Phase behavior of binary symmetric mixtures in pillared slit-like pores: a density functional approach

Density functional approach is applied to study the phase behavior of symmetric binary Lennard-Jones(12,6) mixtures in pillared slit-like pores. Our focus is in the evaluation of the first-order phase transitions in adsorbed phases and lines delimiting mixed and demixed adsorbed phases. The scenario of phase changes is sensitive to the pore width, to the energy of fluid-solid interaction, the amount, and the length of the pillars. Quantitative trends and qualitative changes of the phase diagrams topology are examined depending on the values of these parameters. The presence of pillars provides additional excluded volume effects, besides the confinement due to the pore walls. The effects of attraction between fluid species and pillars counteract this additional confinement. We have observed that both the increasing surface pillar density and the augmenting strength of fluid-solid interactions can qualitatively change the phase diagrams topology for the model with sufficiently strong trends for demixing. If the length of pillars is sufficiently large comparing to the pore width at low temperatures, we observe additional phase transitions of the first and second order due to the symmetry breaking of the distribution of chain segments and fluid species with respect to the slit-like pore center. Re-entrant symmetry changes and additional critical points then are observed.     

Rescaled density expansions and demixing in hard-sphere binary mixtures

The demixing transition of a binary fluid mixture of additive hard spheres is analyzed for different size asymmetries by starting from the exact low-density expansion of the pressure. Already within the second virial approximation the fluid separates into two phases of different composition with a lower consolute critical point. By successively incorporating the third, fourth, and fifth virial coefficients, the critical consolute point moves to higher values of the pressure and to lower values of the partial number fraction of the large spheres. When the exact low-density expansion of the pressure is rescaled to higher densities as in the Percus-Yevick theory, by adding more exact virial coefficients a different qualitative movement of the critical consolute point in the phase diagram is found. It is argued that the Percus-Yevick factor appearing in many empirical equations of state for the mixture has a deep influence on the location of the critical consolute point, so that the resulting phase diagram for a prescribed equation has to be taken with caution.     

2D-SAFT-VR approach to study of the adsorption isotherms for binary mixtures

In this article we present results of approximating molecular modeling of the gas mixtures methane-nitrogen, methane-carbon dioxide, and nitrogen-carbon dioxide adsorbed on activated carbon at a temperature of 318.2 K, based on the Statistical Associating Fluid Theory for potentials of Variable Range. Unlike the previous work (Castro et al.) showing the results in rescaled units, in this work the results obtained are shown in real units as obtained in the experiments.     

Internal pressure and cohesive energy density for binary non-electrolyte mixtures

Internal pressures and cohesive energy densities of binary liquid mixtures of n-pentane+dichloromethane, n-pentane+methylacetate, 2-propanol+methylacetate and n-bytylamine+1,4-dioxane at 25°C have been evaluated from molar volumes surface tensions and enthalpies. The data obtained provide information about interactions in the binary liquid mixtures which can be correlated with results from other thermodynamic properties.Presented at the VI Congreso Argentino de Fisicoquímica, Santiago del Estero, Argentina, 1989.     

Scaling function of critical binary mixtures: Nitrobenzene-n-hexane data revisited

Ultrasonic attenuation spectra of the nitrobenzene-n-hexane mixture of critical composition have been analysed. Data between 50 kHz and 1 GHz from different sources have been included to show that at a given temperature the spectra, in addition to the critical contribution, reveal a non-critical relaxation term. Taking this additional term into account inconsistencies in the scaling function reported in the literature are avoided. In the final analysis the scaling function of the nitrobenzene-n-hexane system follows the predictions of the Bhattacharjee-Ferrell theory with critical amplitude and relaxation rate of concentration fluctuations in nice agreement with determinations from independent methods. The low-frequency attenuation data are briefly discussed with a view to a bulk viscosity approach which yields a slightly different proportionality constant in the linear regime of the scaling function than the Bhattacharjee-Ferrell theory. Evidence in favour of the latter is obtained.     

Raoult's law as applied to binary solvent mixtures

The inapplicability of the original statement of Raoult's law to binary solvent mixtures has been known for many years. An appropriate form for binary solvent mixtures is developed from the fundamental thermodynamic concept of fugacity, and is shown to be quantitatively applicable to the water+tetrahydrofuran solvent system and qualitatively applicable to the results which have been obtained for other aqueous organic solvent mixtures.     

A new approach to explain concentration-dependent changes of isotropic Raman line width in the associated binary mixtures

We report on a new empirical relationship to explain the concentration-dependent isotropic Raman line width changes of a vibrational mode in uniform binary mixtures. The factors contributing to the intrinsic line width and several other broadening mechanisms are, in general, concentration-dependent. Concentration fluctuation in a microscopic volume and microviscosity are the two factors that are known to cause a concentration-dependent line width variation. These two factors combined in a specific manner successfully explain the variation of the line width with concentration strongly associated with binary systems. A readily usable empirical relationship for line width is suggested. It has been demonstrated that it can successfully explain the line width variation with concentration in a given class of hydrogen-bonded systems taking some representative binary mixtures.     

Equation of state for hard-spheres and excess function calculations of binary liquid mixtures

Using our previously proposed matrix method, an equation of state for hard spheres is presented, which can reproduce the exact values of the first-eight virial coefficients. This equation meets both the low density and the close-packed limits and can predicts the first order fluid–solid phase transition of hard spheres. The results obtained show that the new equation of state can correlate the simulation data of compressibility factor up to high densities better than other equations of state.The new equation of state is extended to mixtures of hard spheres and excess functions of various binary liquid mixtures are calculated using the perturbation theory of Leonard–Henderson–Barker. The results are compared with existing theoretical and experimental data and with those calculated by other hard-sphere equations of state.It is seen that the results obtained by the new equation of state is quite satisfactory compared to other equations of state for the hard spheres and mixture of hard spheres.     

Thermodynamics of binary mixtures: excess volumes of mixing of some binary 1,2-dichloroethane mixtures

The excess volumes, V^E, of some binary 1,2-dichloroethane mixtures have been determined at 30°C. The data have been examined for Cell model theory of Prigogine and Flory's theory. Both theories have been found to fail to fit the results with useful accuracy.     

Fundamental measure density functional theory studies on the freezing of binary hard-sphere and Lennard-Jones mixtures

Free energies and correlation functions of liquid and solid hard-sphere (HS) mixtures are calculated using the fundamental measure density functional theory. Using the thermodynamic perturbation theory the free energies of solid and liquid Lennard-Jones (LJ) mixtures are obtained from correlation functions of HS systems within a single theoretical approach. The resulting azeotrope- and spindle-type solid-liquid phase diagrams of HS and LJ binary mixtures are in good agreement with the corresponding ones from computer simulations.     

On the density and viscosity of (water + dimethylsulphoxide) binary mixtures

Density and viscosity of (water + dimethylsulphoxide) were measured precisely over the whole composition range at T = (298.15, 303.15, 308.15, 313.15, and 318.15) K. Differences between values from different authors are clarified and more reliable partial molar volumes are obtained.     

Self-assembly of cetylpyridinium chloride in water-DMF binary mixtures: a spectroscopic and physicochemical approach

The aggregation behavior of cetylpyridinium chloride (CPyCl) in N,N-dimethylformamide (DMF)-water mixed solvents was investigated using electrical conductivity and spectroscopic techniques. Micellar and thermodynamic parameters (DeltaG(m)(0), DeltaH(m)(0), DeltaS(m)(0) and Delta(m)C(p)(0)) were obtained from the temperature dependence of critical micelle concentrations in various aqueous mixtures of DMF. The differences in the Gibbs energies of micellization of CPyCl between water and binary solvents were determined to evaluate the influence of the cosolvent. The effect of cosolvent on the Krafft temperature (K(T)) and on the aggregation number was also analyzed. Micellar micropolarity was examined spectrophotometrically using two different probes, methyl orange (MO) and methylene blue (MB), and was found to increase with DMF addition, accompanied by an enhanced solvation. The mechanism of docking of surfactant and the probe molecules in the system were obtained by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.     

Synergisms in binary surfactant mixtures

Significant correlations become apparent between synergisms of micelle formation in surfactant mixtures and a series of physico-chemical properties and applications. Examples are emulsifying, dispersing, wetting, flotation, washing and cleaning ability. As a result, the effect of a co-surfactant with respect to problems of application can be predicted by a few surface tension measurements only.     

Metal-organic approach to binary optical memory

Two new Ru(II) diimine chromophores, each containing a single photochromic dianthryl unit, have been prepared and characterized. The photoluminescence from the Ru(II) complexes is modulated by the photochromic action of the dianthryl species, which serves as a triplet energy transfer quencher in one photochromic state. The coupling of the dianthryl photochromic action to the Ru(II) complex emission permits nondestructive photoluminescence readout of binary information photochemically recorded on the molecular level. Luminescent images stored on polystyrene films that contain these molecules maintained their integrity for periods of months with no apparent degradation or variation in the image resolution, suggesting their durability for long-term storage in read-only memory applications.     

Magnetic susceptibilities of binary non-electrolyte mixtures

Molar magnetic susceptibilities are determined by theGouy method for the following four systems: dichloromethane + methyl acetate,n-pentane + dichloromethane,n-pentane + methyl acetate and 2-propanol +n-pentane, in whichn-pentane is a non-polar molecule and the other three are polar while 2-propanol is associated in its pure state. Excess diamagnetic susceptibilities are calculated to obtain information about possible interactions. Diamagnetic susceptibilities were related with molecular polarizabilities byBoyer-Donzelot's equation and compared with experimental results.

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Magnetische Suszeptibilitäten binärer Nicht-Elektrolyt-Mischungen

Zusammenfassung Für folgende vier Systeme wurden die molaren magnetischen Suszeptibilitäten mittels derGouy-Methode bestimmt: Dichlormethan + Methylacetat,n-Pentan + Dichlormethan,n-Pentan + Methylacetat, und 2-Propanol +n-Penten; dabei istn-Pentan ein nicht-polares Molekül, die anderen sind polar, wobei 2-Propanol zusätzlich Assoziation zeigt. Es werden Exzess-diamagnetische Suszeptibilitäten berechnet, um Informationen bezüglich möglicher Wechselwirkungen zu erhalten. Die diamagnetischen Suszeptibilitäten wurden mit den molekularen Polarisierbarkeiten über dieBoyer-Donzelot-Beziehung in Relation gesetzt und mit den experimentellen Resultaten verglichen.