Theory of profiles of hydrogen stretching infrared bands of hydrogen-bonded solids. Multi-Fermi resonance effects and strong coupling between the high-frequency hydrogen stretching vibration and low-frequency phonons

A theory is developed to describe the profiles of hydrogen stretching infrared bands of hydrogen-bonded solids taking into account the anharmonic coupling between the high-frequency stretching vibration, ν(XH), and low-frequency lattice phonons, Ω_i, as well as multi-Fermi resonances between states involving the ν(XH) stretching and overtones or combinations of some internal modes. The theory has been constructed in the framework of the extended molecular exciton Davydov approach. Model calculations show that the strong couplings between the high frequency ν(XH) and low-lattice vibration frequencies, Ω_i, generate the broadness of the ν(XH) band but the multi-Fermi resonances between the ν(XH) state and overtones or combinations of internal modes generate the complicated substructure band which is observed experimentally.     

Application of the ISM EoS for polymer solutions and blends

A method for predicting an analytical equation of state for polymer mixtures and blends from surface tension and liquid state density at normal (ordinary) temperature (γ_n, ρ_n), as scaling constants, is presented. B₂(T) follows a promising corresponding-states principle. Calculation of (T) and b(T), the two other temperature-dependent constants of the equation of state, are made possible by scaling. As a result, γ_n and ρ_n are sufficient for determination of thermophysical properties of polymer mixtures and blends.

We applied the procedure to predict liquid density of poly(ethylene glycol) (PEG-200) + 1-octanol solutions and poly(propylene glycol) (PPG) + poly(ethylene glycol) (PEG-200) blends at compressed state with temperature range from 298.15 to 338.15 K and pressures up to 40 MPa. In this work, the ISM EoS is extended to polymer mixtures and blends as well as pure case without proposing any mixing rule.     

Morphology and tensile properties of glass bead filled low density polyethylene composites: MATERIAL PROPERTIES

The mechanical properties of glass bead filled low density polyethylene (LDPE) composites in tension have been investigated by using an Instron material testing machine. It is found that with increase of the glass bead weight fraction (φ) the tensile modulus (E_c) and the tensile yield stress (σ_yc) increase as a form of nonlinear function but contrary to the elongation strain at break; the correlation between E_c and φ accords with the logarithmic mixing rule and the relationship between σ_y and the volume fraction (φ_f) can be described by means of a second order equation; the effects of the glass bead diameter on the mechanical properties are not large; when φ and the bead size are suitable, the enhanced toughness effect of the filled-systems is more significant; the tensile strength of the glass bead filled system pretreated with a coupling agent are somewhat greater than those of the untreated system. In addition, the morphology of the samples is studied to explain the relationship between the micro-structure and the mechanical properties of the composites.     

The optical properties of polymethylmethacrylate polymer dispersed liquid crystals

The effect of the addition of polymer liquid crystals as dispersed molecules to polymethylmethacrylate (PMMA) on the optical properties in the UV-visible and near infrared regions is investigated. From transmission, absorption and reflection spectra the absorption coefficient (ω) and refractive index (n) at angular frequency of radiation (ω) have been calculated at room temperature. The values of the optical band gap (E_opt) have been obtained from the direct allowed transitions in k-space. The width of the tails of localized states in the band gap (ΔE) was evaluated from Urbach edges. Both the parameters (E_opt) and (ΔE) vary with the mixing ratio of dispersed liquid crystals.     

Transport phenomenon as a function of counter and co-ions in solution: chronopotentiometric behavior of anion exchange membrane in different aqueous electrolyte solutions

Anion exchange membrane has been investigated in different electrolyte solutions by chronopotentiometry to explore the influence of co-ion and counterion of the exchange group of the membrane, on the transport phenomena. Chloride, nitrate, sulfate and acetate in sodium salts were used as counterions and sodium, potassium, calcium and ammonium in chloride salts were used as co-ions. The membrane showed a potential drop (E₀) in all these electrolytes when a constant current was applied across it, which remained constant for a period less than τ, called the transition time and rose gradually to a maximum (E_max) value. The parameters such as τ, E₀ and E_max and the potential jump (ΔE) and τ and the inflection zone (Δt) along the time axis have been measured and compared at an applied current density (I) of 10 mA cm⁻² in 10 mM solutions. The values of τ^1/2/z_A[A₀] or τ^1/2/z_C[C₀], with or , E₀ and ΔE with or (where r_A and r_C are the ionic radii of counter and co-ions, respectively) have been correlated. Permselectivity (P) and transference number of the membrane with respect to each one of the above electrolytes have been evaluated and discussed.     

Kinetic analysis of thermogravimetric data obtained under linear temperature programming—a method based on calculations of the temperature integral by interpolation

A new technique, called interpolation method, with general application in the kinetic analysis of processes studied by thermogravimetry (TG) under linear temperature programming is developed. It is based on the linear relationship, with slope 1, between log g() and log I(γ, θ) for the appropriate kinetic function, where I(γ, θ) is the normalized temperature integral, θ the normalized temperature (θ=T/T₀) and γ a dimensionless activation energy (γ=E/RT₀). Values of log I(γ, θ) are calculated by linear interpolations in a pre-built table. This method can easily be programmed and implemented in a personal computer, where the results (kinetic parameters and quality of regressions for the kinetic functions considered) are typically obtained in a very short time. The method is validated by analyzing different simulated thermogravimetric curves and comparing the results with those determined with some classic methods taken from the literature. In addition, the results are compared with the values obtained by a similar method, also developed and explained in this paper, which involves the evaluation of all the values of the temperature integral by numerical integration, therefore, demanding a much larger calculation time. The interpolation method is found to be more accurate than other published methods, particularly in the case of thermogravimetric curves corresponding to processes with low activation energies. The results obtained are always similar to those determined by the integration method, which is taken as reference. Application of the technique to experimental data for various types of reactions shows that the results are in agreement with the published parameters and kinetic laws.     

Vibrational spectra and density functional study of propylgermane

Raman and infrared spectra of propylgermane, CH₃CH₂CH₂GeH₃, and its Ge-deuterated analog, CH₃CH₂CH₂GeD₃, were investigated in their gaseous, liquid and solid states. The normal coordinate treatment was carried out by density functional theory (DFT) calculation, using B3LYP/6-31G^* and 6-311++G^** basis sets, and the corresponding fundamental vibrations were assigned. The trans (T) and gauche (G) forms around the central C–C bond coexisted in the gaseous and liquid states and only the T form existed in the solid state. From the temperature dependent measurements of the Raman spectra in the liquid state, the enthalpy difference was found to be ΔH(T−G)=−0.36±0.02 kcalmol⁻¹ with the T form being more stable. The energy differences between the isomers obtained by DFT calculations were ΔE(T−G)=−0.46 kcalmol⁻¹ and ΔE(T−G)=−0.87 kcalmol⁻¹ by the 6-31G^* basis set and 6-311++G^** basis set, respectively.     

The ν(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids. Phenomenology and formation models

The infrared spectra of phosphinic acid R₂POOH dimers (R=CH₃, CH₂Cl, C₆H₅) have been studied in CCl₄ and CH₂Cl₂ solutions (T=300 K). The infrared spectra of deuterated R₂POOD dimers (R=CH₃, CH₂Cl) were also studied in the gas phase (T=400–550 K) and solid state (T=100–300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T=12–30 K) in the 4000–400 cm⁻¹ spectral region. It is found that the strong and broad ν(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12–600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the ν(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O–HOP in a cyclic complex plays virtually no role in the mechanism of the ν(OH/OD) band formation; the shape of ν(OH/OD) band is controlled mainly by the POOH(D)O fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 3500–1500 cm⁻¹.     

Influence of temperature on surface tension of three liquid crystal polymers and polyethylene terephtalate

In this work Pressure Volume Temperature (PVT) data for three different liquid crystal polymers (LCPs), namely Vectra A950^® and two LCPs based on 4,4'-dihydroxybiphenyl (PB-n) (where n is the number of methylene units present in the polymer) and polyethylene terephtalate (PET), were obtained for temperatures ranging from 50 to 300°C and pressures ranging from 0.1 to 200 MPa. The experimental data were fitted to the Flory-Orwoll-Vrij equation of state and used to predict the influence of temperature on the surface tension of the four materials studied.

The surface tension of PET was shown to decrease linearly with increasing temperature. The surface tension of both PB-11 (γ_PB-11) and Vectra A950^® (γ_Vectra) decreased linearly with increasing temperature for temperatures corresponding to the nematic phases of the materials. Abnormal behaviour was observed for the surface tension of PB-8 (γ_PB-8): at temperatures just above T_b (the temperature at which the material became birefringent), γ levelled off and then decreased. A clear discontinuity was observed for both γ_PB-8 and γ_PB-11 near the mesophase to isotropic transition. For both PB-8 and PB-11, γ decreased linearly with increasing temperature for temperatures corresponding to the isotropic phases of the materials.     

Thermoelectric properties of perovskites: Sign change of the Seebeck coefficient and high temperature properties

The possibility to change the Seebeck coefficient sign has been evidenced in the LaCoO₃ perovskites. A small hole doping (Co³⁺/Co⁴⁺) will result in a large positive Seebeck coefficient, while a small electron doping (Co²⁺/Co³⁺) will give a large negative Seebeck coefficient at room temperature. This mechanism is shown to be efficient as well in 1D Ca₃Co₂O₆ deriving from hexagonal perovskites. By doping Ca₃Co₂O₆ with Ti⁴⁺, a mixed valency Co²⁺/Co³⁺ is introduced and the thermopower turns negative.

At high temperature, the Seebeck coefficients of LaCoO₃ and related compounds decrease to small values due to the spin state transition. The values converge towards a positive value, close to +20 μV/K at 800 K. This suggests that at high T, the Seebeck coefficients in the case of localized charges do not depend on the doping, but only on the spin and orbital degeneracies. On the other hand, in the case of metallic-like samples as electron-doped manganites, the properties can be described up to high T in terms of a single-band metal. Due to the linear variation of S as a function of T and the almost constant value of ρ, the ratio S²/ρ which is crucial for high temperature applications increases.     

New regularities and an equation of state for liquids

Three regularities have been introduced for liquids (T < T_C and ρ > ρ_C) based on average potential energy. The experimental data have been used to show the validity of the regularities. First, there exists near-linearity relation between and ρ for all isotherms of a liquid, where P_i and ρ are internal pressure and density, respectively. Second, changes linearly with ρ for each isotherm of any liquid, where Z and V_m are compressibility factor and molar volume, respectively. Third, a new regularity using the definition of bulk modulus and our new equation of state between reduced bulk modulus and density has been introduced, that is versus ρ must be linear for all isotherms of a liquid where B_r is the reduced bulk modulus.

A new equation of state has been also derived. The density of some liquids in the extensive ranges of temperature and pressure has been calculated using the new equation of state. The densities calculated from this equation agree with experiment to better than 0.3%. The new equation of state can predict internal pressure, thermal expansion coefficient, and isothermal compressibility of liquids within experimental error.     

Structural and spectroscopic properties of Hexamethylenetetramine cobalt(II) complex: [Co(NCS)2(hmt)2(H2O)2][Co(NCS)2(H2O)4] (H2O)

Synthesis, structure, spectroscopy and thermal properties of complex [Co(NCS)₂(hmt)₂(H₂O)₂][Co(NCS)₂(H₂O)₄] (H₂O) (I), assembled by hexamethylenetetramine and octahedral Co(II) metal ions, are reported. Crystal data for I: F_w 387.34, a=9.020(8), b=12.887(9), c=7.95(1) Å, =96.73(4), β=115.36(5), γ=94.16(4)°, V=820(1) Å³, Z=2, space group=P−1, T=173 K, λ(Mo-K)=0.71070 Å, ρ_calc=1.718567 g cm⁻³, μ=17.44 cm⁻¹, R=0.088, R_w=0.148. An interesting two-dimensional network is assembled via hydrogen bonds through coordinated and free water molecules. The d–d transition energy levels of Co(II) ion are determined by UV–vis spectroscopy and calculated by ligand field theory. The calculated results agree well with experiment ones.     

Rotational excitation of ions produced by the He(2 S) Penning ionization of CO and N2

Rotational-state distributions of the CO⁺ (A–X, B–X) and N₂⁺(B–X) emissions produced by the collisions of He(2 ³S) with CO and N₂ were studied in the collision energy (E_R range 100–200 meV. The rotational populations of the emitting states can be fitte by single Boltzmann temperatures (T_R. The T_R (320 ± 30 K) for the ν′ = 3 and 4 levels of the CO⁺ (A²Π) state are nearly independent of, or slightly increase with, E_R, while T_R for the CO⁺(B²Σ⁺, ν′ = 0) state increases rapidly with E_R.The T_R (430 ± 20 K) for the N₂⁺(B²Σ⁺, ν′ = 0) state is nearly independent or slightly decreases with increasing E_R. Interactions providing these trends are discussed.     

Density and refractive index measurements in hexaheptyloxytriphenylene, a discotic liquid crystal

Density and refractive index measurements in the discotic liquid crystal hexaheptyloxytriphenylene were performed in the hexagonal columnar Col_ho and isotropic I phases. The temperature dependence of the density ρ(T) for this compound was obtained by combining small angle X-ray data and capillary methods. The ordinary n_o extraordinary n_e and isotropic liquid n_i refractive indices were measured using a modified Abbe refractometer to an accuracy of about 10^-3. To check the consistency of the density and the refractometry experiments we used the Lorentz-Lorenz relation. An anomaly in the empirical relationship at the Col_ho-I phase transition, which holds for many uniaxial liquid crystals, was detected. A discrepancy between low birefringence Δn∼0.109 and a relatively high local electric field anisotropy for hexaheptyloxytriphenylene is discussed.     

Thermodynamic stabilities of NiTeO3 and Ni3TeO6 by solid oxide electrolyte e.m.f. method

The e.m.f. of the galvanic cells Pt,C,Te(l),NiTeO₃,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt and Pt,C,NiTeO₃,Ni₃TeO₆,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt (where 15 YSZ=15 mass% yttria-stabilized zirconia) was measured over the ranges 833–1104 K and 624–964 K respectively, and could be represented by the least-squares expressions E₍₁₎±1.48 (mV) = 888.72 − 0.504277 (K) and E_(II) ±4.21 (mV) = 895.26 − 0.81543T (K).

After correcting for the standard state of oxygen in the air reference electrode, and by combining with the standard Gibbs energies of formation of NiO and TeO₂ from the literature, the following expressions could be derived for the ΔG^°_f of NiTeO₃ and Ni₃TeO₆: ΔG_f^°(NiTeO₃) ± 2.03 (kJ mol⁻¹) = −577.30 + 0.26692T (K) and ΔG^°_f(Ni₃TeO₆)±2.54 (kJ mol⁻¹) = −1218.66 + 0.58837T (K).     

Organometallic complexes for nonlinear optics: Part 31. Cubic hyperpolarizabilities of ferrocenyl-linked gold and ruthenium complexes

The complexes [Fe{η-C₅H₄---(E)---CH=CH---4-C₆H₄CCX}₂] [X=SiMe₃ (1), H (2), Au(PCy₃) (3), Au(PPh₃) (4), Au(PMe₃) (5), RuCl(dppm)₂ (7), RuCl(dppe)₂ (8)] and [Fe{η-C₅H₄---(E)---CH=CH---4-C₆H₄CH=CRuCl(dppm)₂}₂](PF₆)₂ (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1–8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the Fe^II/III couple of the ferrocenyl groups, 6–8 also showing reversible (7, 8) or non-reversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1–5; in contrast, complexes 6 and 7 exhibit large negative γ_real and large γ_imag values. A factor of 4 difference in γ and two-photon absorption cross-section σ₂ values for 6 and 7 suggest that they have potential as protically switchable NLO materials.     

Molecular weights of polystyrenes in toluene solutions by light scattering. Comparison between classical values and values deduced from a new method

Light scattering measurements in toluene solutions are performed for a series of monodisperse polystyrenes with a molecular weight M_w range from 4×10³ to 8×10⁶. The scattered polarized intensities I_v and the natural depolarization ratios ρ_n are registered with different apparatus at λ=633 or 488 nm and the M_w values are deduced through different formulae. The complete Carr and Zimm formula (CL_a), from I_v and ρ_n, and the usual simplified formula (CL_b), from I_v, are considered for the classical method. An already demonstrated formula is considered for the new method (New). Values of M_w and related parameters do not depend on the experimental systems used but deviations appear when using different formulae. The deviations are generally low (about 10%) but often systematic: M_w(CL_a)<M_w(CL_b)<M_w(New). The most important difference concerns the effect of destructive interferences for M_w>5×10⁵: the new formula leads to a lower increase from θ=90° to θ→0 for M_w values (θ is the observation angle). For instance, in the 8×10⁶ sample, M_w(θ→0)/M_w(θ=90°)=3.6 instead of 6.1, which implies a revision of the usual determination of the radius of gyration, R_g.     

Analysis to obtain precise density fluctuation of supercritical fluids by small-angle X-ray scattering

A procedure of analysis for small-angle X-ray scattering (SAXS) data has been established to obtain density fluctuation of supercritical fluids near the critical point. It is indispensable for the certain analysis to utilize both of high-quality SAXS data measured under stable thermodynamic condition and accurate P–ρ–T data in supercritical region. As a standard example, SAXS measurements have been performed for supercritical CO₂, which is a suitable sample satisfying the condition for both experiment and analysis. The measurements were carried out along four isothermal conditions at reduced temperature of T_r = T/T_c = 1.020, 1.022, 1.043 and 1.064. Comparing the experimental density fluctuation with calculated one from the most reliable equation of state, the differences are within 8% at most.     

宏观均相多孔电极电化学阻抗谱基础

电化学阻抗谱可用于诊断多孔电极内电荷转移反应,即界面电荷集聚和电荷传导,以及反应物质输运。本文采用复相量方法,在同态假设条件下,重新推演多孔电极阻抗谱模型,厘清传统多孔电极阻抗谱模型中的模糊性表述。(1) 定义多孔电极表征输入参数,包括电极基体电子电导率σ₁ 、电解质离子电导率σ₂、界面电荷传递电导率g_ct、单位面积界面电容C、固相扩散系数D、速度常数k、电极厚度d、特征孔深L_p 和单位体积表面积S_c;(2) 解析阻抗谱特征输出参数,包括场扩散常数K,特征频率ω₀、ω₁、ω₂、ω₃和 ω_max,它们分别相关于界面传导反应、有限场扩散、氧化还原反应、孔内扩散和最小特征孔尺寸,以及分别对应于从传导到扩散和从扩散到饱和的转折频率f_k1 和f_k2;(3) 当参数X和Z同时变化时(X = σ₁和Z = d,S_c,L_p,C,g_ct,D,k),通过阻抗谱特征参数的演变规律,分析了电荷转移反应中X和Ζ参数耦合竞争;(4)为深入分析电荷转移反应中参数X和Z的耦合竞争,引入了分叉频率f_XZ和f_ZX 。f_XZ和f_ZX所处位置可以用于表征参数X和Z影响电荷转移反应的深度和广度。当分叉频率f_XZ和f_ZX不存在时,表明电荷转移反应中参数X和Z在全频率范围内存在耦合竞争。总之,借助于特征频率和分叉频率,本文一方面研究了动力学参数和微观结构参数对多孔电极中电荷转移反应的影响,另一方面分析谱图的变化及其背后的阻抗谱特征演化规律。本文研究结果可为阻抗谱的系统仿真和辨识提供理论基础,可为多孔电极内电荷转移反应的竞争分析提供技术支撑,还可为电化学储能系统的优化设计提供诊断工具。