Solvatochromic behavior of phenol blue in CO2+ethanol and CO2+n-pentane mixtures in the critical region and local composition enhancement

The UV-Vis spectra of probe phenol blue in CO(2)+ethanol and CO(2)+n-pentane binary mixtures were studied at 308.15 K and different pressures. The experiments were conducted in both supercritical region and subcritical region of the mixtures by changing the compositions of the mixed solvents. On the basis of the experimental results the local compositions of the solvents about phenol blue were estimated by neglecting the size difference of CO(2) and the cosolvents. Then the local composition data were corrected by a method proposed in this work, which is mainly based on Lennard-Jones sphere model. It was demonstrated that the local mole fraction of the cosolvents is higher than that in the bulk solution at all the experimental conditions. In the near critical region of the mixed solvents the local composition enhancement, defined as the ratio of cosolvent mole fraction about the solute to that in the bulk solution, increased significantly as pressure approached the phase boundary from high pressure. The local composition enhancement was not considerable as pressure was much higher than the critical pressure. In addition, in subcritical region the degree of composition enhancement was much smaller and was not sensitive to pressure in the entire pressure range as the concentration of the cosolvents in the mixed solvents was much higher than the concentration at the critical point of the mixtures.     

Theoretical prediction of the coordination number, local composition, and pressure-volume-temperature properties of square-well and square-shoulder fluids

By assuming a Boltzmann distribution for the molecular equilibrium between local and bulk environments, a general model is derived for the prediction of coordination numbers and local compositions of square-well and square-shoulder fluids. The model has no empirical parameter fitted from the data of square-well and square-shoulder fluids, but is valid from the low-density limit to the high-density limit. The applicable width of well or shoulder covers the commonly used range varying from 1.0 to 2.0. The model can accurately predict the coordination numbers of pure square-well and square-shoulder fluids, so the equation of state derived from it is superior to other equations of state based on the existing coordination number models. The model also accurately predicts the local compositions of mixtures in wide ranges of density and size ratio (1.0-8.0), as well as the configuration energy of lattice gases and highly nonideal lattice mixtures. It is remarkable that the model correctly predicts temperature-dependent coordination numbers and local compositions for both equal- and unequal-sized mixtures at close packing, which cannot be predicted by the existing coordination number models. Our derivation demonstrates that the energy parameters in local composition models should represent the potential difference of a molecule between the local and bulk environments, not the pair-interaction potential, and depend on the system conditions and different kinds of pair-interaction parameters. This result is very useful for the development of local composition and activity coefficient models and the mixing rules of equations of state.     

Recycling of polymer waste: Part 1—Photo-oxidized polypropylene

In order to recycle photo-oxidized polypropylene, blends of this polymer waste with virgin polypropylene have been prepared with different compositions.Both rheological and mechanical properties depend on composition. Rheological properties indicate some interactions between the two polymers at low shear rates. On the other hand, at high shear rates there is evidence of incompatibility.The nominal tensile strength is almost independent of the composition, while the other mechanical properties are similar to those of the degraded material up to a virgin PP content of about 75%, after which they quickly reach the values for the virgin polypropylene.These features are correlated with the large spherulite size of these blends.     

Modeling the morphology and mechanical properties of sheared ternary mixtures

Through a combination of simulation techniques, we determine both the structural evolution and mechanical properties of blends formed from immiscible ternary mixtures. In this approach, we first use the lattice Boltzmann method to simulate the phase separation dynamics of A/B/C fluid mixtures for varying compositions within the spinodal region. We also investigate the effect of an imposed shear on the phase ordering of the mixture. We assume that the fluid is quenched sufficiently rapidly that the phase-separated structure is preserved in the resultant solid. Then, the output from our morphological studies serves as the input to the lattice spring model, which is used to simulate the elastic response of solids to an applied deformation. These simulations reveal how the local stress and strain fields and the global Young's modulus depend on the composition of the blend and the stiffness of the components. By comparing the results for the sheared and unsheared cases, we can isolate optimal processing conditions for enhancing the mechanical performance of the blends. Overall, the findings provide fundamental insight into the relationship between structure, processing, and properties for heterogeneous materials and can yield guidelines for formulating blends with the desired macroscopic mechanical behavior.     

Influence of block composition on crack toughness behaviour of styrene-b-(styrene-random-butadiene)-b-styrene triblock copolymers

The deformation and fracture behaviour of symmetric and asymmetric styrene-b-(styrene-random-butadiene)-b-styrene (S-SB-S) triblock copolymers with variations in their molecular architectures in terms of their outer PS block and the random SB middle block composition ratios have been investigated using essential work of fracture approach based on post yield fracture mechanics concept. The present investigations on crack resistance behaviour of these S-(S/B)-S triblock copolymers where effective interaction parameter (χ_eff) is systematically varied through the variation of block compositions and architecture is in continuation to our earlier communicated short article highlighting the phase behaviour-morphology and mechanical property interrelation. The crack initiation and propagation behaviours are correlated to morphology and dynamic mechanical properties as obtained from TEM, SAXS and DMA measurements. The influence of interaction parameter (χ-parameter) space which has been manipulated through the variation of block compositions has clearly manifested in their morphologies and in their mechanical properties. Further the kinetic aspects of fracture mechanical response have also been investigated where all the materials have clearly revealed block composition dependence. SEM analysis was carried out to understand the fracture modes prior to failure.     

Application of a new equation of state to liquid refrigerant mixtures

A new general equation of state recently reported for pure liquids has been developed to predict the volumetric and thermodynamic properties of six binary and two ternary liquid refrigerant mixtures (including HCs and HFCs mixtures) at different temperatures, pressures, and compositions. The results show this equation of state can be used to reproduce and predict different thermodynamic properties of liquid refrigerant mixtures within experimental errors. The composition dependence of the parameters of this equation of state has been assumed as quadratic functions of mole fraction. Using these mixing rules, the agreement between calculated and experimental densities is better than 0.6% for binary mixtures and 2.3% for ternary mixtures. To compare the performance of this new equation of state against other well-known methods such as the COSTALD method, the density of some refrigerant mixtures, for which the parameters of COSTALD were available, has been computed and compared with those of this new equation of state.     

The effect of composition drift and copolymer microstructure on mechanical bulk properties of styrene-methyl acrylate emulsion copolymers

In order to determine the influence of composition drift and copolymer microstructure on the mechanical bulk properties of styrene -methyl acrylate copolymers, several copolymers were produced by emulsion copolymerization. Three different average compositions were used. By performing the copolymerizations under batch and semicontinuous conditions with two different monomer addition strategies (starved conditions and optimal addition) it was possible to control composition drift and to produce copolymers with different microstructures (chemical composition distributions). All these copolymers were processed in a way that ensured that the original particle structure was lost before the polymers were tested. It was found that composition drift had an influence on the mechanical properties (Young's modulus, maximum stress, elongation at break). This influence could be understood very well on the basis of present knowledge about structure-mechanical properties relationships. In the case of homogeneous copolymers maximum stress and elongation at break are dependent on the molecular weight, and only weakly dependent on the chemical composition, and Young's modulus is independent of chemical composition and molecular weight in the range of compositions investigated, as expected. In the case of heterogeneous copolymers, the influence of copolymer microstructure on Young's modulus, maximum stress and elongation at break is very large. Depending on the extent of control of composition drift during the polymerizations, phase separation was observed in the processed polymers, and the presence of a rubber phase affected the properties profoundly.     

The generalized van der Waals partition function. III. Local composition models for a mixture of equal size square-well molecules

New local composition models for mixtures of equal size molecules with differing attractive forces are presented, and compared with our results of Monte Carlo computer simulations for mixtures of square-well molecules which are also reported here. Unlike most previous local composition models, these new models predict random mixing in the high density limit and Boltzmann factor nonrandomness at low density; both limiting behaviors are in agreement with statistical mechanical theory. The predictions of these new models as a function of composition, density and temperature are in good agreement with the Monte Carlo computer simulation results.     

Local and global properties of mixtures in one-dimensional systems. Part I. Mixtures of two simple components

Two sets of quantities are calculated for two-component mixtures in one dimension. One consists of the traditional excess thermodynamic quantities which provide global information on the mixtures. The second, referred to as local properties, consists of the Kirkwood-Buff integrals, local composition, solvation, and preferential solvation quantities. In this part, we discuss simple particles interacting via either square-well potential or hard rod potential. It is shown that a host of new information can be obtained from the local properties of the mixtures which supplements the information conveyed by the global properties.     

Excess enthalpies and (vapour + liquid) equilibrium data for the binary mixtures of dimethylsulphoxide with ketones

Excess enthalpies (H^E), at ambient pressure and T = 298.15 K, have been measured by using a solution calorimeter for the binary liquid mixtures of dimethyl sulphoxide (DMSO) with ketones, as a function of composition. The ketones chosen in the present investigation were methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone (CH). The H^E values are positive over the entire composition range for the three binary mixtures. Furthermore, the (vapour + liquid) equilibrium (VLE) was measured at 715 Torr for these mixtures, of different compositions, with the help of Swietoslawski-ebulliometer. The experimental temperature-mole fraction (t-x) data were used to compute Wilson parameters and then used to calculate the equilibrium vapour-phase compositions as well as the theoretical points for these binary mixtures. These Wilson parameters are used to calculate activity coefficients (γ) and these in turn to calculate excess Gibbs free energy (G^E). The intermolecular interactions and structural effects were analyzed on the basis of the measured and derived properties.     

Preferential Solvation of Some Sulfonamides in Propylene Glycol + Water Solvent Mixtures According to the IKBI and QLQC Methods

The preferential solvation parameters, which represent differences between the local and bulk mole fractions of the solvents near to the solute, in solutions of some sulfonamides in propylene glycol + water binary mixtures are derived from their thermodynamic properties by means of the inverse Kirkwood?Buff integrals (IKBI) and the Quasi-Lattice Quasi-Chemical (QLQC) method. From solvent effect studies, it is found that sulfonamides are sensitive to solvation effects; the preferential solvation parameter, δx _PG,S, is negative in water-rich mixtures but positive in compositions from 0.20 to 1.00 in mole fraction of propylene glycol according to IKBI method and positive in all co-solvent compositions if the QLQC method is considered. It is conjecturable that in water-rich mixtures, hydrophobic hydration around the aromatic ring and/or other non-polar groups plays a relevant role in the solvation. The greater solvation by propylene glycol mixtures of similar solvent compositions and in co-solvent-rich mixtures could be due mainly to polarity effects and acidic behavior of the sulfonamides, in contrast to the more basic solvent propylene glycol.     

Preferential hydration of lysozyme in water/glycerol mixtures: a small-angle neutron scattering study

In solution small-angle neutron scattering has been used to study the solvation properties of lysozyme dissolved in water/glycerol mixtures. To detect the characteristics of the protein-solvent interface, 35 different experimental conditions (i.e., protein concentration, water/glycerol fraction in the solvent, content of deuterated compounds) have been considered and a suitable software has been developed to fit simultaneously the whole set of scattering data. The average composition of the solvent in the close vicinity of the protein surface at each experimental condition has been derived. In all the investigated conditions, glycerol resulted especially excluded from the protein surface, confirming that lysozyme is preferentially hydrated. By considering a thermodynamic hydration model based on an equilibrium exchange between water and glycerol from the solvation layer to the bulk, the preferential binding coefficient and the excess solvation number have been estimated. Results were compared with data previously derived for ribonuclease A in the same mixed solvent: even if the investigated solvent compositions were very different, the agreement between data is noticeable, suggesting that a unique mechanism presides over the preferential hydration process. Moreover, the curve describing the excess solvation number as a function of the solvent composition shows the occurrence of a region of maximal hydration, which probably accounts for the changes in protein stability detected in the presence of cosolvents.     

Phase separation kinetics in mixtures of polymers and liquid crystals

Light scattering has been used to study phase separation kinetics in mixtures containing liquid crystals and epoxy resins. In the samples studied, phase separation was induced by the polymerization of the resins with an appropriate curing agent. Experiments were carried out at different compositions and at different temperatures. The results show that the kinetic mechanism of phase separation is composition dependent. For high liquid crystal content the data are in qualitative agreement with existing theories describing spinodal decomposition; at lower concentrations the mechanism is different. The physical properties of the resulting materials are independent of the decomposition mechanism. The data have also been analysed considering the scaling behaviour expected for late stages of phase separation in polyinduced meric mixtures. Samples obtained in a narrow concentration range, where the two kinetic mechanisms overlap, exhibit peculiar physical properties.     

Ultrasound speeds and molar isentropic compressions of (3-ethoxypropane-1-amine + water) mixtures from T = (283.15 to 303.15) K

Alkoxyamines containing two hydrophilic groups with great affinity to water are multipurpose compounds with important applications, either on theoretical or practical grounds. The thermodynamic characterization of aqueous mixtures of these compounds is scant. Ultrasound speed measurements have been made in 53 mixtures of the aqueous ethoxypropane-1-amine binary system, across the entire composition range and temperatures between T = (283.15 and 303.15) K, at atmospheric pressure. By combining ultrasound speed and density data, values of the isentropic compressibility were derived. Excess molar isentropic compressions were estimated and analytically fitted to Redlich–Kister polynomial equations. Excess partial molar quantities were then calculated including their limiting values, which were obtained from the Redlich–Kister fitting coefficients. The temperature dependences of limiting partial molar isentropic compressions and isobaric expansions were also scrutinized. Compressibility changes associated with different patterns of aggregation and hydration over the whole composition range are identified.     

A note on excess Gibbs energy models,equations of state and the local composition concept

A density-dependent local composition expression for the residual energy is derived from a generalized NRTL expression for the excess energy and the van der Waals fluid theory. Integration of this expression yields a volume-dependent expression for the Helmholtz energy from which equations of state utilizing the local composition concept are derived and which in the high-density limit contain the well-known activity coefficient models.The local composition versions of the Carnahan—Starling—van der Waals, the Redlich—Kwong—Soave and the Peng—Robinson equations of state are derived. It is further shown that the group contribution versions of the NRTL, the Wilson and the UNIQUAC excess models may be derived from the generalized NRTL expression for the residual energy when applied to groups instead of molecules.It is thus demonstrated that all current local composition activity-coefficient models can be derived from a local composition version of the van der Waals equation of state using different sets of assumptions. In the same way the van Laar, the Scatchard—Hildebrand and the Flory—Huggins activity coefficient models are obtained from the van der Waals equation of state using the original mixing rules.     

二元复杂共混体系组成的SEC-LS分析

提供了一种利用体积排阻色谱-光散射(SEC-LS)联用技术来解决二元复杂共混体系组成的定量分析问题.基于体积排除色谱的绝对定量化原则,首先从理论上分析了共混物的光散射响应因子与组成呈线性关系.通过分析六组复杂共混体系的光散射响应因子与组成的关系,验证了该线性关系确实存在.进而利用该线性关系计算了共混体系的组成.在某些共混体系中,通过光散射响应因子得出的组成比利用示差法得出的组成更加接近原料组成.通过分析这两种方法产生误差的来源,阐述了产生该现象的原因.     

A Kirkwood-Buff analysis of local properties of solutions

For decades, the properties of liquid mixtures have been analyzed in terms of excess thermodynamic functions. These functions convey global or macroscopic information on the system. In this work, a complementary view, based on the local properties of the same system is suggested. These properties are richer and more informative regarding the local densities, composition and solvation effect. A few examples ranging from Lennard-Jones particles, to inert gas mixtures, to aqueous solutions are presented, stressing the local information that cannot be obtained directly from global properties.     

A new force field model of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and acetonitrile mixtures

Recently, we introduced a new force field (FF) to simulate transport properties of imidazolium-based room-temperature ionic liquids (RTILs) using a solid physical background. In the present work, we apply this FF to derive thermodynamic, structure, and transport properties of the mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF(4)], and acetonitrile (ACN) over the whole composition range. Three approaches to derive a force field are formulated based on different treatments of the ion-ion and ion-molecule Coulomb interactions: unit-charge, scaled-charge and floating-charge approaches. The simulation results are justified with the help of experimental data on specific density and shear viscosity for these mixtures. We find that a phenomenological account (particularly, a simple scaled-charge model) of electronic polarization leads to the best-performing model. Remarkably, its validity does not depend on the molar fraction of [BMIM][BF(4)] in the mixture. The derived FF is so far the first molecular model which is able to simulate all transport properties of the mixtures, comprising RTIL and ACN, fully realistically.     

True reactivity ratios for styrene-methyl methacrylate copolymerization in bulk

The local composition concept has been adopted to account for the monomer partitioning effect in the vicinity of the growing macroradical in radical copolymerization. Local compositions were calculated in a two step procedure. In the first step the activity coefficients were calculated in the assumed model systems using the UNIFAC group contribution method

1 UNIFAC means UNIQUAC Functional Group Activity Coefficients, where UNIQUAC stands for Universal Quasichemical Activity Coefficients.

. Subsequently, the modified Wilson equation was applied for estimation of the Boltzmann factor in the derived formulae. Terminal and penultimate models for the bulk copolymerization were investigated. For both models corresponding formulae were derived relating copolymer composition with local mole fractions and the true reactivity ratios. Test calculations have been performed for the bulk styrene-methyl methacrylate system at 313.15 K.