Selected X-ray diffraction and differential scanning calorimetry investigations of the binary system K-palmitate/glycerol

Three mole fractions of the binary system K-palmitate/glycerol (KC₁₆/Gl) x_KC16 = 0.30, 0.37 and 0.50 have been investigated as a function of temperature by small- and wide-angle X-ray diffraction investigations and differential scanning calorimetry (DSC) measurements. The existence of a gel-like region, named G₁ in the preliminary binary phase diagram [4], could not be confirmed. Consequently, a corrected version of the phase diagram of the KC₁₆/Gl system is established. According to this corrected phase diagram at low K-palmitate concentrations, x_KC16 < 0.25, the transitions crystalline phase (C) ⇆ hexagonal phase, chains fluid (H_α) ⇆ isotropic, micellar phase (S) occur with rising temperature. At x_KC16 > 0.25 the transitions C ⇆ gel phase (G) ⇆ lamellar phase, chains fluid (L_α) were observed. X-ray diffraction and DSC measurements provided concordant results. Only differences in the phase transition temperatures from DSC curves obtained at rising and falling temperatures were observed. The phase transitions C ⇆ G, G ⇆ L_α and G ⇆ H_α correlate with a sharp shift in the d value of the first small-angle reflection. The occurrence of the G phase is accompanied by a distinct split of the first small-angle reflections. Simultaneously, the wide-angle reflections change and the peak intensity is reduced. Received: 14 April 1999 Accepted: 28 June 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     

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     

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     

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     

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     

Synthesis and mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers

Connecting two discotic mesogens via a spacer not only stabilizes the columnar mesophase but also leads to the formation of glass columnar phase, and therefore improves the physical properties of discotic liquid crystals as organic semiconductor. Here, we report the synthesis of eight diacetylene-bridged triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)4(OMe)O2C-C8H16-C≡≡ C-]2, 3(n), (n = 4-8), [C18H6(OC6H13)5O2C-C8H16-C≡≡ C-]2, 6 and [C18H6(OC6H13)5O-(CH2)m-C≡≡ C-]2, 8(m), (m = 1, 3) by Eglinto...     

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     

Recombination of tert-butyl radicals: the role of weak van der Waals interactions

A mechanism for the recombination of tert-butyl radicals is postulated to involve the loosely bonded intermediates tert-C₄H₉⋯tert-C₄H₉. Three processes contribute to the overall recombination rate constant: tert-C₄H₉+ tert-C₄H ⇆ tert-C₄H₉⋯tert-C₄H₉ characterized by the equilibrium constant K ₁ and tert-C₄H₉⋯tert-C₄H₉ → C₈H₁₈* characterized by the rate constant k ₂, k _rec,∞(T) ≈ K ₁ k ₂. This recombination rate constant exhibits a negative temperature dependence and is proportional to T ^−3/2. The agreement with experiment is very good. Received: 2 October 2000 / Accepted: 2 May 2002 / Published online: 7 August 2002     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

Subsolidus binary phase diagram of (n-CnH2n+1NH3)2ZnCl4 (n?=?14, 16, 18)

The thermotropic phase solid–solid transitions compound (n-C _n H_2n+1NH₃)₂ZnCl₄ (n = 14, 16, 18) were studied, and a series of their mixtures were prepared. These laminar materials contain bilayers sandwiched between metal halide layers. The low temperature crystal structures of the pure salts are characteristic of the piling of sandwiches in which a two-dimensional macro-anion ZnCl₄ ²⁻ is sandwiched between two alkylammonium layers. These layers become conformationally disordered in the high temperature phases. The subsolidus binary phase diagrams of (n-C₁₄H₂₉NH₃)₂ZnCl₄-(n-C₁₈H₃₇NH₃)₂ZnCl₄ and (n-C₁₆H₃₃NH₃)₂ZnCl₄-(n-C₁₈H₃₇NH₃)₂ZnCl₄ were established by differential thermal analysis and X-ray diffraction. In each phase diagram, an intermediate compound and two eutectoid invariants were observed. There are three noticeable solid solution ranges (α, β, γ) at the left boundary, right boundary, and middle of the phase diagram.     

The Thermal Dehydration of Magnesium Aluminum Pentafluoride Dihydrate: Crystal Structures of MgAlF5(H2O)2 and MgAlF5

Summary.  Small plate-like single crystals of MgAlF₅(H₂O)₂ have been obtained during hydrothermal treatment (270°C) of microcrystalline material prepared by precipitation of stoichiometric solutions of Al₂(SO₄)₃ ·  18H₂O and Mg(NO₃)₂ · 6H₂O with diluted hydrofluoric acid. The crystal structure of MgAlF₅(H₂O)₂ has been refined from single crystal data (Imma (# 74), Z = 4, a = 7.0637(7), b = 10.1308(10), c = 6.7745(7) ?, 398 structure factors, 33 parameters, R(F² > σ(F ²)) = 0.0245, wR(F² all) = 0.0525). Main features of the inverse weberite type structure are infinite chains of trans-bridged [AlF₆] octahedra which are connected via common fluorine atoms by isolated [MgF₄(H₂O)₂] octahedra. MgAlF₅(H₂O)₂ dehydrates at temperatures above 300°C to give MgAlF₅. XRPD analysis of this phase has revealed isotypism with FeAlF₅. The crystal structure of MgAlF₅ (Immm (# 71), Z = 2, a = 7.268(1), b = 6.123(2), c = 3.543(1) ?) is built of infinite chains of edge-sharing [MgF₆] octahedra and chains of corner-sharing [AlF₆] octahedra along [001]. Upon further heating to temperatures above 500°C, MgAlF₅ decomposes to MgF₂ and α − AlF₃. Received January 15, 2001. Accepted February 12, 2001     

Subsolidus phase diagram of binary system in the perovskite type layer compounds (<Emphasis Type="Italic">n</Emphasis>-C<Subscript>n</Subscript>H<Subscript>2n+1</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>MnCl<Subscript>4</Subscript>

The thermotropic phase transitions in the perovskite type layer compound (n-C₁₀H₂₁NH₃)₂MnCl₄ and (n-C₁₄H₂₉NH₃)₂MnCl₄ were synthesized and, at the same time, a series of their mixtures C₁₀Mn-C₁₄Mn were prepared. The experimental binary phase diagram of C₁₀Mn-C₁₄Mn was established by differential thermal analysis (DTA), IR and X-ray diffraction. In the phase diagram new material (n-C₁₀H₂₁NH₃)(n-C₁₄H₂₉NH₃)MnCl₄ and two eutectoid invariants were observed, two eutectic points temperatures are about 29.8 and 27.9°C. Contrasting other similar system, there are three noticeable solid solution ranges (α, β, γ) at the left and right boundary and middle of the phase diagram.     

The Thermal Dehydration of Magnesium Aluminum Pentafluoride Dihydrate: Crystal Structures of MgAlF5(H2O)2 and MgAlF5

 Small plate-like single crystals of MgAlF₅(H₂O)₂ have been obtained during hydrothermal treatment (270°C) of microcrystalline material prepared by precipitation of stoichiometric solutions of Al₂(SO₄)₃ ·  18H₂O and Mg(NO₃)₂ · 6H₂O with diluted hydrofluoric acid. The crystal structure of MgAlF₅(H₂O)₂ has been refined from single crystal data (Imma (# 74), Z = 4, a = 7.0637(7), b = 10.1308(10), c = 6.7745(7) ?, 398 structure factors, 33 parameters, R(F² > σ(F ²)) = 0.0245, wR(F² all) = 0.0525). Main features of the inverse weberite type structure are infinite chains of trans-bridged [AlF₆] octahedra which are connected via common fluorine atoms by isolated [MgF₄(H₂O)₂] octahedra. MgAlF₅(H₂O)₂ dehydrates at temperatures above 300°C to give MgAlF₅. XRPD analysis of this phase has revealed isotypism with FeAlF₅. The crystal structure of MgAlF₅ (Immm (# 71), Z = 2, a = 7.268(1), b = 6.123(2), c = 3.543(1) ?) is built of infinite chains of edge-sharing [MgF₆] octahedra and chains of corner-sharing [AlF₆] octahedra along [001]. Upon further heating to temperatures above 500°C, MgAlF₅ decomposes to MgF₂ and α − AlF₃.     

Complexation Studies of Pyridyl Sulfonamide Ligands for Sensing Zinc and Copper Ions

Ligand protonation and stepwise dissociation constants, formation constants and speciation of four pyridyl sulfonamide ligands (Congreeve et al., New J. Chem. 27:98–106, 2003) were assessed, using potentiometric and UV/Visible spectrophotometric pH titrations (in 80% MeOH − 20% H₂O). The suitability of these ligands as Cu(II) and Zn(II) sensors for physiological applications was assessed. Two ligands L¹ and L⁴ were p-toluenesulfonamide derivatives while L² and L³ were triflurosulfonamide derivatives. Additionally L³ and L⁴ were appended with α-methyl groups. The most stable complex was formed by L¹ with Cu(II) owing to the fact that this complex was square planar (log ₁₀  K ₁=12.15±0.004 and log ₁₀  β ₂=15.42±0.006). The rest of the complexes invariably formed distorted tetrahedron geometry and complexation was weaker. Speciation diagrams show the effect of ligand to metal concentration, revealing that the L² and L³ ligands are the most suitable for forming ML₂ complexes at physiological pH.     

Thermodynamic investigation of effect of salt concentrations on denatured α-Amylase adsorbed onto a moderately hydrophobic surface

The displacement adsorption enthalpies (ΔH) of denatured α-Amylase (by 1.8 mol L⁻¹ GuHCl) adsorbed onto a moderately hydrophobic surface (PEG-600, the end-group of polyethylene glycol) from solutions (x mol L⁻¹ (NH₄)₂SO₄, 0.05 mol L⁻¹ KH₂PO₄, pH 7.0) at 298 K are determined by microcalorimeter. Further, entropies (ΔS), Gibbs free energies (ΔG) and the fractions of ΔH, ΔS, and ΔG for net adsorption of protein and net desorption of water are calculated in combination with adsorption isotherms of α-Amylase based on the stoichiometric displacement theory for adsorption (SDT-A) and its thermodynamics. It is found that the displacement adsorptions of denatured α-Amylase onto PEG-600 surface are exothermic and enthalpy driven processes, and the processes of protein adsorption are accompanied with the hydration by which hydrogen bond form between the adsorbed protein molecules favor formation of β-sheet and β-turn structures. The Fourier transformation infrared spectroscopy (FTIR) analysis shows that the contents of ordered secondary structures of adsorbed α-Amylase increase with surface coverages and salt concentrations increment.     

The Observation of Strong Absorption of the Yttrium Lα Line in Sialon Ceramics

 β-sialon ceramics sintered with yttria additives have been studied with the use of an electron probe X-ray analysis (EPMA). Sialon ceramics were prepared from a carbothermally derived β-sialon powder and then sintered in a nitrogen atmosphere with yttria admixture. The above process was followed by annealing in flowing nitrogen. Scanning electron microscope (SEM) observations have shown that the sintered material contains a glassy phase (Y-Si-Al-O-N) on the grain boundaries. X-ray diffraction (XRD) after annealing in nitrogen revealed the presence of a considerable amount of yttrium aluminium garnet (YAG). The higher voltage of 30 kV was used in order to excite the yttrium K_α radiation (14.96 keV) at an appropriate overvoltage ratio because in some phases of the material, the disappearance of the yttrium L_α line has been observed during EPMA examination at an accelerating voltage of 15 kV in energy dispersive spectra (EDS). The intensity of the yttrium K_α line was sufficiently high, while the Y L_α line was not seen in the ED spectrum. Because the position of the yttrium L_α line (1.922 keV) is very close to the Si (K) absorption edge (1.84 keV), the strong absorption at this edge is probably responsible for the effect. This result should be considered as a serious warning in the case of EPMA (EDS) studies on compounds or mixtures suspected to contain both silicon and yttrium, because at electrons energies lower than 15 keV, the presence of yttrium in materials can go unnoticed. In wavelength dispersive spectra (WDS) obtained at 15 keV the intensity of the yttrium L_α line was also very low but measurable.     

Stability of complex of Na+ with 18-crown-6 in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Na⁺(aq)+HL⁺(nb)⇆NaL⁺(nb)+H⁺(aq) taking place in the two-phase water-nitrobenzene system (L=18-crown-6; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logK _ex (Na⁺,HL⁺)=0.1. Further, the stability constant of the 18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: logβ _nh(NaL⁺)=8.0.     

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     

Synthesis and characterization of mesoporous Mn–Ni oxides for supercapacitors

Mesoporous Mn–Ni oxides with the chemical compositions of Mn_1-x Ni _x O _δ (x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO₂, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn_1–x Ni _x O _δ was 42.8, 59.6, and 84.5 m² g⁻¹ for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge in 6 mol L⁻¹ KOH electrolyte. Specific capacitances of Mn_1-x Ni _x O _δ were 343, 528, and 411 F g⁻¹ at a scan rate of 2 mV s⁻¹ for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g⁻¹ with increasing scan rate to 100 mV s⁻¹, respectively. After 500 cycles at a current density of 1.24 A g⁻¹, the symmetrical Mn_1–x Ni _x O _δ capacitors delivered specific capacitances of 160, 250, and 132 F g⁻¹ for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn_0.8Ni_0.2O _δ material showed better supercapacitive performance, which was promising for supercapacitor applications.