Two novel phase transition materials based on 1-isopropyl-1,4-diazabicyclo[2.2.2]octan-1-ium

Two novel phase transition materials,[C₉H₂₀N₂] [Na(BF₄)₃] (1) and[C₉H₂₀N₂] [(PF₆)₂] (2), were synthesized based on 1-isopropyl-1,4-diazabicyclo[2.2.2]octan-1-ium with sodium tetrafluoroborate and hexafluorophosphoric acid, respectively. Differential scanning calorimetry measurements detected that 1 and 2 underwent reversible phase transitions, which were confirmed by dielectric measurements. Single crystal X-ray diffraction data suggested that compound 1 changed from a high temperature phase with a space group of P6₃ to a low temperature one with a space group of P2₁/c, and that compound 2 transformed from the space group of Pbca at room temperature to P2₁/c at low temperature. Formation of hydrogen bonds and distortion of 1,4-diazabicyclo[2.2.2]octane rings may drive the transitions.     

Hydrogen‐Bonded Polymer–Porphyrin Assemblies in Water: Supramolecular Structures for Light Energy Conversion

In this study, a new type of functional, self‐assembled nanostructure formed from porphyrins and polyamidoamine dendrimers based on hydrogen bonding in an aqueous solution is presented. As the aggregates formed are promising candidates for solar‐energy conversion, their photocatalytic activity is tested using the model reaction of methyl viologen reduction. The self‐assembled structures show significantly increased activity as compared to unassociated porphyrins. Details of interaction forces driving the supramolecular structure formation and regulating catalytic efficiency are fundamentally discussed.

     

Mapping Hydration Water around Alcohol Chains by THz Calorimetry

THz spectroscopy was used to probe changes that occur in the dynamics of the hydrogen bond network upon solvation of alcohol chains. The THz spectra can be decomposed into the spectrum of bulk water, tetrahedral hydration water, and more disordered (or interstitial) hydration water. The tetrahedrally ordered hydration water exhibits a band at 195 cm⁻¹ and is localized around the hydrophobic moiety of the alcohol. The interstitial component yields a band at 164 cm⁻¹ which is associated with hydration water in the first hydration shell. These temperature‐dependent changes in the low‐frequency spectrum of solvated alcohol chains can be correlated with changes of heat capacity, entropy, and free energy upon solvation. Surprisingly, not the tetrahedrally ordered component but the interstitial hydration water is found to be mainly responsible for the temperature‐dependent change in ΔC_p and ΔG. The solute‐specific offset in free energy is attributed to void formation and scales linearly with the chain length.     

Synthesis,structural study and thermal behaviour of a new compound: trirubidium bis(hydrogen sulphate) dihydrogen arsenate Rb3(HSO4)2.5(H2AsO4)0.5

Mixed crystals Rb₃(HSO₄)_2.5(H₂AsO₄)_0.5 have been prepared by slow evaporation from aqueous solution at room temperature. The crystals were characterized by X-ray single analysis, which revealed that Rb₃(HSO₄)_2.5(H₂AsO₄)_0.5 crystallizes in the space group P with lattice parameters: a = 7.471(3) Å; b = 7.636(1) Å; c = 12.193(2) Å; α = 71.91(1)°; β = 73.04(6)° and γ = 88.77(2)°. In this structure, the ordered S(1)O₄ and the disordered S(3)/AsO₄ tetrahedra are connected by O–H..O hydrogen bonds, to a zigzag chains running in the b-direction. These chains are, in turn, bonded to one another by disordered hydrogen bridges O–H..H–O, to give a planar structure, with hydrogen-bonded sheets, laying parallel to (1 0 0). Each disordered tetrahedron is linked to a tetrahedron neighbouring S(2)O₄ by ordered hydrogen bonds. Broader peaks in IR spectrum of the title material support the assumption of disordered structure. Thermal analysis of the superprotonic transition in Rb₃(HSO₄)_2.5(H₂AsO₄)_0.5 showed that the transformation to the high-temperature phase occurs by one-step process at 404 K. Thermal decomposition of this compound takes place at much higher temperatures, with an onset of approximately 473 K.     

The determination of the glass transition temperature by thermally stimulated depolarization currents. Comparison with the performance of other techniques

Several experimental techniques are currently used for the determination of the glass transition temperature, T_g. Thermally stimulated depolarization currents (TSDC) is a thermal analysis technique whose experimental results display a very clean glass transition signature and that, nevertheless, is seldom used as a technique for T_g determination. In the present work we explain how to get the glass transition temperature from TSDC data, and we compare the values obtained for a vast number of glass forming systems (with T_gs in a wide range between ?145 and +180 °C and fragilities between m = 15 and m = 100), with the values obtained by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). We conclude that the T_g determination by TSDC is direct, accurate and reproducible and that the obtained values correlate very well with those obtained by DSC and DRS. This general survey thus suggests TSDC as a valuable alternative technique for determining T_g.     

Homopolar bonds in Se-rich Ge-As-Se chalcogenide glasses

We have prepared three groups of Ge–As–Se glasses in which the Se content is 5.5 mol%, 10 mol%, and 20 mol%rich, respectively. We explored the possibility of suppressing the formation of the Ge–Ge and As–As homopolar bonds in the glasses. Thermal kinetics analysis indicated that the 5.5 mol% Se-rich Ge_(11.5)As_(24)Se_(64.5) glass exhibits the minimum fragility and thus is most stable against structural relaxation. Analysis of the Raman spectra of the glasses indicated that the Ge–Ge and As–As homopolar bonds could be almost completely suppressed in 20 mol% Se-rich Ge_(15)As_(14)Se_(71) glass.     

Tempering effects on three martensitic carbon steels studied by mechanical spectroscopy

Tempering effects have been studied in three martensitic carbon steels by mechanical spectroscopy. The mechanical-loss spectra present a relaxation peak similar to the Snoek-Köster peak in ferrite. The peak amplitude decreases upon tempering, indicating a decrease of the dislocation density. Transition carbides start to precipitate at 380 K in all the three grades. This tends to decrease the mechanical loss and to increase the modulus. Retained austenite decomposes around 520 K in two of the grades. In the third grade, the presence of Si delays this decomposition to 670 K. The decomposition of retained austenite leads to a sudden decrease of amplitude of the relaxation peak and a modulus anomaly. Both these effects can be attributed to a decrease of the dislocation density in martensite, probably associated with the depletion of carbon atoms in the dislocation core. At low frequency, a mechanical-loss peak associated with the decomposition of retained austenite is visible.     

Effect of iron doping on the characterization and transport properties of calcium phosphate glassy semiconductors

X-ray diffraction (XRD), differential scanning calorimeter (DSC), density (d) and dc conductivity (σ) of the glasses in Fe₂O₃-CaO-P₂O₅ system were reported. The dc conductivity in the temperature range 303-453 K was measured. The overall features of these XRD curves confirm the amorphous nature of the present samples. The density of glasses increases from 2.750 to 2.892 g/cm³ with increasing Fe₂O₃ content as a result of a strengthening of cross-linking within glass network. The glass temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The glasses had conductivities ranging from 10⁻⁹ to 10⁻⁵ Sm⁻¹ at temperatures from 303 to 453 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

三元溶液共晶DSC实验研究

抑制共晶产生对低温保存非常重要。本文利用差示扫描量热法研究了加低温保护剂(DMSO、乙二醇、 1,2丙二醇、甘油和1,3丁二醇)的NaCl水溶液的共晶行为。得到以5％、10％、15％NaCl水溶液为母液的五种保护剂溶液热流曲线图。研究发现,溶液共晶是过冷、随机过程。低温保护剂有抑制NaCl水溶液共晶的作用。低温保护剂浓度越高, 共晶焓越小,对共晶的抑制作用越大。不同种类保护剂的抑制共晶的能力从强到弱依次是甘油、乙二醇、 DMSO、 1,2 丙二醇和1,3丁二醇。升温过程中,溶液发生共晶反玻璃化现象和玻璃化现象。     

Fluoride glasses in the InF3-GaF3-YF3-PbF2-CaF2-ZnF2 system

New glasses have been synthesized in a multicomponent system based on indium fluoride. Samples of a few mm in thickness were obtained. They are transparent and homogeneous. Main physical properties such as density, characteristic temperatures, density, thermal expansion and refractive index have been measured. The evolution versus composition is reported for samples with the formula: (35−x) InF₃-xGaF₃-10YF₃-25PbF₂-15CaF₂-15ZnF₂. T_g lies between 260 and 296 °C while melting starts around 480 °C. Glass samples are stable at room temperature. By comparison with other standard fluoride glasses, they exhibit higher refractive index and density.