The origin of the Poisson ratio of amorphous organic polymers and inorganic glasses

Studies concerning the relationship between the value of μ and a number of mechanical and thermal properties of amorphous polymers and glasses are analyzed with the aim to gain information about the origin of Poisson ratio μ in these systems. It is shown that the Poisson ratio features a more pronounced structure-sensitive behavior than the elastic modulus, although the Poisson ratio varies in a narrow range. The relationship between the Poisson ratio and the Grüneisen parameter is substantiated. In this context, the issue of the correlation between harmonic and anharmonic quantities is highlighted. The Poisson ratio is sensitive to lattice dynamics and atomic–molecular structures of polymers and glasses. When light atoms, for example, hydrogen atoms in polyethylene, are replaced with larger and heavier atoms on pendant chains of the macromolecular backbone, anharmonicity increases; that is, lattice Grüneisen parameter γ_D increases. As a result, the Poisson ratio increases because these quantities are related unambiguously. Conditions of preparing an isotropic material with a negative Poisson ratio (μ < 0) are discussed. The relative ultimate strain of the interatomic bond in glassy systems is a function of the Poisson ratio solely. The frozen elastic strain of amorphous polymers and glasses is likewise a single-valued function of the Poisson ratio. The discussed phenomena are interpreted in terms of the Kuz’menko and Pineda theories and the Berlin–Rothenburg–Bathurst model.     

Inclusion of the concentration dependence of the diffusion coefficient in the sand equation

The applications of the Sand equation in potentiometry of electrode and membrane systems for precise measurements of the transition time (τ) have been determined. An approach was suggested for choosing the diffusion coefficient of electrolyte (D) in the case when the concentration changes from its value in the agitated solution (where D = D_b) to the nearly zero value at the surface (D = D₀ corresponds to an infinitely dilute solution), D_b and D₀ being substantially different. The Nernst–Planck–Poisson nonstationary equations were numerically solved in a one-dimensional system including an ion-exchange membrane and two adjacent diffusion layers (for the electrode–solution system, the result is a particular case). An effective value D_ef was found, whose substitution in the Sand equation gave τ identical to that obtained by numerical solution. The neglect of the concentration dependence D(с) can lead to a nonadequate determination of the ion transport numbers in the membrane.     

Atomic interaction parameters for lanthanides and actinides

A correlation between the Mie-Lennard-Jones interatomic potential and the position of the element in the Periodic Table is used to correct the parameters for lanthanides and to estimate the parameters of the interatomic potential of promethium (Pm-61) for two structures. From the similarity in the double periodicity for the lanthanides and actinides, the minimum coordinates of the interatomic potential r _o are estimated for the elements from curium (Cm-96) through dubnium (Db-105). From the fact that, for Z _a > 60, r _o decreases with increasing atomic number Z _a for the elements of one column, r _o for roentgenium (Rg-111) is estimated. The corrected parameters of the potential are predicted for the elements from francium (Fr-87) through dubnium (Db-105). From the derived parameters of the interatomic potential, the Debye temperatures and the Grüneisen parameters are calculated for neptunium (Np-93) and americium (Am-95).     

First-principles study of the crystal structure and equation of state of naphthaline and anthracene

A first — principles method of density functional theory with a gradient approximation of the exchange-correlation potential in the form of PBE implemented in the PWscf program of the Quantum ESPRESSO software using the Grimme’06 scheme is used to calculate the crystal structure of naphthaline and anthracene at a hydrostatic pressure ranging from 0 GPa to 2 GPa and from 0 GPa to 20 GPa respectively; their equations of states are analyzed. It is shown that under pressure the volume decreases due to voids, and the molecules themselves are practically not deformed. The Grüneisen parameter is calculated in the Slater-Dugdale-MacDonald-Zubarev-Vashchenko model. This parameter decreases from the equilibrium values of 2.356 (anthracene) and 3.226 (naphthaline) with an increase in the pressure. With the use of the Mie-Grüneisen equation under the additional Hugoniot-Renkin condition the impact pressure is calculated, which increases compared to the cold one at a relative compression V/V ₀, below 0.7.     

Intramolecular rearrangements of β-diketonates of metals. A non-emprical study of the structure of Y(MDA)<Subscript>3</Subscript> and La(MDA)<Subscript>3</Subscript> complexes

The structure of tris-complexes of yttrium and lanthanum with malonic dialdehyde (MDA = C₃O₂H₃) is studied by a non-empirical Hartree-Fock method and also with taking into account the electron correlation by the second order Möller-Plesset perturbation theory using the effective pseudo-potentials to describe the atomic cores and two-exponent valence basis sets supplemented with polarization functions. Three most probable geometrical configurations of the D ₃, D _3h , and C ₂ nuclei symmetry are considered for each molecule. The D ₃ structure corresponds to the minimum on the potential energy surface. The D _3h and C _2v configurations correspond to the transition states on the path of two most energetically favorable intramolecular rearrangements. Using the results of our previous calculations for the Sc(MDA)₃ molecule, regularities in the change in molecular parameter values of the series Sc(MDA)₃→Y(MDA)₃→La(MDA)₃ are analyzed. The theoretical and experimental structural and spectral data available in the literature are compared.     

Molecular Dynamics Study on Carbon Dioxide Absorbed Potassium Glycinate Aqueous Solution

Molecular dynamics (MD) simulations have been performed to investigate the effects on structure, transport properties, and dynamical properties in the potassium glycinate aqueous solution caused by carbon dioxide (CO₂) absorption. The optimized structure and charges of constituents of the solution, such as the glycine zwitterion, have been determined by Gaussian09 using the density functional theory. The obtained pair distribution functions, g _ij (r)’s, show the significant distribution difference of bicarbonate ion, \({\text{HCO}}_{3}^{ - }\), around the glycine anion and glycine zwitterion. The shear viscosity and diffusion coefficient obtained by MD show different CO₂ concentration dependences. The frequency dependent diffusion coefficient D _i (ν) for N and C in glycine ions are mainly influenced by the cage effect of surrounding water molecules, whereas D _i (ν) for H show the characteristic vibration due to the structure difference of the glycine ions.     

Properties of solvate shells and the mobility of ions,according to molecular dynamics data

The solvate shells of an ion, its velocity autocorrelation function, and diffusion coefficient D are found, and the interrelations between them are analyzed. A single ion in the system of atoms of a liquid is considered a model system. The interaction between the ion and atoms of the liquid is described by polarization potential U(r); the interaction between atoms of the liquid alone is described by the Lennard–Jones potential. A classical molecular dynamics method is used. Five solvate shells around the ion are found, and the lifetimes of atoms on each shell are calculated. It is found that the velocity autocorrelation function is of a vibrating nature. The spectrum of the autocorrelator and the frequency of cluster vibrations in a linear approximation are compared. Dependences D on parameters of potential U(r) are found. No dependence D on the ion mass is found; this is explained by solvation. The Einstein–Stokes formula and the HSK approximation are used in discussing the results. It is shown that at small radii of the ion, dependence D on parameters U(r) is described by such a model. When the ion radius is increased, the deviation from this dependence and an increase in D are observed. The results are compared to experimental mobilities of O₂^- and Ar₂⁺ ions in liquid argon.     

Dissociation energies of O–H bonds in alkylseleno- and alkyltelluro-substituted phenols

The O?H bond dissociation energy (D _O?H) has been determined for eight alkylseleno-substituted phenols, one alkyltelluro-substituted phenol, and one alkyltelluro-substituted pyridinol. D _O?H has been estimated by the intersecting-parabolas method from kinetic data using five reference compounds: α-tocopherol (D _O?H = 330.0 kJ/mol), 3,5-di-tert-butyl-4-methoxyphenol (D _O?H = 347.6 kJ/mol), 4-methylphenol (D _O?H = 361.6 kJ/mol), 2,6-di-tert-butyl-4-methylthiophenol (D _O?H = 336.3 kJ/mol), and 2,6-di-ter-tbutyl-4-methylphenol (D _O?H = 338.0 kJ/mol). The following D _O?H values (kJ/mol) have been obtained: 335.9 for 2,5,7,8-tetramethyl-2-phytyl-6-hydroxy-3,4-dihydro-2H-1-benzoselenopyran, 342.6 for 2-methyl-5-hydroxy-2,3-dihydrobenzoselenophene, 333.5 for 2,4,6,7-tetramethyl-5-hydroxy-2,3-dihydrobenzoselenophene, 339.4 for 2-tert-butyl-4-methoxy-6-octylselenophenol, 357.9 for dodecyl 3-(4-hydroxyphenyl) propyl selenide, 348.5 for dodecyl 3-(3,5-dimethyl-4-hydroxyphenyl)propyl selenide, 350.9 for dodecyl 3-(3-tert-butyl-4-hydroxyphenyl)propyl selenide, 338.0 for dodecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propyl selenide, 343.0 for 2,6-di-tert-butyl-4-(tellurobutyl-4′-phenoxy)phenol, and 338.8 for 6-octyltelluro-3-pyridinol. The stabilization energies of phenoxyl radicals containing R substituents (X = O, S, Se, Te) have been compared.     

Diffusion and Relaxation Dynamics of Supercooled Polymer Melts

The dynamic properties of polymer melts are investigated in the range of normal liquid regime to the supercooled liquid regime. The polymer is modeled as a coarse-grained bead-spring model with chain length ranging from 5 to 160. The mean squared displacement and non-Gaussian parameter are used to describe the self diffusion of polymer beads. We find slow dynamics with decreasing temperature and increasing chain length. The time evolution of non-Gaussian parameters shows two peaks(or one peak one shoulder) in the α-relaxation time, τα, regime and sub-diffusion time regime, respectively, where the first primary peak indicates the dynamic heterogeneity stemmed from the motion of beads, and the secondary peak is the result of correlated motion along a polymer chain. Moreover, the relaxation of polymer beads shows clear two-step decay in supercooled melts and the dynamics shows growing heterogeneity with decreasing temperature. As chain length is increased, a peak of the dynamic susceptibility occurs, and the peak height,χ*4, increases and then reaches a plateau. The curves of the height of the first peak of α_2, α _2~*, versus τ and the curves of χ_4~*α versus τα follow two master curves for different chain lengths. Our results indicate the similarity of dynamic heterogeneity dominated by the motion of single bead even the chain length is different. It is interesting to find that the Stokes-Einstein(SE) relation between τα and diffusion coefficient D, D~τ-1 q, is highly length-scale dependent. The SE relation breaks down in both normal melts regime and supercooled regime at large magnitude of wave vectors, attributed to the non-Brownian motion arising from the chain connectivity and growing heterogeneity due to supercooling. However, the SE relation is reconstructed when the probing length scale is large(at small magnitude of wave vectors). Our results show a hierarchical physical picture of the supercooled polymeric dynamics.     

Compositions of nanoparticles of hexagonal symmetry

The formulas for calculation of the number of atoms in nanoparticles with symmetry group D _6h are reported. The numbers of atoms are determined by six structurally invariant numbers and the “quantum number” of the group order n. Eight classes of nanostructures with symmetry group D _6h are revealed: C _{? + 12z} , where z = 0, 1, 2, …, and C _? is C ₂, C ₆, C ₈, or C ₁₄. The sum rule for the coordination numbers of all atoms of subshells related to symmetry elements is established. Two-dimensional nanoparticles are considered.     

The Grüneisen parameter and Poisson coefficient for glassy organic polymers and inorganic glasses

The Grüneisen lattice parameter has been calculated from the data on the Poisson coefficient for amorphous polymers and glasses. For glassy polymers, the thermodynamic Grüneisen parameter characterizes anharmonicity averaged over intrachain and other vibrational modes, the Grüneisen lattice parameter defines anharmonicity of interchain interactions provided by intermolecular interactions. In the case of alkali silicate glasses, the Grüneisen lattice parameter reflects the anharmonicity of vibrations of ionic sublattice that is formed by alkali-metal ions and nonbridging oxygen atoms.     

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.     

Vanadium separation with activated carbon and iron/activated carbon nanocomposites in fixed bed column: experimental and modelling study

In this work, iron nanoparticles were impregnated onto a commercial activated carbon surface to produce a novel adsorbent called iron-activated carbon nanocomposite (I-AC). Commercial activated carbon (CAC) and I-AC were used for vanadium separation in a fixed-bed column. The effects of various operating parameters such as inlet vanadium ion concentration, adsorbent dose and volumetric flow rate on vanadium separation performance of CAC were investigated. The performance of both adsorbents was compared in three adsorption/desorption cycles. The experimental breakthrough curves of vanadium ions in the fixed-bed column were modeled using the film-pore-surface diffusion model (FPSDM). The four mass transfer parameters characterizing this model, namely the external mass-transfer coefficient (k _f ), pore and surface diffusion coefficients (D _p and D _s ), and axial dispersion coefficient (D _L ) were evaluated through the model. Modelling and experimental results showed that the I-AC nanocomposite has a better performance for vanadium separation in comparison to AC. Sensitivity analysis on the FPSDM showed that the pore and surface diffusion, external mass transfer and axial dispersion play a significant role in vanadium separation using the I-AC. On the other hand, surface diffusion resulted to be relatively less important when CAC was used.     

Supramolecular architecture of catechol and its 2:1 complex with dimethylsulfoxide

The crystal structures of catechol (o-dihydroxybenzene) and its 2:1 complex with dimethylsulfoxide are determined at T = 150 K. Crystal data: C₁₄H₁₈O₅S, M = 298.37, triclinic, space group P \(\bar 1\), unit cell parameters: a = 7.7285(13) Å, b = 9.9924(17) Å, c = 10.3188(18) Å, α = 89.963(4)°, β = 89.968(4)°, γ = 69.076(5)°, V = 744.3(2)ų, Z = 2, D _x = 1.331 g/cm³, R1 = 0.048; C₆H₆O₂, M = 110.11, monoclinic, space group P2₁/n, a = 9.8206(6)Å, b = 5.5903(3)Å, c = 10.4439(6)Å, β = 114.952(2)°; V = 519.85(5) ų, Z = 4, D _x = 1.407 g/cm³, R1 = 0.0289. In the 2:1 complex the molecules are joined in a supramolecular ensemble by D-H...A hydrogen bonds (D = O, C; A = O, π); in catechol they are bonded only by O-H...O. The state diagram of the catechol-dimethylsulfoxide system is examined by DTA.     

Quantum-chemical investigation of structure and stability of [<Emphasis Type="Italic">n</Emphasis>]-prismanes and [<Emphasis Type="Italic">n</Emphasis>]-asteranes

The study by DFT [B3LYP/6-311G(2df,p)] method of structural and energy characteristics peculiar to [n]-prismanes and [n]-asteranes demonstrated that prismanes of n = 3–10 and asteranes of n = 3–7 possessed a stable structure of D_nh-symmetry; the D_nh-geometry was distorted in the subsequent terms of the series.     

Lithium intercalation with phase transitions in model systems of electrode materials for lithium power sources

A comparison was made for Li⁺ chemical diffusion coefficients (D _Li) in graphite as calculated by mathematical models of Li⁺ intercalation under constant potential into semirestricted and restricted kinetic systems with mobile phase boundary and into a single-phase system. Close D _Li values were calculated by means of double-phase models. The double-phase model produces 6–7-fold D _Li coefficient as compared to the values of the single-phase model.     

Electron affinity and substituent effects in radical anions

The first vertical electron affinities EA of 13 series of molecules and free radicals D(X _i ) _n are related to the inductive (σ _I ), resonance (σ _R ^? ), and polarization (σ_α) parameters of substituents X _i by the dependences EA = EA _H + aΣσ _I + bΣσ _R/? + cΣσ_α: In radical anions D^+·(X _i ) _n , compared to radical cations D^+·(X _i ) _n , the polarization interaction is weaker or similar in magnitude but has an opposite sign. The previously unknown resonance parameters σ _R ^? of substituents SiMe₃ and CH₂SiMe₃ bound to the radical anion center H₂C=CH^?· were calculated.     

Nickel(II) complex with 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane

A nickel(II) complex, [Ni(taetacn)](ClO₄)₂ ? H₂O, where taetacn = 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane was synthesized. The crystal structure was determined by the single-crystal X-ray diffraction method at 293 K. The complex crystallizes in the orthorhombic space group Pna2₁ with a = 16.004(2) Å, b = 10.186(1) Å, c = 13.937(2) Å, V = 2271.9(5) ų, D_x = 1.56 g cm^?3, D_m = 1.59 g cm^?3 (floatation method), and Z = 4. The R₁ [I > 2σ(I)] and wR₂ (all data) values are 0.0636 and 0.1672, respectively, for all 4845 independent reflections. The compound is composed of octahedral nickel(II) cation with three 2-aminoethyl pendant groups of taetacn, tetrahedral ClO ₄ ^? anion, and a water molecule of crystallization. Electronic spectra are consistent with the octahedral geometry. Temperature dependence of the magnetic susceptibility (4.5–300 K) can be interpreted considering the zero-field splitting of the nickel(II) ion (g = 2.14, D = 3.72 cm^?1, and Nα = 300 × 10^?6 cm³ mol^?1). Cyclic voltammetry in DMF showed quasi-reversible and irreversible oxidation waves (E_pa = 0.54 V, E_pc = 0.45 V; E_pa = 1.16 V, E_pc = 0.71 V vs. Ag/Ag⁺).     

Calculation of the thermodynamic characteristics of ions in vapor over sodium fluoride

The geometric parameters, normal vibration frequencies, and thermochemical characteristics of the ions present in vapor over sodium fluoride, Na₂F⁺, Na₃F ₂ ⁺ , NaF ₂ ^? , and Na₂F ₃ ^? , were calculated ab initio by the Hartree-Fock method and taking into account electron correlation. The main equilibrium configuration of all ions was found to be the linear configuration of D _∞h symmetry. Pentaatomic ions could also exist as two isomers, planar cyclic of C _2v symmetry and bipyramidal of D _3h symmetry. Their energies were higher than that of the D _∞h isomers, and their contents in vapor were negligibly low. The energies and enthalpies of dissociation of the ions with the elimination of the NaF molecule were calculated. The enthalpies of formation of the ions were obtained.     

Synthesis of Block Copolymers of Styrene with <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl₄–pyridine is studied in a mixture CH₂Cl₂–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (M_n = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)₂] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (M_n = 10000–17000 g/mol) and a relatively low molecular-weight distribution (M_w/M_n = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by ¹Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.