Time and poling history dependent energy storage and discharge behaviors in poly(vinylidene fluoride-<Emphasis Type="Italic">co</Emphasis>-hexafluoropropylene) random copolymers

 We studied cycle time (0.01–10 s with triangular input waves) and poling history (continuous versus fresh poling) dependent electric energy storage and discharge behaviors in poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] films using the electric displacement ― the electric field (D-E) hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly (< 5 ms for each process), while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used.     

离子液体[Bmim]BF4中单分散Ru纳米粒子的制备及选择加氢性能

采用化学还原法在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([BMim]BF₄)中制备了单分散纳米金属Ru粒子。采用X射线衍射(XRD)、透射电镜(TEM)、傅里叶红外光谱(FTTR)及热重(TG)对所制备样品的形貌和结构进行了表征。XRD表征结果显示：在[BMim]BF₄中制备的Ru具有六方紧密堆积结构,无氧化物峰出现;TEM结果显示：采用正滴法制备的Ru纳米粒子为球形颗粒,呈现良好的单分散状态,粒径分布窄,为2~5 nm,而采用反滴法制备的Ru纳米粒子则发生了严重的团聚,团聚体粒径大于10 nm;FTIR表征表明：Ru纳米粒子表面存在[BMim]BF₄液体层,分析二者之间存在较强的物理吸附作用,[BMim]BF₄在Ru纳米粒子的制备中起到了修饰剂和保护剂的双重作用,这一推论通过TG分析得到了进一步验证。将分散于[BMim]BF₄的Ru纳米粒子作为催化剂应用于苯选择加氢反应,结果分析表明：Ru-离子液体-苯反应体系中,苯转化率仅有0.3%;Ru-离子液体-苯-水反应体系中加氢活性较高,但环己烯选择性较低,在一定条件下,加氢30 min,苯转化率为27.3%,环己烯选择性仅为14.5%。     

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

Microcalorimetric Studies on the CMC and Thermodynamic Functions of a Nonionic Surfactant (Tween80) in DMF/Long-Chain Alcohol Systems from <Emphasis Type="Italic">T</Emphasis>=298.15 to <Emphasis Type="Italic">T</Emphasis>=313.15 K

The power-time curves of the micelle formation process were determined for the nonionic surfactant Tween80/nonaqueous solvent (DMF)/long-chain alcohol (n-heptanol, n-octanol, n-nonanol, and n-decanol) systems by titration microcalorimetry at temperatures of (298.15, 303.15, 308.15, and 313.15) K. From the power-time curves, the CMC and DH_m^\uptheta\Delta H_{\mathrm{m}}^{\uptheta} values were obtained. The corresponding values of DG_m^\uptheta\Delta G_{\mathrm{m}}^{\uptheta} and DS_m^\uptheta\Delta S_{\mathrm{m}}^{\uptheta} were also calculated. The relationships of the CMC with the carbon number of the alcohol, the concentration of alcohol, and the temperature, along with the thermodynamic functions, are discussed.     

Effect of Solvents and pH on <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

The spectral characteristics of 2,4-dihydroxyazobenzene (DHAB, sudan orange G) and 4-hydroxyazobenzene (HAB) have been studied in various solvents, different hydrogen ion and β-cyclodextrin (β-CD) concentrations, and are compared with azobenzene (AB). The inclusion complexes of the above molecules with β-CD were analyzed by UV-vis spectrometry, flourometry, FT-IR, ¹H NMR, SEM and DFT methods. The solvent study shows that only the azo form is present in DHAB and HAB molecules. The unusually large red shift observed in acidic solutions indicates both molecules exhibit azo-hydrazo tautomerization. In the β-CD solutions, the increase in fluorescence intensity and large bathochromic shift in the S₁ state indicates that DHAB and HAB form 2:2 inclusion complexes, whereas AB forms a 1:1 inclusion complex.     

Study on the Synergism Effect of Lomefloxacin and Ofloxacin for Bovine Serum Albumin in Solution by Spectroscopic Techniques

Both lomefloxacin (LOM) and ofloxacin (OFL) have a powerful ability to quench the fluorescence of bovine serum albumin (BSA). The fluorescence quenching action is much stronger when the two drugs coexist. The synergism between LOM and OFL was studied using fluorescence and ultraviolet spectroscopy under imitated physiological conditions. The results show that static quenching and non-radiation energy transfer are the main reasons for the fluorescence quenching. The synergism results in both the reduction of the binding stability between drugs and BSA and an increase of the free drug concentration, which will increase the efficacy of drugs. The thermodynamic parameters at different temperatures were calculated and the binding distances r between the drugs and BSA were obtained based on Försters theory of non-radiation energy transfer. The synchronous fluorescence spectra indicated that the effect of synergism affected the conformation of BSA.     

A General Formulation Encompassing the Effects of Salts and Micelles (Direct and Reverse) on Ionic Reactions

Given the common behavior of ionic reactions in micellar and salt solutions and in microemulsions, a general approach has been developed for the interpretation of kinetic results in these media. This approach takes as a starting point the Brønsted equation. It has been checked by employing kinetic results for cation/cation \(([\mathrm{Ru}(\mathrm{NH}_{3})_{5}\mathrm{py}^{2+}] + [\mathrm{Co}(\mathrm{NH}_{3})_{4}\mathrm{pzCO}_{2}^{2+}])\), anion/anion \((\mathrm{I}^{-}+ \mathrm{IrCl}_{6}^{2-})\) and cation/anion \(([\mathrm{Ru}(\mathrm{NH}_{3})_{5}\mathrm{py}^{2+}] + \mathrm{S}_{2}\mathrm{O}_{8}^{2-})\) reactions. The approach can be easily generalized to cases in which more than two pseudophases (or more than one receptor) are present in the reactive system, as well as cases in which the reaction can follow more than two reaction paths. The approach is consistent with (but more general than) the Pseudophase and related models, such as the Pseudophase Ion Exchange Model.     

Synthesis Characterization and Viscosity Studies of Homopolymer of Methyl Methacrylate and Copolymer of Methyl Methacrylate and Styrene

A homopolymer of methyl methacrylate (MMA) and its copolymer with styrene at different compositions were synthesized and characterized. Viscosity measurements of the synthesized homopolymer and the copolymers in toluene solutions were performed at 313 K. Different equations were used to calculate the intrinsic viscosity, viscometric constants values, and molecular weight of the synthesized polymers. The values of intrinsic viscosity and viscosity average molecular weight obtained by the two methods (single point determination and graphical extrapolation) were compared in order to verify the validity of the single point determination for the polymers. Viscometric properties derived included the specific viscosity (it determines the contribution of the solute to the viscosity of the solution), the reduced viscosity (that provides a measure of the polymer capacity for increasing the solution viscosity), and the intrinsic viscosity.     

Coordination characteristics of trivalent lanthanides and actinides in molten hydrate salts of Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> and CaCl<Subscript>2</Subscript>

Distribution behavior of Ce(III), Am(III), and Cm(III) between tri-n-butyl phosphate solution and molten calcium nitrate hydrate Ca(NO₃)₂·RH₂O or molten calcium chloride hydrate CaCl₂·RH₂O was studied radiochemically. In Ca(NO₃)₂·RH₂O systems, maximum separation factors of Ce and Cm to Am were observed to be 12 (Ce/Am) and 1.7 (Cm/Am). The distribution ratios of these elements increased with the decrease of water activity in the hydrates, and the extractabilities at the water deficient region was less sensitive compared to those at the water abundant region. This trend was similar to the coordination circumstance change observed in electronic absorption spectra of Nd(III) in the hydrates.     

Comparison of fluorescence-enhancing reagents and optimization of laser fluorimetric technique for the determination of dissolved uranium

Results from tests aimed at optimizing an instrumental procedure for the direct and fast determination of uranium in solution by laser fluorescence are presented. A comparison of sample fluorescence measured using different fluorescence enhancing reagents was performed: sodium pyrophosphate, orthophosphoric acid, sulphuric acid and a commercially available fluorescence enhancer were tested for the determination of uranium. From the experimental results, 0.01 M Na₄P₂O₇·10H₂O showed the best performance. Effects of reagent pH, different matrices, different concentrations of dissolved Th, and sample volume were investigated. Applications of the improved procedure for the determination of uranium in samples arising from UO₂-based high level nuclear waste dissolution studies are described.