Non-Lorentz–Berthelot Lennard-Jones mixtures: A systematic study

Binary mixtures of two identical Lennard-Jones fluids with non-Lorentz–Berthelot combining rules have been simulated over the entire concentration range at three state points in order to examine the effect of cross interactions on the mixing properties, excess volumes and enthalpies, and partial molar volumes, and on the structure. Various combinations of deviations, in both the energy and size cross parameters, from the Lorentz–Berthelot rule, have been considered and the results analyzed using a recently proposed method based on the Tikhonov regularization. It is found that the most important is the size cross parameter and that by varying the combining rules a variety of qualitatively different behavior can be produced including, e.g., a minimum in the partial molar volumes observed otherwise only in complex mixtures of associating fluids; occurrence of this minimum seems to be associated with changes in the second coordination shell as witnessed by the pair correlation function.     

Isentropic expansion and related thermodynamic properties of non-ionic amphiphile-water mixtures

A concise thermodynamic formalism is developed for the molar isentropic thermal expansion, ES,m = ( partial differential Vm/ partial differential T)(Sm,x), and the ideal and excess quantities for the molar, apparent molar and partial molar isentropic expansions of binary liquid mixtures. Ultrasound speeds were determined by means of the pulse-echo-overlap method in aqueous mixtures of 2-methylpropan-2-ol at 298.15 K over the entire composition range. These data complement selected extensive literature data on density, isobaric heat capacity and ultrasound speed for 9 amphiphile (methanol, ethanol, propan-1-ol, propan-2-ol, 2-methylpropan-2-ol, ethane-1,2-diol, 2-methoxyethanol, 2-ethoxyethanol or 2-butoxyethanol)-water binary systems, which form the basis of tables listing molar and excess molar isobaric expansions and heat capacities, and molar and excess molar isentropic compressions and expansions at 298.15 K and at 65 fixed mole fractions spanning the entire composition range and fine-grained in the water-rich region. The dependence on composition of these 9 systems is graphically depicted for the excess molar isobaric and isentropic expansions and for the excess partial molar isobaric and isentropic expansions of the amphiphile. The analysis shows that isentropic thermal expansion properties give a much stronger response to amphiphile-water molecular interactions than do their isobaric counterparts. Depending on the pair property-system, the maximum excess molar isentropic value is generally twenty- to a hundred-fold greater than the corresponding maximum isobaric value, and occurs at a lower mole fraction of the amphiphile. Values at infinite dilution of the 9 amphiphiles in water are given for the excess partial molar isobaric heat capacity, isentropic compression, isobaric expansion and isentropic expansion. These values are interpreted in terms of the changes occurring when amphiphile molecules cluster into an oligomeric form. Present results are discussed from theoretical and experimental thermodynamic viewpoints. It is concluded that isentropic thermal expansion properties constitute a new distinct resource for revealing particular features and trends in complex mixing processes, and that analyses using these new properties compare favourably with conventional approaches.     

Physicochemical Properties, <Superscript>1</Superscript>H-NMR,Ab Initio Calculations and Molecular Interaction in Binary Mixtures of <Emphasis Type="Italic">N</Emphasis>-methylimidazole with Methanol

Over the full molar fraction range, the density, viscosity, refractive index, conductivity and pH at the temperatures (298.15, 308.15, and 318.15) K, mixing enthalpy at T?=?298.15 K, and ¹H-NMR were measured for the binary mixtures of x N-methylimidazole (hereafter abbreviated to N-mim)?+?(1???x) methanol, together with ab initio calculations. The thermodynamic parameters of activation for viscous flow were calculated and analyzed. The excess molar volume, viscosity deviation, deviation for the logarithm of viscosity, refractive index deviation and the excess refractive index, excess Gibbs energy of activation of viscous flow and the molar mixing enthalpy were calculated and fitted with a Redlich–Kister equation. The partial molar mixing enthalpies and the protons’ chemical shift changes of N-mim and methanol were calculated and explained. An increase in temperature leads to the excess molar volume becoming more negative, whereas the deviations for the logarithm of viscosity, viscosity deviation and the excess Gibbs energy of activation of viscous flow become less positive; in contrast the refractive index deviation and the excess refractive index become less positive at first and then become more positive. The activation of the viscous fluid is a more ordered process. The physicochemical properties, ab initio calculations, combined with the ¹H-NMR results reveal that the molecular interactions among unlike molecules is stronger than that between like ones. There is an ionization process and hydrogen bond interaction between N-mim and methanol, the predominant interaction is N-mim:methanol?=?1:1 hydrogen-bonded network, where the methyl groups of methanol and N-mim, respectively, are electron-withdrawing and electron-donating groups.     

Thermodynamic Properties of Alkanediols+Acetates at 298.15 K

In this work we present experimental values of the density, refractive index, speed of sound, isentropic compressibility and liquid-liquid equilibria of the binary mixtures (methyl acetate, ethyl acetate, propyl acetate, and butyl acetate) with (1,2-ethanediol, 1,2-propanediol, or 1,3-propanediol) at 298.15 K and atmospheric pressure, as a function of mole fraction. From the experimental values, the corresponding excess and deviation values were computed (excess molar volumes, changes of refractive index on mixing, and changes of isentropic compressibility), variable-degree polynomials being fitted to the results. The validity of different estimation methods for predicting the experimental values of physical properties was tested. The limiting partial excess molar volume of the components in each binary mixture was determined by means of predetermined Redlich-Kister parameters. Group contribution method (UNIFAC-Dortmund) was applied in order to compare their capability in predicting the experimental equilibria values. This revised version was published online in July 2006 with corrections to the Cover Date.     

Volumetric Properties of Difurylmethane in Methanol from 288.15 to 308.15 K

The densities of binary systems of difurylmethane (DFM) in methanol have been measured with an Anton Parr DMA 4500 vibrating-tube densimeter over the entire composition range at intervals of 5 K in the temperature range between 288.15 and 308.15 K. Excess molar volumes of the mixture, apparent molar volumes of DFM, and excess partial molar volumes of both components have been calculated to provide insight into the intermolecular interaction present in the mixtures investigated. Excess molar volumes have been fitted to a Redlich–Kister equation and they exhibited negative deviations from ideal behavior. Both the apparent molar volume of DFM and excess partial molar volumes of DFM and methanol exhibit a dependence on composition but are less sensitive to temperature.     

Refractive Index of Liquid Mixtures: Theory and Experiment

An innovative approach is presented to interpret the refractive index of binary liquid mixtures. The concept of refractive index “before mixing” is introduced and shown to be given by the volume‐fraction mixing rule of the pure‐component refractive indices (Arago–Biot formula). The refractive index of thermodynamically ideal liquid mixtures is demonstrated to be given by the volume‐fraction mixing rule of the pure‐component squared refractive indices (Newton formula). This theoretical formulation entails a positive change of refractive index upon ideal mixing, which is interpreted in terms of dissimilar London dispersion forces centred in the dissimilar molecules making up the mixture. For real liquid mixtures, the refractive index of mixing and the excess refractive index are introduced in a thermodynamic manner. Examples of mixtures are cited for which excess refractive indices and excess molar volumes show all of the four possible sign combinations, a fact that jeopardises the finding of a general equation linking these two excess properties. Refractive indices of 69 mixtures of water with the amphiphile (R,S)‐1‐propoxypropan‐2‐ol are reported at five temperatures in the range 283–303 K. The ideal and real refractive properties of this binary system are discussed. Pear‐shaped plots of excess refractive indices against excess molar volumes show that extreme positive values of excess refractive index occur at a substantially lower mole fraction of the amphiphile than extreme negative values of excess molar volume. Analysis of these plots provides insights into the mixing schemes that occur in different composition segments. A nearly linear variation is found when Balankina’s ratios between excess and ideal values of refractive indices are plotted against ratios between excess and ideal values of molar volumes. It is concluded that, when coupled with volumetric properties, the new thermodynamic functions defined for the analysis of refractive indices of liquid mixtures give important complementary information on the mixing process over the whole composition range.     

Excess enthalpies of alcohol + amine mixtures. Experimental results and theoretical description using the ERAS-model

New experimental data of the molar excess enthalpy H^E of mixtures containing eight liquids - propylamine + methanol, ethanol, propan-1-ol, butan-1-ol, butylamine + methanol, ethanol, propan-1-ol, butan-1-ol - are presented using a quasi-isothermal flow calorimeter. The results are used for testing the ERAS-model which provides a theoretical concept accounting for the self-association and cross-association of alcohol and amine molecules, as well as for non-associative intermolecular interactions. Excess molar volumes V^E are also successfully described by the model. It turns out that the strong cross-association occurring between alcohol and amine molecules is the predominant reason for the remarkably low exothermic values of H^E observed for the mixtures studied.     

Molecular Interactions in Binary Mixtures of Benzene with 1-Alkanols(C5,C7,C8) at 35℃:An Ultrasonic Study

Densities and ultrasonic speeds have been measured in binary mixtures of benzene with 1‐pentanol, 1‐heptanol and 1‐octanol, and in the pure components, as a function of composition at 35 °C. The isentropic compressibility, intermolecular free length, relative association, acoustic impedance, isothermal compressibility, thermal expansion coefficient, deviations in isentropic compressibility, excess free length, excess volume, deviations in ultrasonic speed, excess acoustic impedance, apparent molar compressibility, apparent molar volume, partial molar volume of 1‐alkanol in benzene have been calculated from the experimental data of densities and ultrasonic speeds. The variation of these parameters with composition indicates weak interaction between the component molecules and this interaction decreases in the order: 1‐pentanol > l‐heptanol> 1‐octanol. Further, theoretical values of ultrasonic speeds were evaluated using free length theory, collision factor theory, Nomoto's relation and Van Dæl‐Vangeel ideal mixing relation. The relative merits of these theories and relations were discussed for these systems.     

Excess and apparent molar volumes of mixtures of water and acetonitrile between 0 and 25°C

From densities measured at 0, 1, 2.5, 5, 10 and 25°C of mixtures of water and acetonitrile, the excess molar volumes and the apparent and partial molar volumes of both components have been derived as a function of mixture composition. Contrary to results on enthalpies of solution in mixtures of water and acetonitrile, the values obtained do not show substantial changes around 0.7 mole fraction of water. At this composition and at low temperatures, the excess molar volumes exhibit a rather flat minimum and the apparent and partial molar volumes of water show an inflection.     

Derived Properties of Binary Mixtures Containing (Acetone or Methanol) + Hydroxil Compounds

Abstract

This work reports values of the density, refractive index and speed of sound of the binary mixtures acetone or methanol with (2-methyl, 1-propanol, 3-methyl, 1-butanol, 1,2-ethanediol, 1,2-propanediol and 1,3-propanediol) at 298.15 K and atmosphere, as a function of the mole fraction. From the experimental values, the corresponding excess and derived magnitudes were computed (excess molar volumes, changes of refractive index on mixing and changes of isentropic compressibility on mixing), variable-degree polynomials being fitted to the results. Only expansive trend was observed for those mixtures enclosing branched alcohols. The influence of the hydroxil group in the nonideal behaviour of these mixtures were analyzed in terms of the partial molar excess volumes.     

Volumetric properties of aqueous electrolytes at high temperature. II. B(OH)3 and B(OH)3−NaB(OH)4−NaOH mixtures up to 523 K

The densities of boric acid aqueous solutions and sodium hydroxide-sodium borate mixtures were measured as a function of concentration, between 375 and 523 K at pressures close to saturation. The partial molar volumes of boric acid were obtained and it was found that they are almost independent of the concentration. The partial molar volumes of the sodium hydroxide-sodium borate mixtures were fitted to the Pitzer equation for mixtures using the known parameters for NaOH. Thus, the partial molar volume at infinite dilution and the Pitzer parameters of sodium borate could be obtained by assuming ideal mixing.     

Excess enthalpies of binary solvent mixtures of N-methylacetamide with aliphatic alcohols

The molar excess enthalpies H _m ^E of binary solvent mixtures of N-methylacetamide with methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol have been measured with a flow microcalorimeter at 40°C. The excess enthalpies are negative for methanol and positive for the other alcohols over the whole composition range, except for t-butanol which exhibits a sigmoid curve with a deep minimum at low mole fractions of the amide. The values for the primary alcohols increase in the order methanol < ethanol < 1-propanol < 1-butanol. The partial molar excess enthalpies have also been evaluated. Intermolecular interactions in these mixtures are discussed through comparison of the results with those for the corresponding binary mixtures of N,N-dimethylacetamide.     

Limiting Partial Molar Excess Heat Capacities and Volumes of Selected Organic Compounds in Water at 25°C

Well-known Picker flow microcalorimeters for the differential measurements of volumetric heat capacities have been employed in conjunction with vibrating tube densimeters to determine the molar heat capacity, volume, and the apparent properties in dilute aqueous solutions for 17 organic solutes of moderate hydrophobicity. The dependence on concentration of the apparent properties allowed the limiting partial molar quantities at infinite dilution to be extrapolated and the limiting partial molar excess quantities to be evaluated. Comparison with available literature data shows good agreement. The application of group contribution rules to the limiting partial properties has been tested using the original method and parameters proposed by Cabani et al. The predicted values of the partial molar volumes are in fair agreement with the present data except for some less common solutes. With partial molar heat capacities, the agreement is less satisfactory. To improve the performance of the method, missing parameters for some types of monofunctional and bifunctional molecules have been evaluated.     

Thermodynamics of aqueous mixtures of nonelectrolytes. IV. Excess volumes of water-acetonitrile mixtures from 15 to 35°C

Excess volumes of water-acetonitrile mixtures were obtained from measurements of density over the entire mole fraction range and at 5 degree intervals from 15 to 35°C. Partial molar excess volumes at the five temperatures, excess coefficients of thermal expansion at 25°C and partial molar excess expansibilities at 25°C were derived from the results. The values of the various volumetric properties are compared with data from the literature.Issued as NRCC No. 19500     

Excess Molar Enthalpies and Excess Molar Volumes of (Water+Octan-1-ol or +Octan-2-ol) at 298.15 K

The excess molar enthalpies and volumes have been determined for the binary system (water+octan-1-ol or +octan-2-ol) by means of direct calorimetric and densimetric measurements in the miscibility range. The experimental data were described through a Redlich-Kister type equation. For excess enthalpies a sigmoidal shape is predicted,while excess volumes are negative except for a little positive queue observed for(water+octan-1-ol) system at very low water content. Also the partial molar enthalpies of solution and the partial molar volumes of water in the two isomeric octanols at infinite dilution have been evaluated and discussed. A comparison is made between excess enthalpies and excess free energies calculated by the UNIFAC method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Volumetric properties of aqueous electrolytes at high temperature. III. B(OH)3−NaBx(OH)3x+1−NaOH mixtures up to 523 K

The densities of aqueous solutions resulting from the partial neutralization of boric acid with sodium hydroxide were measured as a function of concentration, between 375 K and 523 K at pressures close to saturation. The speciation in this system is complex, di- and triborate ions are present in addition to the monoborate ion. The concentration dependence of the apparent partial molar volume of the mixture can be described using the Pitzer equation only if the formation of the polyborate species in the concentrated solutions is taken into account. The partial molar volumes at infinite dilution for the diborate and triborate anions, obtained by assuming ideal mixing, are reported in the range of temperature studied.     

Thermodynamics of aqueous mixtures of nonelectrolytes. I. Excess volumes of water-n-alcohol mixtures at several temperatures

Excess volumes of binary mixtures of water with methanol, ethanol and 1-propanol were obtained from density measurements at 5 degree intervals from 15 to 35°C over the entire composition range. Excess thermal expansion coefficients, partial molar excess volumes, and expansibilities at 25°C were derived from the results. The significance of these values is discussed in relation to hypothesized structural changes in the mixtures.     

四苯硼钠水溶液的系列热力学性质

在288.15～318.15K范围内,用等压法测定了四苯硼钠在不同浓度水溶液中的平均活度系数和渗透系数,计算了不同浓度时的超额自由能、相对偏摩尔焓、偏摩尔热容。经计算机曲线拟合给出热力学性质的经验计算公式。     

Volumetric properties of (1-propoxypropan-2-ol + water) mixtures between (283 and 303) K: The effect of branching on alkoxyalcohols

Accurate density values are reported for aqueous binary mixtures of 1-propoxypropan-2-ol (1-PP-2-ol) over the whole composition range and temperatures between (283 and 303) K at intervals of 5 K. Excess molar volumes of the mixture, , apparent molar volumes of 1-PP-2-ol, V_φ,2, as well as excess partial molar volumes, , of both components were obtained over the entire composition and temperature ranges. Thermal expansibility effects on this (amphiphile + water) mixture are analysed in terms of excess molar isobaric expansions, , of the mixture and from the temperature dependence of limiting excess partial molar isobaric expansions, , for both chemical substances in the mixture. An analytical method based on Redlich−Kister fitting equations for as a function of the mole fraction has been used to obtain limiting excess partial molar volumes, . The excess properties are referred to a thermodynamically defined ideal liquid mixture. Interesting insights into the mixing process are gained from the visual impact of plots showing the composition and temperature dependence of different excess molar thermodynamic properties. The choice of 1-PP-2-ol was specially meant to highlight the role of branching in the alcohol versus alkoxy moieties. The present thermodynamic data are compared with that for isomeric 2-butoxyethanols, which are structural isomers of 1-PP-2-ol, and for 2-isopropoxyethanol. From this comparison an extended insight is gained into the role of branching and chain length on the mixing process and particularly in changes of local H-bond patterns of hydration water.