Fragments of the coherent phase diagram and the kinetics of growth of elastically strained layers of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te solid solutions

The influence of the elastic component of the Gibbs energy of mixing on phase formation in the Cd-Hg-Te system was studied by a comparison of calculated dependences of layer parameters on growth conditions performed with and without the inclusion of mechanical strains in the growth system. The appearance of elastic strains between a layer and a substrate of the initial binary compounds insignificantly decreased the growth rate and almost did not influence the composition of the growing layer. The approximation of coherent conjugation of phases in the presence of elastic strain in the system and the assumption of the existence of chemical phase equilibrium at the interphase boundary give similar results for material growth. Both approaches quite satisfactorily describe the experimental data on layer growth under various temperature-time conditions.     

Excess Gibbs Energy of Mixing for Organic Carbonates from Fitting of Their Binary Phase Diagrams with Nonideal Solution Models

The excess Gibbs energies of mixing in the liquid state were evaluated for all the ten binary combinations of these five organic carbonates: ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate, and diethyl carbonate by fitting their measured binary phase diagrams with thermodynamic nonideal solution models based on the regular solution model. Using the results of these model fits, activity coefficients of the components in the solvent mixtures were calculated for the binary series containing EC and DMC as the common component, and the composition-averaged excess Gibbs energies of mixing were calculated by integrating the energy in the whole composition range for all the binaries. The results showed the excess Gibbs energy of mixing, and therefore the intermolecular forces, to be responsible for the changes in the phase diagrams, in the activity coefficients, and in the composition-averaged excess energy for the different binary solution combinations.     

Mixing rules for binary Lennard–Jones chains: theory and Monte Carlo simulation

Theoretically-based van der Waals one-fluid (vdW1) mixing rules are derived for Lennard–Jones (LJ) chain mixtures. The rules provide equivalent one-fluid segment parameters for LJ size (σ) and energy () parameter as well as chain length (m) based on the parameters of the individual mixture components and the component mole fractions. The mixing rules are tested by performing Monte Carlo simulations of eight different binary mixtures and the equivalent vdW1 pure fluid, each at three densities. The simulations test the effects of changing LJ size parameter, LJ energy parameter and chain length individually and together. The effects of mole fraction and density are also examined. The mixing rules are tested for accuracy in predicting compressibility factors and radial distribution functions. It is found that the vdW1 rules provide excellent agreement when size and energy parameter are varied. Good agreement is found for mixtures with different chain lengths. The discrepancy is worst at very high densities when all component parameters are varied simultaneously.     

Structural-thermodynamic characteristics and intermolecular interactions in mixtures of strongly associated solvents with aprotic amides

Thermodynamic characteristics of mixtures of aprotic amides with water and organic solvents with hydrogen bond networks are calculated. Within a model approach the specific and non-specific components of the total energy of the intermolecular interaction are determined, based on which the corresponding contributions to the enthalpies of component mixing are calculated. It is found that negative enthalpies of mixing in the mixtures under study are due to non-specific interactions rather than heterocomponent specific ones. It is shown that the difference in the structural-thermodynamic characteristics of aqueous and nonaqueous mixtures of aprotic amides is mainly caused by packing features of solutions and the behavior of hydrogen bond networks of water and organic solvents.     

Regular solution model as applied to the interaction of halides in melt

Binary solid-liquid phase diagrams of halides with a common anion and a known mixing energy of the components in melt are analyzed by the regular solution model. The solid-liquid phase diagrams of eutectic systems with a negative mixing energy of molten components (i.e., systems with complex formation in melt) are satisfactorily fitted by this model.     

Compatibility of coils and rods bearing flexible side chains

We present a theoretical treatment of nematic-isotropic phase equilibria in mixtures which consist of random coils and comblike polymers, the latter components being composed of a rigid backbone and flexible side chains. The mixing partition function is evaluated by using the Flory lattice model. The comblike component is characterized by the axial ratio x_r of its rigid main chain and the number of flexible side chains z, each containing m segments. The coiled component is described by its number of segments x_c. The net exchange energy of mixing is assumed to be zero; i.e., we consider athermal solutions. It is shown that the flexible side chains attached to the rigid main chains markedly enhance the compatibility in the isotropic phase. If the ratio of the volume fraction of the side chains to the volume fraction of the main chains is high enough, there is even a finite range of concentration where the random coils mix homogeneously with the comblike component. This is in contrast to mixtures of rods and coils, which have been shown by Flory to be incompatible over nearly the full range of composition. These conclusions hold true only when ordered states are involved. For comblike polymers with flexible backbones mixed with random coils in isotropic melts, the resulting free energy of mixing is given by the familiar Flory-Huggins expression.     

A transport model for swelling of polyelectrolyte gels in simple and complex geometries

A model for the swelling of polyelectrolyte gels in salt solutions is developed and solved numerically. The model accounts for the effect of network stress, osmotic pressure, and electrical potential on the species diffusive flux. The osmotic pressure and the network stress are derived from the Helmholtz free energy of the system that is the sum of mixing, elastic, and electrostatic components. One- and two-dimensional swelling in unconstrained and constrained geometries are simulated for a salt–solvent–polymer system. The transient and equilibrium fields of electrical potential, concentrations, deformation, and stress are obtained. Transient overshoots and non-uniformities in the residual profiles are predicted.     

Comparison of different mixing rules for prediction of density and residual internal energy of binary and ternary Lennard–Jones mixtures

Mixing rules are necessary when equations of state for pure fluids are used to calculate various thermodynamic properties of fluid mixtures. The well-known van der Waals one-fluid (vdW1) mixing rules are proved to be good ones and widely used in different equations of state. But vdW1 mixing rules are valid only when molecular size differences of components in a mixture are not very large. The vdW1 type density-dependent mixing rule proposed by Chen et al. [1] is superior for the prediction of pressure and vapor–liquid equilibria when components in the mixture have very different sizes. The extension of the mixing rule to chain-like molecules and heterosegment molecules was also made with good results. In this paper, the comparison of different mixing rules are carried out further for the prediction of the density and the residual internal energy for binary and ternary Lennard–Jones (LJ) mixtures with different molecular sizes and different molecular interaction energy parameters. The results show that the significant improvement for the prediction of densities is achieved with the new mixing rule [1], and that the modification of the mixing rule for the interaction energy parameter is also necessary for better prediction of the residual internal energy.     

Construction of the free energy landscape of biomolecules via dihedral angle principal component analysis

A systematic approach to construct a low-dimensional free energy landscape from a classical molecular dynamics (MD) simulation is presented. The approach is based on the recently proposed dihedral angle principal component analysis (dPCA), which avoids artifacts due to the mixing of internal and overall motions in Cartesian coordinates and circumvents problems associated with the circularity of angular variables. Requiring that the energy landscape reproduces the correct number, energy, and location of the system's metastable states and barriers, the dimensionality of the free energy landscape (i.e., the number of essential components) is obtained. This dimensionality can be determined from the distribution and autocorrelation of the principal components. By performing an 800 ns MD simulation of the folding of hepta-alanine in explicit water and using geometric and kinetic clustering techniques, it is shown that a five-dimensional dPCA energy landscape is a suitable and accurate representation of the full-dimensional landscape. In the second step, the dPCA energy landscape can be employed (e.g., in a Langevin simulation) to facilitate a detailed investigation of biomolecular dynamics in low dimensions. Finally, several ways to visualize the multidimensional energy landscape are discussed.     

Flux d'énergie d'un écoulement de Poiseuille vers la paroi d'un tube élastique,a. Modes d'instabilité axisymétrique

Ne compute the energy flux from a fluid flowing to an elastic hollow cylindrical tube generated by unstable modes. The basic fluid velocity flow is the parabolic Hagen-Poiseuille flow. We show that the energy flux from the fluid flowing to the elastic wall is positive when the mode is unstable, negative when the mode is stable, and null when the mode is neutral. Moreover the energy flux from the fluid flowing to the elastic solid is generated by the component of the force perpendicular to the wall at the interface for high Reynolds numbers, and essentially by the streamwise component of the force at interface for low Reynolds numbers.     

Isobaric vapour–liquid equilibria of methyl cellosolve–aliphatic alcohol systems

Isobaric vapour–liquid equilibrium data are determined at 40 and 95 kPa for six binary mixtures consisting of methyl cellosolve (2-methoxyethanol) as a common component and aliphatic alcohols as non-common components. The non-common components include ethanol, 1-propanol, 1-butanol, 2-methyl 1-propanol, 2-methyl 2-propanol and 1-pentanol. The experimental T–x data are correlated using Wilson and NRTL equations for the liquid phase activity coefficients using a non-linear regression approach based on maximum likelihood principle. Excess free energy of mixing, computed from the activity coefficients, is positive in all the systems over the entire range of composition.     

Dispersive mixing in immiscible polymer blends

Dispersive mixing of immiscible polymer blends as well as polymer systems containing solids is achieved in compounding equipment at two stages of the system's processing experience: first, while one or more of the polymer components are melting, and second, after all polymer components have melted. That is, the first mode of dispersive mixing occurs during the melting mechanism of “dissipative mix melting” (Ref. 1), while the second is melt-melt mixing. During the compounding of a given blend system, there are a number of processing parameters that can be changed in order to improve mixing. These range from machine operating variables to the addition of processing aids. If such processing changes fail to produce the desired morphology, the most common change to consider is the screw geometry. This, in practice involves a trial and error procedure, or the use of an existing database built from prior experience. The role which the thermomechanical and rheological properties of the blend component play in dissipative mix melting and melt-melt mixing has not yet been well understood. The reason for this is that although most blend systems have components which are strongly non-Newtonian and strongly viscoelastic, the thinking and rules of thumb for mixing such materials has been heavily influenced by the analysis of G. I. Taylor (Ref. 2), who in 1932 addressed the phenomenon of the dispersion of a single Newtonian droplet by a Newtonian matrix flowing in laminar shear flow. This paper addresses the strong role that the rheology of blend components, under processing conditions, play in laminar dispersive mixing of polymer blends. From a practical point of view, if the dispersion mechanisms and rates of dispersion depend on the component rheology, then such knowledge can lead us to the selection of advantageous mixing element designs and processing conditions. The experimental results were obtained in dispersive mixing carried out in devices developed in the Polymer Mixing Study (Ref. 3). Such model devices include the Couette Flow Intensive Mixer (CIM) (Ref. 4), where a constant shear stress is applied on the blend components and the Twin Screw Mixing Element Evaluator (TSMEE) (Ref. 5), where the mixing flows are those encountered in actual mixing/compounding operations. The TSMEE will be described in the body of this paper together with its on- and off-line morphology determination capabilities and its in-line rheology sensor. The low-density polyethylene (LDPE) and polystyrene (PS) polymers studied were selected because they cover a wide spectrum of rheological properties.     

Correlation and prediction of ternary excess enthalpy data

Methods for predicting ternary excess enthalpies from excess enthalpy data for the three binary mixtures involved are examined and tested for forty-two sets of ternary data. In order to study the relation between the performance of the methods and the characteristics of the components in the mixture, the sets of data were classified into four groups according to the chemical nature of their components. The asymmetric equations proposed by Scatchard, Toop, and Hillert are shown to provide accurate predictions. The ratio of the standard deviations between experimental and predicted excess enthalpies and the maximum absolute value of this magnitude is 0.05 or less for most of the systems. These equations are asymmetric with respect to the numbering of components. A rule is given for selecting which component is to be designated as component 1 for systems showing endothermic mixing, exothermic mixing, or a combination of endothermic and exothermic mixing. Correlation methods are also examined and a partial differential approximant is proposed to represent the ternary contribution to the excess enthalpy.     

Morphology,surface roughness,electron inelastic and quasielastic scattering in elastic peak electron spectroscopy of polymers

In elastic peak electron spectroscopy (EPES), the nearest vicinity of elastic peak in the low kinetic energy region reflects electron inelastic and quasielastic processes. Incident electrons produce surface excitations, inducing surface plasmons, with the corresponding loss peaks separated by 1–20 eV energy from the elastic peak. In this work, X‐ray photoelectron spectroscopy (XPS) and helium pycnometry are applied for determining surface atomic composition and bulk density, whereas atomic force microscopy (AFM) is applied for determining surface morphology and roughness. The component due to electron recoil on hydrogen atoms can be observed in EPES spectra for selected primary electron energies. Simulations of EPES predict a larger contribution of the hydrogen component than observed experimentally, where hydrogen deficiency is observed. Elastic peak intensity is influenced more strongly by surface morphology (roughness and porosity) than by surface excitations and quasielastic scattering of electrons by hydrogen atoms. Copyright © 2007 John Wiley & Sons, Ltd.     

Simultaneous light emission from a mixture of dendrimer encapsulated chromophores: a model for single-layer multichromophoric organic light-emitting diodes

The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device.     

Effect of Ester Moiety on Structural Properties of Binary Mixed Monolayers of Alpha-Tocopherol Derivatives with DPPC

Phospholipid membranes are ubiquitous components of cells involved in physiological processes; thus, knowledge regarding their interactions with other molecules, including tocopherol ester derivatives, is of great importance. The surface pressure–area isotherms of pure α-tocopherol (Toc) and its derivatives (oxalate (OT), malonate (MT), succinate (ST), and carbo analog (CT)) were studied in Langmuir monolayers in order to evaluate phase formation, compressibility, packing, and ordering. The isotherms and compressibility results indicate that, under pressure, the ester derivatives and CT are able to form two-dimensional liquid-condensed (LC) ordered structures with collapse pressures ranging from 27 mN/m for CT to 44 mN/m for OT. Next, the effect of length of ester moiety on the surface behavior of DPPC/Toc derivatives’ binary monolayers at air–water interface was investigated. The average molecular area, elastic modulus, compressibility, and miscibility were calculated as a function of molar fraction of derivatives. Increasing the presence of Toc derivatives in DPPC monolayer induces expansion of isotherms, increased monolayer elasticity, interrupted packing, and lowered ordering in monolayer, leading to its fluidization. Decreasing collapse pressure with increasing molar ratio of derivatives indicates on the miscibility of Toc esters in DPPC monolayer. The interactions between components were analyzed using additivity rule and thermodynamic calculations of excess and total Gibbs energy of mixing. Calculated excess area and Gibbs energy indicated repulsion between components, confirming their partial mixing. In summary, the mechanism of the observed phenomena is mainly connected with interactions of ionized carboxyl groups of ester moieties with DPPC headgroup moieties where formed conformations perturb alignment of acyl chains, resulting in increasing mean area per molecule, leading to disordering and fluidization of mixed monolayer.     

Molecular-dynamics studies of binary mixtures of Lennard-Jones fluids with differing component sizes

Molecular-dynamics calculations have been carried out for six pure liquids and three binary mixtures of Lennard-Jones fluids with differing component sizes and attractive interactions. Internal energies, radial-distribution functions, velocity autocorrelation functions and self-diffusion coefficients have been calculated and are discussed together with our previous results. The three mixtures obey the Lorentz-Berthelot rules and show endothermic mixing. The excess internal energy ΔU^E of mixtures with equal-sized components is symmetrical with respect to the mole fraction, but those for mixtures of different-sized components become asymmetrical. A comparison is made between the present ΔU^E data and those for real mixtures.     

Effects of Calcium Ions on Thermodynamic Properties of Mixed Bilirubin/Cholesterol Monolayers

The mixed monolayer behavior of bilirubin/cholesterol was studied through surface pressure-area (?-A) isotherms on aqueous solutions containing various concentrations of calcium ions. Based on the data of ?-A isotherms, the mean area per molecule, collapse pressure, surface compressibility modulus, excess molecular areas, free energy of mixing, and excess free energy of mixing of the monolayers on different subphases were calculated. The results show an expansion in the structure of the mixed monolayer with Ca2+ in subphase, and non-ideal mixing of the components at the air/water interface is observed with positive deviation from the additivity rule in the excess molecular areas. The miscibility between the components is weakened with the increase of concentration of Ca2+ in subphase. The facts indicate the presence of coordination between Ca2+ and the two components. The mixed monolayer, in which the molar ratio of bilirubin to cholesterol is 3:2, is more stable from a thermodynamic point of view on pure water. But the stable 3:2 stoichiometry complex is destroyed with the increase of the concentration of Ca2+ in subphase. Otherwise, the mixed monolayers have more thermodynamic stability at lower surface pressure on Ca2+ subphase.     

超额自由能型汽液相平衡混合规则

较全面地介绍了近几年来发展的各种典型的超额自由能型汽液相平衡混合规则。该类混合规则吸取了状态方程法和活度系数法在相平衡预测方面的优点,并将对于极性体系预测能力非常强的活度系数模型直接应用于状态方程法的相平衡预测中,实现了向高温区的良好外推和对超临界和亚临界组分的连续准确描述。依次发展的HV型、WS型和TC型三个大类的超额自由能型混合规则中,TC型混合规则的预测精确度要略高于HV型、WS型混合规则的预测精确度,而HV型、WS型混合规则的预测精确度大致相当。从发展的角度看,这些超额自由能型混合规则还要接受三元以上体系的汽液相平衡和液液相平衡预测的考验。另外,如何将超额自由能型混合规则扩展到多参数方程来提高相平衡预测精度,也是超额自由能型混合规则的一个值得关注的发展方向。     

Biodegradable systems: Thermodynamics, rheological properties, and biocorrosion

Systems based on starch and chitosan blends with synthetic polymers and cellulose derivatives (poly(ethylene oxide) and methyl cellulose of various molecular masses, PA, and ethylene-vinyl acetate copolymers containing different amounts of vinyl acetate groups) have been studied. The thermodynamic characteristics of the formation of blends have been determined. The rheological properties characterizing formation of blends from melts have been investigated. The biocorrosion ability of the blends after their use has been estimated by various methods. The concentration dependences of the thermodynamic functions of mixing of components (change in the Gibbs energy, enthalpy, and entropy) change sign in a wide composition range, indicating the complexity of mixing of rigid-chain natural polysaccharides with synthetic polymers. The rheological study of blends in which starch or chitosan plays the role of a biodegradation modifier shows that they are non-Newtonian fluids. The absolute values of viscosity and the activation parameters of melts increase with the content of polysaccharide in the system. The values of viscosity correspond to those typical for commercially processable polymers. The blends under study are biodegradable in a wet and water-soil medium with the content of the natural component being in the range 15–30 wt %.