The frequency dispersion of dynamic transfer coefficients and elastic moduli of magnetic liquids

The analytic equations for viscosity coefficients and the corresponding elastic moduli obtained in [3] were used to calculate these values over a wide range of reduced frequency values (ω* ≈ 10^?7?10). The volume η _v (ω) and shear η _s (ω) viscosity coefficients decreased as the frequency increased. The dispersions η _v (ω) and K _r (ω) were only caused by the contribution of structural relaxation, and the dispersions η _s (ω) and μ(ω), by translational and structural relaxation. The shear elastic modulus μ(ω) and relaxation volume elastic modulus K _r (ω) increased as the frequency grew. The results obtained were in satisfactory agreement with the conclusions from general relaxation theory.     

The synthesis and thermodynamic properties of strontium fluoromanganite Sr<Subscript>2.5</Subscript>Mn<Subscript>6</Subscript>O<Subscript>12.5 − δ</Subscript>F<Subscript>2</Subscript>

The existence of the [SrF_0.8O_0.1]_2.5[Mn₆O₁₂] = Sr_2.5Mn₆O_{12.5 ? δ}F₂ compound was established in the SrO-Mn₂O₃-SrF₂ system at 900°C and p(O₂) = 1 atm. The crystal structure of strontium fluoromanganite was determined from the X-ray powder diffraction data, electron diffraction, and high-resolution electron microscopy. It can be described in the monoclynic system with four Miller hklm indices: hklm: H = h a* + k b* + l c ₁ ^* + m q ₁, q ₁, q ₁ = c ₂ ^* = γc ₁ ^* , γ ≈ 0.632, a ≈ a ≈ 9.72 Å, b ≈ 9.55 Å, c ₁ ≈ 2.84 Å, c ₂ ≈ 4.49 Å, monoclinic angle γ ≈ 95.6°. The electromotive force method with a solid fluorine ion electrolyte was used to refine the composition of fluoromanganite and determine the thermodynamic functions of its formation from phases neighboring in the phase diagram (SrMn₃O₆, Mn₂O₃, SrF₂, and oxygen), ΔG°, kJ/mol = ?(111.7 ± 1.9) + (89.5 ± 1.5) × 10^?3 T.     

Formation of mononuclear rhodium(III) sulfates: <Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study

It was shown that the monomeric rhodium sulfate complexes [Rh(H₂O)₄(SO₄)]⁺, trans-[Rh(H₂O)₂(SO₄)₂]^?, cis-[Rh(H₂O)₂(SO₄)₂]^?, and [Rh(SO₄)₃]^3? were not predominant forms in aqueous solutions. The ¹⁰³Rh NMR chemical shifts of the complexes were assigned, and the conditions for their formation in solutions, concentration parameters, and acidity at which the fraction of the monomers was maximal were determined. The constants of formation of the complexes and ion pair (IP) were estimated: K _IP = 8 ± 3.5, K ₁ ≈ 8, K _2trans ≈ 1, K _2cis ≈ 1, and K ₃ ≈ 2.     

Structure of the hexanuclear Cu(II) β-diketonate complex

The structure of the hexanuclear copper(II) β-diketonate complex with gfa (hexafluoroacetylacetone) and dpm (dipivalylmethanate) ligands was studied by low-temperature (T = 100 K) X-ray diffraction. Crystal data for Cu₆(gfa)₄(dpm)₄(OH)₄ [C₆₄H₈₄Cu₆F₂₄O₂₀]: a = 28.2364(7) Å, b = 12.8072(3) Å, c = 24.7199(7) Å, β= 115.900(1)°, V = 8041.5(4) ų, space group C2/m, Z = 4, d _calc 1.661 g/cm³. The coordination polyhedra of the copper atoms — squares and octahedra — are formed by the oxygen atoms of the gfa and dpm ligands and groups. In all cases, the Cu-O distances vary from 1.89 Å to 2.13 Å. The complexes follow the sites of the rhombohedral sublattice with the parameters a _c ≈ 14.4 Å and a _c ≈ 61.5°.     

Molecular dynamics simulation of the structure and thermodynamic properties of liquid rubidium at pressures of up to 10 GPa and temperatures of up to 3500 K

The models of rubidium at temperatures of up to 3500 K, degrees of compression of up to Y = V/V₀ = 0.3, and pressures of up to 32 GPa were constructed by molecular dynamics (MD) using the interparticle potential ЕАМ. The thermodynamic properties of the MD models agree satisfactorily with experiment in the range of parameters under study at rubidium densities higher than 0.86 g/cm³. The behavior of the models in the range of the van der Waals loop was analyzed; the calculated critical temperature of rubidium T_c is ～2250 ± 25 K, density ～0.41 g/cm³, pressure ～0.019 GPa, and compressibility factor Z = pV/RT ≈ 0.137. The states with the unity factor Z = 1 were observed at pressures of up to 0.30 GPa (at ～3000 K); the temperature dependence of the density of the models with Z = 1 is nearly linear, and the Boyle temperature is T_B ≈ 10160 K. The ratio T_c/T_B = 0.221 is close to this value for cesium (0.23) and mercury (0.276). In the temperature and pressure ranges under study, the inversion of the Joule–Thomson coefficient did not take place, but should be observed at pressures of ?0.3 GPa and elevated temperatures. It was found that the diffusion coefficient D(T) dependences do not straighten in the usually used coordinates within wide temperature ranges. It was concluded that the structure of the liquid smoothly changes when the rubidium models are compressed and this reveals in the change of the degree of asymmetry of the first peak of the radial distribution function.     

Coprecipitation of calcium hydroxyapatite,graphene oxide,and chitosan from aqueous solutions

We determined the character of interactions between calcium hydroxyapatite Са₁₀(РO₄)₆(ОН)₂ (HA), graphene oxide (GO), and chitosan (С₆Н₁₁NO₄) _n (CHT) to yield HA/CHT/GO nanocomposites (NCs) in the СаС1₂–(NH₄)₂НРО₄–NH₃–Н₂О–(С₆Н₁₁NO₄) _n –GO system (25°С). A set of physicochemical methods helped us to elucidate composition–synthesis parameters–structure–particle size–properties correlations for the prepared NCs and to prove the feasibility to manufacture NCs with tailored HA, CHT, and GO contents, described by the bulk formula Са₁₀(РО₄)₆(ОН)₂ · х(С₆Н₁₁NO₄) _n · yGO · zН₂О, where х = 0.1, 0.2, 0.3; y = 0.6, 1.2, 2.4; and z = 6.0–7.4.     

An analysis of the vibrational structure of the UV absorption spectrum of methacryloyl chloride vapor

An analysis of the vibrational structure of the UV spectrum of methacryloyl chloride vapor was performed. The spectrum contained unique information about the torsional vibration levels of the trans and cis isomers in the ground (S ₀) and excited (S ₁) electronic states. 136 absorption bands were revealed, and ～85% of them were assigned. The 0-0 transition frequencies of the trans and cis isomers were found. Several Deslandres tables were constructed for torsional vibrations from 0-0 transition frequencies and “local origins” corresponding to fundamental and combined frequencies of both isomers. Systems of torsional levels up to high quantum number values (v ≈ 6–8) were determined, and the ω_e harmonic frequencies and χ ₁₁ anharmonicity coefficients were calculated for both isometric forms in the ground (S ₀) and excited (S ₁) states. The results were substantially different from those obtained in an analysis of Fourier-transform IR spectra.     

Percolation in the model of random successive adhesion of anisotropic particles

Numerical studies of random successive adsorption (the RSA model) of rectangular particles on a flat substrate are performed and the dependences of saturation concentration and the percolation threshold on the parameters of a model are determined. The dependences of saturation concentration φ _j∞ on the particle diameter-to-length ratio r and the parameter of orientational order S are found. Correlations between the ? _j∞(r) function and excluded surface area are discussed. It is revealed that for highly ordered systems (S ≈ 1), the saturation concentration φ _j∞ is equal to 0.557 ± 0.005 and is virtually independent of r. For partially ordered systems, the ? _j∞ value decreases with an increase in r and in the r → ∞, ? _j∞ → 0. Percolation transition and electrical connectivity for the systems studied can take place only under the assumption of the tunnel mechanism of conductivity through gaps with finite thicknesses. The minimum thickness of tunnel gaps, at which percolation can occur, rises with increasing r and decreasing S.     

Matrix Assisted and/or Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of WO<Subscript>3</Subscript> Clusters Formation in Gas Phase. Nanodiamonds,Fullerene, and Graphene Oxide Matrices

The formation of W _x O _y ^+●/-● clusters in the gas phase was studied by laser desorption ionization (LDI) and matrix assisted laser desorption ionization (MALDI) of solid WO₃. LDI produced (WO₃) _n ^{+ ●/- ●} (n = 1-7) clusters. In MALDI, when using nano-diamonds (NDs), graphene oxide (GO), or fullerene (C₆₀) matrices, higher mass clusters were generated. In addition to (WO₃) _n ^-● clusters, oxygen-rich or -deficient species were found in both LDI and MALDI (with the total number of clusters exceeding one hundred ≈ 137). This is the first time that such matrices have been used for the generation of(WO₃) _n ^+●/-● clusters in the gas phase, while new high mass clusters (WO₃) _n ^-● (n = 12-19) were also detected.

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Graphical Abstract

     

Dissolution kinetics of silver metal nanoparticles in their reaction with nitric acid in an reverse micelle solution of AOT

The dissolution of silver nanoparticles in their reaction with aqueous HNO₃ solubilized to an reverse micelle solution of sodium bis(2-ethylhexyl)sulfosuccinate in decane is studied spectrophotometrically. A physicochemical model is advanced for quantifying the process kinetics on th basis of the following autocatalytic scheme: Ag⁰ + H⁺ + NO ₃ ^? → Ag⁺ + products (k ₁), and Ag⁰ + Ag⁺ + NO ₃ ^? → 2Ag⁺ + products (k ₂). The effective rate constant k ₂ decreases with decreasing solubilization capacity V _S/V _O (where V _S is the volume of the solubilized dispersed aqueous phase and V _O is the volume of the micelle solution); the solubilization capacity determines the size of the micelle cavities in which the reaction between Ag⁰ and HNO₃ occurs: k ₂ = 74 (V _S/V _O) · 100% ≈ 3.8%), 41 (2.9), and 35 (2.0) L/(mol s). The effective constant k ₁ is determined with a high uncertainty; the effect of V _S/V _O on k ₁ has the opposite tendency.     

Differential thermogravimetric curves for a mixture of evaporable and degradable chain oligomers

Since the boiling point of oligomers increases with increasing chain length, differential thermogravimetric (DTG) curves of polymerization products are uniquely related to the molecular mass distribution of the oligomers in the chain length region in which the degradation rate is less than the rate of evaporation. Degradation is manifested by narrow, chain length-invariant peaks of the DTG curves so that they are distinguishable from broad DTG bands due to the evaporation of the mixture of oligomers. The detachment of the terminal groups at a temperature T₁ and main chain scission at T_d > T₁ are accompanied by dimerization of macroradicals, evaporation of the dimers in the T₁ < T < T_d interval, and appearance of the full degradation peak at T ≈ T_d. The pattern of DTG curves based on these concepts has been calculated on the assumption of free convection in the boundary layer and a spatially uniform degradation in the melt. As an example, DTG curves for the products of tetrafluoroethylene polymerization in liquid solutions have been considered.     

Extensional rheology of cellulose/NaOH/urea/H<Subscript>2</Subscript>O solutions

The extensional flow behaviors of cellulose/NaOH/urea/H₂O solution were investigated by using capillary breakup extensional rheometry (CaBER). The effects of temperature, storage time and cellulose concentrations on both the storage modulus G′ and the loss modulus G″ were also analyzed. For 2 wt% cellulose solution, the G′, G″ and filament lifetime remained unchanged after long storage time. While, for 4 wt% cellulose solution, physical gels could form at either higher temperature or for longer storage time, and the filament lifetime, the relaxation time (λ _e ) and the initial extensional viscosity (η _e0) first increased and then decreased with increase of the storage time. The transition points of the filament lifetime shifted to lower storage time with the increase of the temperature. The η _e0 is proportional to λ _e . The results presented suggest that the extensional properties of the cellulose/NaOH/urea/H₂O solution first increase and then decrease during the gelation process, and the spinning time, which decreases linearly with the increase in the storage temperature, must be controlled below the time that η _e0 starts to decrease.     

The internal rotation potential functions of the methacryloyl chloride molecule in the ground and excited electronic states

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S ₀) and excited (S ₁) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S ₀ and S ₁ electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S ₀ state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.     

Solubility of B-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> and the Hydrolysis of Niobium(V) in Aqueous Solution as a Function of Temperature and Ionic Strength

B-Nb₂O₅ was recrystallized from commercially available oxide, and XRD analyses indicated that it is stable in contact with solutions over the pH range 0 to 9, whereas solid polyniobates such as Na₈Nb₆O₁₉?13H₂O(s) appear to predominate at pH>9. Solubilities of the crystalline B-Nb₂O₅ were determined in five NaClO₄ solutions (0.1≤I _m /mol?kg^?1≤1.0) over a wide pH range at (25.0±0.1)?°C and at 0.1 MPa. A limited number of measurements were also made at I _m =6.0 mol?kg^?1, whereas at I _m =1.0 mol?kg^?1 the full range of pH was also covered at (10, 50 and 70)?°C. The pH of these solutions was fixed using either HClO₄ (pH≤4) or NaOH (pH≥10) and determined by mass balance, whereas the pH on the molality scale was measured in buffer mixtures of acetic acid?+?acetate (4≤pH≤6), Bis-Tris (pH≈7), Tris (pH≈8) and boric acid?+?borate (pH≈9). Treatment of the solubility results indicated the presence of four species, \(\mathrm{Nb(OH)}_{n}^{5-n}\) (where n=4–7), so that the molal solubility quotients were determined according to:

$0\mathrm{.5Nb}_{2}\mathrm{O}_{5}\mathrm{(cr)+0}\mathrm{.5(2}n-5\mathrm{)H}_{2}\mathrm{O(l)}_{\leftarrow}^{\to}\mathrm{Nb(OH)}_{n}^{5-n}+(n-5)\mathrm{H}^{+}\quad (n=4\mbox{--}7)$

and were fitted empirically as a function of ionic strength and temperature, including the appropriate Debye-Hückel term. A Specific Interaction Theory (SIT) approach was also attempted. The former approach yielded the following values of log?₁₀ K _sn (infinite dilution) at 25?°C: ?(7.4±0.2) for n=4; ?(9.1±0.1) for n=5; ?(14.1±0.3) for n=6; and ?(23.9±0.6) for n=7. Given the experimental uncertainties (2σ), it is interesting to note that the effect of ionic strength only exceeded the combined uncertainties significantly in the case of log?₁₀ K _s6 to I _m =1.0 mol?kg^?1, such that these values may be of use by defining their magnitudes in other media. Values of Δ _f G ^o, Δ _f H ^o, S ^o and \(C_{p}^{\mathrm{o}}\) (298.15 K, 0.1 MPa) for each hydrolysis product were calculated and tabulated.

     

Analysis and characterization of the transition from the Arrhenius to non-Arrhenius structural relaxation in fragile glass-forming liquids

We have studied the transition from an Arrhenius-like to a non-Arrhenius-like structural relaxation behavior in fragile glass-forming liquids. This transition is denoted by the temperature T_A that usually occurs above the melting point T_m and the dynamic crossover temperature T_B. Recent studies reveal that T_A is a characteristic temperature related with the dynamical properties of the system. However, its unambiguous determination is not easy. In this work, a method to obtain the temperature T_A from the experimental data of α-relaxation time is presented. The obtained T_A is compared with the cooperativity onset temperature T_x extracted from the bond strength–coordination number fluctuation model. The result reveals that T_A is close to T_x for fragile liquids. From the result of the present analyses combined with the linear relation T_x \(\propto\) T₀, where T₀ is the Vogel temperature, the Arrhenius crossover phenomenon in fragile liquids is linked to the low-temperature structural relaxation dynamics.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Binuclear copper(II) complexes with acyldihydrazones of 1,4-cyclohexanedicarboxylic acid

The binuclear copper(II) complexes with acyldihydrazones formed by 1,4-cyclohexanedicarboxylic acid and salicylaldehyde or 2-hydroxyacetophenone were synthesized and studied. The structure of the complex with 1,4-cyclohexanedicarboxylic acid bis(salicylidene)hydrazone (H₄L¹) [Cu₂L¹(Py)₂] was studied by X-ray diffraction. The crystals are triclinic: a = 8.1852(4) Å, b = 8.5157(5) Å, c = 11.6553(7) Å, α = 80.678(3)°, β = 70.041(4)°, γ = 74.803(3)°. Space group \(P\bar 1\), Z = 1. The number of symmetrically independent reflections with I > 2(σ(I)) is 2245, R = 0.0395; R _w = 0.0917. The complex contains two equivalent copper atoms located at a 10.772 Å distance from each other. The coordination polyhedra have a square geometry and are involved in the intermolecular π/π-stacking. The EPR spectra of solutions of the binuclear complexes show an isotropic signal of seven HFS lines (g = 2.113–2.118, A _Cu ≈ 38 G), indicating interaction between the unpaired electrons and the two equivalent copper nuclei. The possible exchange interaction channels were analyzed.     

Determination of the molecular masses of tetrafluoroethylene telomers by gel-permeation chromatography

Gel-permeation chromatography has been employed to study the molecular-mass distribution of tetrafluoroethylene telomers prepared through γ irradiation of 0.05–0.56 mol/l monomer solutions in acetone. The molecular-mass-retention-volume V _R calibration dependence has been plotted from chromatograms of perfluoroenanthic and perfluoropelargonic acids (F(CF₂-CF₂) _n COOH; n = 3 or 4, respectively). The measured V _R-log n curve is located parallel to that plotted earlier for oligo(oxyethylene glycol)s (OH-(CH₂-CH₂O) _n -OH) and is shifted along the volume axis. The shift value is determined by the ratio between logarithmic volumes of chain units of these oligomers. The shift agrees with the assumption that the retention volumes of oligomers with the same spatial chain structure are proportional to the logarithm of the ratio between their van der Waals volumes. This assumption is supported by the quantum-chemical calculation of the molecular volumes of oligomers composed of (CH₂-CH₂) _n , (CH₂-CH₂O) _n , and (CF₂-CF₂) _n fragments. As the concentration of tetrafluoroethylene in the initial solution is increased, the average length of (CF₂-CF₂) _n chains increases from \(\bar n\) ≈ 3 to \(\bar n\) ≥ 8. The maximum values of n = 12–15 are determined by the solubility limit of telomers in THF.     

RAFT polymerization of linear ABC triblock copolymer P<Emphasis Type="Italic">t</Emphasis>BA-<Emphasis Type="Italic">b</Emphasis>-PS-<Emphasis Type="Italic">b</Emphasis>-P2VP and regulation of its hierarchical self-assembly structure in solution

Linear ABC triblock copolymer PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ was successfully synthesized by RAFT polymerization. Block copolymer micelles were prepared by the two-step hierarchical self-assembly process. Size exclusion chromatography and ¹H NMR were used to characterize the structure of samples. Morphologies and size of micelles were determined by transmission electron microscope. The results showed that the densely dispersed spherical micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were obtained in the first step of the hierarchical self-assembly process. In the second step, core-compartmentalized micelle strings with different lengths and distribution densities were obtained when the primary self-assembled solution was dialyzed in distilled water with pH ≈ 3. When distilled water with pH ≈ 3 was added drop-wise to this solution, uniformly dispersed spherical core-compartmentalized micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were prepared. Thus, hierarchical self-assembly structure of linear ABC triblock copolymer was obtained successfully and the preparation of uniformly dispersed spherical micelles of triblock copolymers was realized simply by changing the secondary self-assembly methods.     

Temperature-dependent AC electrical conductivity,thermal stability and different DC conductivity modelling of novel poly(vinyl cinnamate)/zinc oxide nanocomposites

Thermal analysis on organically modified Ca²⁺-montmorillonite (OMON) and its source materials—octadecylamine (ODA) and Ca²⁺-montmorillonite (Ca²⁺-Mon)—was studied using thermally stimulated current (TSC) technique. The appearance of ρ _MON peak with the T _max = 75 °C shows the ability of the developed TSC system to demonstrate the relaxation effects of dehydration in Ca²⁺-Mon. It appeared within the temperature range of DSC endothermic peak (30–100 °C) where the T _mMON = 58 °C. Segmental motions of ODA chains and structural disruptions in the modifier agent compound produced TSC α _ODA, ρ _ODA and ρ _1ODA peaks that are comparable to thermal transition and endothermic peaks in DSC profile (T _gODA, T _m1ODA and T _m2ODA). The effect of localized motion in ODA chains as revealed by the TSC β_OMON peak (T _max = ?23 °C), however, is absent in the DSC profile of OMON. It shows TSC technique has high sensitivity in detecting various relaxation behaviors at molecular level. More evidences are demonstrated by the ρ _OMON (T _max = 86 °C) and ρ _1OMON (T _max = 105 °C) peak originated from the ODA chains structures. These peaks also confirm the intercalation of the modifier cations inside the Ca²⁺-Mon gallery.