Accepted in revised form: 20 September 1999     

Methodical developments for X-ray diffraction measurements and data analysis on lyotropic liquid crystals applied to K-soap/glycerol systems

 X-ray diffraction (XRD) data acquisition and processing software measurements on long-spacing binary systems, including adapted noise reduction algorithms, has been developed. The computation of XRD patterns has been summarized and the origin of the distinct patterns of long-spacing compounds has been illustrated with the aid of such simulations. This also provided the possibility to evaluate the retrievable amount of information used for graphical or numerical indexing programs. Numerical indexing programs were applied and limits of indexing method have been discussed. Differential scanning calorimetry (DSC) measurements and temperature-dependent XRD measurements have been carried out for the concentrations x _{KC 12} = 0.50 and 0.30 of the K-laurate/glycerol system. The analysis of the small- and wide-angle diffractograms in the various phase regions of the binary system as well as the DSC measurements provided the following results: – The creation of the lamellar phase extends over a temperature range of ΔT≈ 20 K at a concentration of x _{KC 12} = 0.50. The lamellas show a reduced degree of order. – The crystalline-to-gel phase transition is accompanied by a leap in the d values corresponding to the small-angle reflexes. Also a distinct splitting of the small-angle reflexes is observed within the gel phase. Simultaneously a rearrangement and intensity decay of the wide-angle reflexes occurs. Since some wide-angle reflexes are still present, the structure can be considered to have a partially reduced three-dimensional order. – During the creation of lamellar phases the d value decreases sharply with rising temperature. This decrease of d can be interpreted as a further decay of molecular order in the hydrocarbon chains of the K-laurate within the bilayers. – The XRD measurements correlate with the DSC data. According to our measurements a revision of the phase diagram with respect to the actual extension of the gel-phase region was necessary. Received: 3 March 1999 Accepted in revised form: 29 March 1999     

Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants

We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C _x C _y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical L_α phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out. Received: 7 April 1999 Accepted in revised form: 30 April 1999     

Investigation of molecular order and phase transitions of smectic poly(ester imide)s by means of small-angle X-ray scattering

The molecular order and phase transitions of two smectic poly(ester imide)s based on aminobenzoic acid trimellitimide (PEI 1) or aminocinnamic acid trimellitimide (PEI 2) and α,ω-dihydroxydodecane were investigated by X-ray scattering. During cooling, the polymers pass through monotropic smectic liquid-crystalline (LC) phases (S_A, S_C), which transform into higher-ordered smectic-crystalline phases (S_E, S_H). The smectic layer structure of about 3 nm gives rise to a sharp reflection at 2θ ≅ 3°. Peak shape analysis and analysis of the interface distribution function revealed long-range longitudinal correlation among the mesogens in the LC phase but short-range lateral correlation. The development of a broad reflection in the small-angle X-ray scattering (SAXS, 2θ < 1°) indicates the formation of a lamellar two-phase system. The long-period changes reversibly between 10 and 30 nm with increasing temperature. The crystalline lamellae comprise a number of smectic-crystalline layers with packed mesogens, while the noncrystalline interlamellar regions keep their smectic-LC order. In the metastable S_B phase, formed during annealing of quenched PEI 1, the diffuse SAXS indicates a random distribution of small, probably fringed, crystals with hexagonal-packed mesogens. In the lamellar S_E and S_H phases, tie molecules play an important role, but chain folding cannot be excluded. Received: 16 July 1999/Accepted: 28 April 2000     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

The phase diagram of CsNO<Subscript>3</Subscript>–RbNO<Subscript>3</Subscript>

The phase transitions of RbNO₃ and the binary phase diagram of (Cs,Rb)NO₃ were investigated at atmospheric pressure, using simultaneous direct and differential thermal analysis, μDTA and DSC techniques. A fourth phase transition of RbNO₃ has been observed at temperature near the melting point. The phase diagram of this system is characterised by a eutectic, two eutectoid and an azeotropic-like invariants. Three limited solid solutions and two continuous solid solutions have been detected at low temperature.     

Analysis of magnetic and structural phase transition behaviors of La1−xSrxCrO3 for preparation of phase diagram

The phase transition behavior of perovskite-type compounds, La_1−xSr_xCrO₃, was investigated by differential scanning calorimetry (DSC), dilatometry, dc magnetic susceptibility measurement and X-ray diffraction analysis. Both second-order magnetic phase transition from antiferromagnetic to paramagnetic and first-order structural phase transition from orthorhombic to rhombohedral were observed in the DSC or dilatometric curve of every specimen. The temperatures of both these magnetic and structural phase transitions decreased linearly with an increase in Sr content. The structural phase transition temperature of La_1−xSr_xCrO₃ with x less than 0.11 is higher than the magnetic phase transition temperature; however, a larger decrease in structural phase transition temperature than in magnetic phase transition temperature was observed with an increase in Sr content, resulting in a structural phase transition temperature lower than the magnetic phase transition temperature for La_1−xSr_xCrO₃ with x of more than 0.12. It was also observed that the heat of absorption of the structural phase transition decreased with an increase in x. In the dependence of dc magnetic susceptibility on temperature, variations by not only magnetic but also structural phase transitions were observed. It was also revealed that thermal expansion coefficient is affected not only by structural phase transition but also magnetic phase transition. Magnetic and structural phase diagram of La_1−xSr_xCrO₃, suggesting the existence of two Sr contents and temperatures at which triple phases coexist, was proposed.     

Changes of mechanical properties in cold-crystallized syndiotactic polypropylene during aging

Many semicrystalline polymers undergo a process of aging when they are stored at temperatures higher than their glass-transition temperature (T _g). Syndiotactic polypropylene was quenched from the melt to −40 °C, crystallized from the glassy state at 20 or 40 °C and stored at the respective temperature for different aging times up to 7200 h. A significant increase in the tensile modulus and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry (DSC) scans of aged material showed an endothermic annealing peak 15–30 °C above the previous aging temperature, the maximum temperature and enthalpic content of which increased with aging time. The position and the shape of the melting peak were not affected by aging. Scans of the storage modulus obtained from dynamic mechanical analyser measurements indicated a softening process starting at about 20 °C above the aging temperature and correlating with the annealing peak detected by DSC. Density measurements and wide-angle X-ray scattering investigations revealed that neither the crystallinity increased significantly nor did the crystal structure change. So the observed property changes induced by aging are attributed to microstructural changes within the amorphous phase. Furthermore, it could be shown by annealing experiments carried out at 60 °C, that aging above T _g is, analogous to aging below T _g (physical aging), a thermoreversible process. Received: 18 September 2000 Accepted: 2 January 2001     

Revised Phase Diagram of the System NaF–NaBF4

Summary. The phase diagram of the binary system NaF–NaBF₄ was determined using the thermal analysis method. Subsequent coupled analysis of the thermodynamic and phase diagram data was carried out to calculate the thermodynamically consistent phase diagram. The system NaF–NaBF₄ forms a simple eutectic phase diagram with the calculated coordinates of the eutectic point: 8.1 mol% NaF, 91.9 mol% NaBF₄, and 385.7°C. The probable inaccuracy in the calculated binary phase diagram is 9°C.     

A temperature study on critical micellization concentration (CMC), solubility, and degree of counterion binding of α-sulfonatomyristic acid methyl ester in water by electroconductivity measurements

 For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around 0 °C. The changes in the Gibbs energy, ΔG ⁰ _m, enthalpy, ΔH ⁰ _m, and entropy, ΔS ⁰ _m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation. Received: 28 August 1996 Accepted: 5 November 1996     

Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems

The influence of chain length differences of cephalines and the influence of the head group methylation on the miscibility behavior of N-methylated phosphatidylethanolamine (PE) mixtures in aqueous dispersions were tested. Nine different phase diagrams were studied by means of differential scanning calorimetry. The phase diagrams of the five pseudobinary cephaline/cephaline/water systems (fatty acid chain length: C _n , n = 12–18) showed that in the high temperature L_α phase all the homologous cephalines were completely miscible. In the low-temperature phase a distinct succession of the phase diagram types was observed according to increasing chain length differences of the PEs: complete miscibilty (C₁₂/C₁₄; C₁₄/C₁₆), peritectic mixing behavior (C₁₂/C₁₆; C₁₄/C₁₈), eutectic mixing behavior (C₁₂/C₁₈). Furthermore four phase diagrams of pseudobinary phospholipid systems consisting of N-methylated PEs with different numbers of methyl groups and a constant length of fatty acid chains were investigated and compared. These four phase diagrams showed phase separations in the low-temperatures phase (gel phase). The width and the concentration range of the miscibility gaps changed systematically with increasing degree of methylation of the head group of the mixing components and are connected with different possibilities of PEs to form hydrogen bridges between the mixture components. Received: 26 August 1999/Accepted: 30 August 1999     

New doped Li-M-Mn-O (M = Al, Fe, Ni) spinels as cathodes for rechargeable 3 V lithium batteries

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M _x Mn_{1− x} CO₃ (M = Fe, Ni; x = 0.08−0.15) or Al _x Mn_{1− x} (CO₃) (OH) _y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure. Received: 25 November 1997 / Accepted: 28 January 1998     

Phase Relations in the Ni–Mn–Ga Ternary System and Aging Effect on Shape Memory Properties of Ferromagnetic Ni<Subscript>2</Subscript>MnGa Sputtered Films

Summary. Isothermal sections of the Ni–Mn–Ga ternary phase diagram at 1073 and 1273 K were investigated over a wide range of alloy compositions. The range of the β-Ni₂MnGa phase, its equilibria with the γ-(Mn, Ni), α′-Ni₃Ga, and γ-Ni₃Ga₂ phases, and the liquidus and solidus lines were determined experimentally. The aging effect on the shape memory effect (SME) of Ni₂MnGa sputtered films was also investigated. The two-way SME of the constraint-aged films was confirmed by the temperature change.     

Thermochemistry of the binary system nitrocellulose+N-nitrodiethanolamine dinitrate

The melting and mixing enthalpy of the binary system nitrocellulose and N-nitrodiethanolamine dinitrate (DINA) was determined by DSC. The mixing enthalpy H _max^M = 1.95 kJ mol⁻¹ had maximum at mass fraction x _wDINA=0.46. The influence of samples storing on glass and endothermic transitions were studied. The temperature range of glass transition broadened with x _wDINA what proved the increase of samples heterogeneity. For x _wDINA≤0.750 no influence of samples storing on the phase changes was observed. The heat capacity change decreased and temperature range of glass transition increased for x _wDINA≤0.500 what indicated the reduction of glass phase fraction in studied samples.     

Phase Relations in the Ni–Mn–Ga Ternary System and Aging Effect on Shape Memory Properties of Ferromagnetic Ni2MnGa Sputtered Films

Isothermal sections of the Ni–Mn–Ga ternary phase diagram at 1073 and 1273 K were investigated over a wide range of alloy compositions. The range of the β-Ni₂MnGa phase, its equilibria with the γ-(Mn, Ni), α′-Ni₃Ga, and γ-Ni₃Ga₂ phases, and the liquidus and solidus lines were determined experimentally. The aging effect on the shape memory effect (SME) of Ni₂MnGa sputtered films was also investigated. The two-way SME of the constraint-aged films was confirmed by the temperature change.     

Cell membrane chromatography competitive binding analysis for characterization of α<Subscript>1A</Subscript> adrenoreceptor binding interactions

A new high α_1A adrenoreceptor (α_1AAR) expression cell membrane chromatography (CMC) method was developed for characterization of α_1AAR binding interactions. HEK293 α_1A cell line, which expresses stably high levels of α_1AAR, was used to prepare the stationary phase in the CMC model. The HEK293 α_1A/CMC-offline-HPLC system was applied to specifically recognize the ligands which interact with the α_1AAR, and the dissociation equilibrium constants (K _D) obtained from the model were (1.87 ± 0.13) × 10⁻⁶ M for tamsulosin, (2.86 ± 0.20) × 10⁻⁶ M for 5-methylurapidil, (3.01 ± 0.19) × 10⁻⁶ M for doxazosin, (3.44 ± 0.19) × 10⁻⁶ M for terazosin, (3.50 ± 0.21) × 10⁻⁶ M for alfuzosin, and (7.57 ± 0.31) × 10⁻⁶ M for phentolamine, respectively. The competitive binding study between tamsulosin and terazosin indicated that the two drugs interacted at the common binding site of α_1AAR. However, that was not the case between tamsulosin and oxymetazoline. The results had a positive correlation with those from radioligand binding assay and indicated that the CMC method combined modified competitive binding could be a quick and efficient way for characterizing the drug–receptor interactions.     

Galvanic synthesis of copper selenides Cu2 − x Se and CuSe in alkaline sodium selenosulfate aqueous solution

Spherical copper selenide nanoparticles (NPs) were prepared by a simple reaction of sodium selenosulfate with metal copper at room temperature in alkaline Na₂SeSO₃ aqueous solution. It is a galvanic process that operates on a coupled anodic copper oxidation and selenosulfate reduction. 1-Thioglycerol is found to catalyze this reaction. With gold and graphite as the positive electrodes, nanocrystallites of nonstoichiometric copper selenide (Cu_2 − x Se) and stoichiometric copper selenides (CuSe) were produced, respectively. The XRD study shows that the produced CuSe and Cu_2 − x Se are in the pure hexagonal phase and clausthalite phase, respectively. Transmission electron microscopy images show that the diameters of the produced CuSe and Cu_2 − x Se NPs are in the range of 10∼20 and 5∼15 nm, respectively.