The double salt tris(diisopropylammonium) tetrachloridoferrate(III) dichloride: Synthesis, crystal structure, and vibrational spectra

Tris(diisopropylammonium)tetrachloridoferrate(III) dichloride crystallizes in the monoclinic space group P2₁/c (a = 7.6685(2) ?, b = 17.6079(3) ?, c = 23.3217(4) ?, β = 91.396(2)°, V = 3148.1(1) ?³, Z = 4, T = 113 K) with three diisopropylammonium cations (dip), one tetrachloridoferrate(III) anion, and two chloride anions in the asymmetric unit. The dip cations and the chloride anions form hydrogen bonded one-dimensional polymers along [010]. The tetrachloridoferrate(III) anion, habituated in between these chains, is not involved in any hydrogen bonding. The structural characterization is supported by infrared and Raman spectroscopic data.     

Hydrate formation in the tetraethylammonium hydroxide-water system

A phase diagram of the tetraethylammonium hydroxide-water binary system was studied by differential thermal analysis. Seven crystal phases of tetraethylammonium hydroxide were found. Two of them are stable: tetrahydrate (T _m = 47.0°C), two phases of a compound with the hydration number 7.5 (T _m = −18.1 and −23.2°C); five are metastable phases: two polymorphs of pentahydrate (T _m = 39.4 and 0.9°C), hexahydrate (T _m = −70.1°C), and a compound with hydrate number 10–11 (T _m = −112°C).     

Influence of MgO (CaO) on the structure of silicate-phosphate glasses

Thermal and structural properties of model silicate-phosphate glasses containing the different amounts of the glass network modifiers, i.e. Mg²⁺ and Ca²⁺ were studied. To explain the changes of the parameters characterizing the glass transition effect (T_g, Δc_p) and the crystallization process (T_c, ΔH) depending on the cations modifiers additions, analysis of the bonds and chemical interactions of atoms in the structure of glasses was used. ³¹P MAS-NMR spectra of SiO₂–P₂O₅–MgO(CaO)–K₂O glasses show that the phosphate complexes are mono- and diphosphate. It has been found that increasing amounts of Mg²⁺ or Ca²⁺ cations in the structure of glasses causes the reduction of the degree of polymerization of the phosphate framework (Q¹→Q⁰). The influence of increasing of modifiers in the structure of silicate- phosphate glasses on the number of non-bridging oxygens per SiO₄ tetrahedron and density of glasses was presented.     

Eight-arm star polystyrene in methylcyclohexane: Cloud-point curves,critical lines,and coexisting densities and viscosities

We measured the cloud-point curves of eight-arm star polystyrene (sPS) in methylcyclohexane (MCH) for polymer samples of three total molecular masses [weight-average molecular weight (M_w) × 10⁻³ = 77, 215, or 268]. We found a downward shift of 5–15 K in the critical temperature (T_c) of the star polymer solutions with respect to linear polystyrene (PS) solutions of the same M_w. The shift in T_c became smaller as M_w increased. The critical volume fraction for eight-arm sPS in MCH was equal within experimental uncertainty (10–40%) to that of linear PS in MCH. For sPS of M_w = 77,000 in MCH, we studied the mass density (ρ) as a function of temperature (T). As for linear polymers in solution, the difference in ρ between coexisting phases (Δρ) could be described over t = (T_c − T)/T_c for 1.1 × 10⁻⁴ < t < 4.7 × 10⁻³ with the Ising value of the exponent β in the expression Δρ = B t^β. Both ρ(T) above T_c and the average value of ρ below T_c were linear functions of temperature; no singular corrections were observed. The measurements of the shear viscosity (η) near T_c for sPS (M_w = 74,000) in MCH indicated a strong critical anomaly in η, but the data were not precise enough for a quantitative analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 129–145, 2004     

Magnesium and Cadmium in Covalently‐Bonded Lonsdaleite Networks: Synthesis,Structure, and Bonding of AETMg2 and SrTCd2 (AE = Ca,Sr; T = Pd,Ag, Pt,Au)

The alkaline earth metal compounds AETMg₂ and AETCd₂ (AE = Ca, Sr; T = Pd, Ag, Pt, Au) were synthesized by induction‐melting (or in muffle furnaces) of the elements in sealed niobium ampoules. The new phases were characterized by powder X‐ray diffraction. The structures of SrPdMg₂ and SrPdCd₂ were investigated by X‐ray diffraction on single crystals: MgCuAl₂ type, Cmcm, a = 436.42(4), b = 1130.1(1), c = 820.54(7) pm, wR₂ = 0.0115, 511 F² values for SrPdMg₂ and a = 443.5(2), b = 1063.0(2), c = 810.2(2) pm, wR₂ = 0.0296, 386 F² values for SrPdCd₂ with 16 variables for each refinement. The magnesium and cadmium atoms build up [TMg₂] and [TCd₂] polyanionic networks, which leave cavities for the calcium and strontium atoms. The bonding variations within the polyanions, which are mainly influenced by the length of the b axis are discussed. Ab initio calculations of electronic structure, charge densities, and chemical bonding, characterize SrPdMg₂ with a larger cohesive energy than SrPdCd₂. This is illustrated by larger bonding Pd–Mg interactions, opposite to compensating Pd–Cd between bonding and antibonding states.     

Competition of Viscosity Correlation Equations in Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature

Shear viscosity deviations Δη have been investigated by using density (ρ) and kinematic viscosity (ν) measurements for isobutyric acid + water (IBA + W) mixtures over the entire range of mole fractions at atmospheric pressure and at two temperatures (301.15 and 315.15 K). This study extends the temperature range from the five other temperatures investigated in a previous work, 1.055 K≤(T−T _c )≤14.055 K, both far from and close to the critical temperature. This system exhibits very large positive values of Δη due to increased hydrogen bonding interactions and the correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The results were also fitted with the Redlich–Kister polynomial equations and the recently proposed Herráez correlation equation. Comparisons between the two models at different temperatures and number of parameters are discussed. We note that, in this system where the shear viscosity η as a function of mole fraction (x ₁) of IBA presents a maximum, experimental data are in agreement with the two correlation models when more than three parameters are employed, especially for temperatures far from the critical temperature.     

The Influence of Drawing in Hot Water on The Morphological Properties of Pet Films as Measured by DSC and Modulated DSC

PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition is studied by MDSC which allows to access the glass transition temperature T _g and the variations of ΔC _p=C _p1−C _pg (difference between thermal capacity in the liquid-like and glassy states at T=T _g). Variations of T _g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed with regard to the structure engaged in these materials. The increments of ΔC _p at T _g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’ of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of cobalt complex on thermal properties of poly(ethylene terephthalate)/polycarbonate blend

The effects of processing time and concentration of cobalt acetylacetonate III complex in poly(ethylene terephthalate)/polycarbonate reactive blending were investigated. The blend was prepared in an internal mixer at 270°C, 60 rpm, at different processing times (5–20 min) and catalyst concentration (0.00625–0.075 mass%). The reaction product was evaluated by differential scanning calorimetry (DSC), thermogravimetry (TG) and wide angle X-rays scattering (WAXS). In general, the DSC curves showed two glass transition temperatures (T _g’s) close to each homopolymer, independent of the processing time and complex’s concentration, suggesting the presence of two phases: one rich in PET and other one rich in PC. In all cases, melting temperature (T _m), cold crystallization temperature (T _cc) and crystallinity degree (X _c) were progressively reduced with blending conditions. The TG curves presented two decays. The first one represented the PET rich phase and the other one was related to the PC phase. The WAXS diffractograms showed that the Bragg’s angle and interplanar spacing of PET remaining practically unchanged.     

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear T _g-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher T _g of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at T_c = 60 ~ 110^° C {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} ; however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on T _max (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a T _c (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same T _c from different T _max, higher T _max tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher T _max are not necessarily packed with thicker lamellae.     

Broken symmetry solutions of the two-dimensional extended hubbard model and their instability conditions

Instabilities of the restricted Hartree–Fock (HF ) state of the two-dimensional extended Hubbard model under doping are studied with the linear response theory employing the linearized Bethe–Salpeter equation. Boundaries of the instabilities for the ordering vectors q = Q ≡ (π, π) and q = Q₀ ≡ (0, 0) are given in terms of the interaction strength parameters at various doping levels. With doping, dominant instabilities generally change from ones for q = Q to ones for q = Q₀. Broken symmetry phases obtained from the instabilities are also studied and classified using the group-theoretical technique. For q = Q, two more new phases are obtained in addition to the four nonmagnetic and five magnetic phases that have been already derived by one of the authors. For q = Q₀, three nonmagnetic and five magnetic phases are obtained. Deriving the explicit forms of the charge current and spin current operators in the HF approximation, charge current and spin current densities in the broken symmetry states are discussed in detail. © 1992 John Wiley & Sons, Inc.