Characterization and preferential solvation of the hexane/hexan-1-ol/methylbenzoate ternary solvent

The thermophysical properties of the hexane/hexan-1-ol/methylbenzoate ternary system and its binary constituents were studied at 298.15 K over the whole composition range. The excess and mixing properties calculated from the experimental values combined with the mixture activity coefficients deduced from the UNIFAC group contribution method were used to calculate the integrals of the Kirkwood-Buff fluctuation theory for the ternary system and the binary constituents. Also the local composition and the excess or deficit number of molecules around a central molecule have been determined. The volumetric properties for the ternary system and its binary constituents were correlated and predicted successfully with several cubic equations of state combined with two simple mixing rules. The structural and intermolecular interactions of the mixtures were analyzed on the basis of the measured and derived properties.     

Excess Thermodynamic Properties of Binary Liquid Mixtures Containing N,N -Dimethylacetamide with Some Alkan-1-Ols (C 1 -C 6 ) At 298.15 K

Excess molar enthalpies, $ H_m^E $ of N , N -dimethylacetamide + methanol, + ethanol, + propan-1-ol, + butan-1-ol, + pentan-1-ol, and + hexane-1-ol have been determined at 298.15 K and atmospheric pressure using a Parr 1455 solution calorimeter. While the excess molar enthalpies are negative for methanol and ethanol mixtures, those for propan-1-ol, butan-1-o1, pentane-1-ol, and hexan-1-ol mixtures are positive over the entire range of composition of N , N -dimethylacetamide. The $ H_m^E $ at around x , 0.5 follow the order: methanol<ethanol<propan-1-ol<butan-1-ol<pentan-1-ol<hexan-1-ol. The results are explained in terms of the self-association exhibited by the alkan-1-ols and the formation of aggregates between unlike molecules through OHO hydrogen bonding. The experimental results for mixtures are well represented by the Redlich - Kister equation.     

The Kinematic Viscosity of Binary Liquid Mixtures of n-Nonane with Propan-1-ol,Butan-1-ol,and Pentan-1-ol over the Temperature Range 193.15–313.15 K

The kinematic viscosity of n-nonane mixtures with propan-1-ol, butan-1-ol, and pentan-1-ol was measured over the temperature range 293.15–313.15 K. For all systems, negative deviations of viscosity from additive values were obtained; the deviations increased in magnitude as the temperature and alkan-1-ol hydrocarbon radical length increased. The activation energy of viscous flow was calculated in terms of the Eyring theory and free volume theory in the usual and extended (with the inclusion of molecular association) variants at equimolar mixture compositions. The behavior of the concentration dependences of viscosity and the activation energy of viscous flow in alkan-1-ol-n-alkane mixtures was found to be controlled by molecular association processes.     

Thermodynamic Properties of Binary Liquid Mixtures of n-Dodecane with an Alkan-1-ol or an Alkan-2-ol at 298.15 K: A Comparative Study

Experimental densities (ρ), viscosities (η), and speeds of sound (u) of the binary mixtures of n-dodecane with an alkan-1-ol (hexan-1-ol, heptan-1-ol, octan-1-ol) or an alkan-2-ol (hexan-2-ol, heptan-2-ol and octan-2-ol) were measured over the whole mixture composition range at T = 298.15 K. From these data, the excess molar volume ( $ V_{\text{m}}^{\text{E}} $ V m E ), deviations in viscosity (Δη), and excess isentropic compressibility ( $ \kappa_{S}^{\text{E}} $ κ S E ) have been calculated. The results were fitted by means of the Redlich–Kister equation, in order to estimate the binary coefficients and standard errors. Differences among these binary systems are ascribed to the different association abilities of the alkan-1-ols and alkan-2-ols. Experimental data on the constituted binaries were analyzed using McAllister’s multi-body interaction model, the Jouyban–Acree model, the Prigogine–Flory–Patterson theory, and the Bloomfield and Dewan model. The experimental and calculated quantities are used to study the nature of mixing behavior among the mixtures.     

The excess molar enthalpies and volumes of (N-methyl-2-pyrrolidinone + an alkan-1-ol) at T=298.15 K

The excess molar enthalpies H_m^E, for the mixtures (N-methyl-2-pyrrolidinone + ethanol, or pentan-1-ol, or hexan-1-ol, or heptan-1-ol, or octan-1-ol, or nonal-1-ol, or decan-1-ol, or undecan-1-ol) at T=298.15 K and atmospheric pressure have been obtained using flow calorimetry. Excess molar volumes at T=298.15 K and atmospheric pressure have also been determined for (N-methyl-2-pyrrolidinone + nonal-1-ol, or decan-1-ol, or undecan-1-ol) from density measurements using a vibrating tube densimeter. The experimental results have been correlated and compared with the results from the Flory–Benson–Treszczanowicz (FBT) theory and from the Extended Real Associated Solution (ERAS) model. The ERAS model accounts free volume effects according to the Flory–Patterson model and additionally association effects between the molecules involved. For the mixtures studied here the association effects arise from the self association of an alkan-1-ol molecules and also the cross-association of the proton of the alkan-1-ol with carbonyl oxygen of N-methyl-2-pyrrolidinone (NMP) molecule. The parameters adjusted to the mixtures properties are two cross-association parameters and the interaction parameter responsible for the exchange energy of the van der Waals interactions. Self-association parameters of the alcohols and NMP are taken from the literature.     

A fluctuation theory analysis of the salting-out effect

An analysis of the salting-out, or Sechenow, effect is given in terms of Kirkwood-Buff, or fluctuation, integrals. The analysis is formally exact but cannot easily be applied in its original form. When the solute that is being salted out is sparingly soluble, simplifications arise and the theory can be used to compute one of the Kirkwood-Buff integrals which is otherwise difficult to obtain.     

Aqueous tert-butanol mixtures: a model for molecular-emulsions

By analogy with micro-emulsion, we introduce the molecular-emulsion picture to describe particular aqueous mixtures. The analogy is set by introducing the equivalent of the Teubner-Strey structure factor, the latter which is traditionally used to describe the structure of micro-emulsions. The main difference resides in the fact that the size of the oil and water domains are not in the micrometer, but in the nanometer scale. This implies that the molecular size and the molecular geometry cannot be neglected anymore. The introduction of this analogy is used to settle the problem of properly describing with computer simulations highly micro-heterogeneous aqueous mixtures. In particular, the issue of whether or not the Kirkwood-Buff integrals represent solely concentration fluctuations is settled by showing the contribution of the micro-heterogeneity to these integrals through the presence of an associated pre-peak in the structure factors. Both the Optimized Potentials for Liquid State (OPLS) and Transferable Potential for Phase Equilibria-United Atoms (TraPPE-UA) force fields for tert-butanol turn out to be remarkably good in describing the structure of the corresponding aqueous mixtures, when the above-mentioned analogy with micro-emulsion is introduced to correct for the computational artifacts in the Kirkwood-Buff integrals.     

Local composition in solvent + polymer or biopolymer systems

The focus of this paper is on the application of the Kirkwood-Buff (KB) fluctuation theory to the analysis of the local composition in systems composed of a low molecular weight solvent and a high molecular weight polymer or protein. A key quantity in the calculation of the local composition is the excess (or deficit) of any species i around a central molecule j in a binary mixture. A new expression derived by the authors (J. Phys. Chem. B 2006, 110, 12707) for the excess (deficit) is used in the present paper. First, the literature regarding the local composition in such systems is reviewed. It is shown that the frequently used Zimm cluster integral provides incorrect results because it is based on an incorrect expression for the excess (or deficit). In the present paper, our new expression is applied to solvent + macromolecule systems to predict the local composition around both a solvent and a macromolecule central molecule. Five systems (toluene + polystyrene, water + collagen, water + serum albumin, water + hydroxypropyl cellulose, and water + Pluronic P105) were selected for this purpose. The results revealed that for water + collagen and water + serum albumin mixtures, the solvent was in deficit around a central solvent molecule and that for the other three mixtures, the opposite was true. In contrast, the solvent was always in excess around the macromolecule for all mixtures investigated. In the dilute range of the solvent, the excesses are due mainly to the different solvent and macromolecule sizes. However, in the dilute range of the macromolecule, the intermolecular interactions between solvent and macromolecule are mainly responsible for the excess. The obtained results shed some light on protein hydration.     

Thermodynamic properties of strong electrolyte solutions from correlation functions

General relations are presented to relate the fluctuation thermodynamic properties of multicomponent electrolyte solutions (concentration derivatives of the chemical potential, partial molar volume, and compressibility) to integrals of the total correlation function (Kirkwood-Buff solution theory) and of the nondivergent portion of the direct correlation function. Detailed expressions are given for the single-salt, single-solvent system. It appears that the direct correlation function expressions may be of more practical use in developing correlations for solution properties because, unlike the total correlation functions, terms exist which distinguish between cation and anion interactions with water and with other ions.     

Experimental (solid + liquid) phase equilibria of (alkan-1-ol + benzonitrile), (amine + benzonitrile) binary mixtures,and (decan-1-ol + decylamine + benzonitrile) ternary mixtures

(Solid + liquid) phase diagrams, SLE have been determined for (octan-1-ol, or nonan-1-ol, or decan-1-ol, or undecan-1-ol + benzonitrile) and for (hexylamine, or octylamine, or decylamine, or 1,3-diaminopropane + benzonitrile) using a cryometric dynamic method at atmospheric pressure. Simple eutectic systems with complete immiscibility in the solid phase and complete miscibility on the liquid phase have been observed. The solubility decreases with an increase of the number of carbon atoms in the alkan-1-ol, or amine chain. The temperature of the eutectic points increases and shifts to lower alkan-1-ol, or amine mole fractions as the alkyl chain length of the alkan-1-ol, or amine increases. The higher intermolecular interaction was observed for the (alkan-1-ol + benzonitrile) systems.     

Kirkwood-Buff integrals and density fluctuations in aqueous solution of caffeine

The Kirkwood-Buff theory is applied to caffeine aqueous solution. The integrals of radial distribution functions are calculated from the osmotic coefficient, density and sound velocity data at 25°C. The results are discussed in terms of density fluctuations of two components and the correlation between them. It is found that the concentration dependence of Kirkwood-Buff integrals reflects the association tendency of caffeine and its strong influence on the properties of the solvent.     

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.     

Thermodynamics of Mixtures Containing Organic Carbonates. Part XV. Application of the Kirkwood-Buff Theory to the Study of Interactions in Liquid Mixtures Containing Dialkyl Carbonates and Alkanes,Benzene, CCl4 or 1-Alkanols

Binary liquid mixtures containing a dialkyl carbonate (dimethyl or diethyl carbonate) and organic solvents such as alkanes, benzene, CCl₄, or 1-alkanols were studied within the framework of the Kirkwood-Buff formalism. The Kirkwood-Buff integrals, linear coefficients of preferential solvation and local mole fractions were calculated. Results were interpreted assuming that the mixtures with alkanes or 1-alkanols are not random mixtures, which can be ascribed to the existence of strong dipolar interactions between like molecules. Systems containing benzene or CCl₄ are both random and more ordered because of the charge transfer or dipole/induced dipole interactions between the polar group of the solute (O–CO–O) and the polarizable solvent molecules. The effect of increasing temperature was also examined.     

Solution thermodynamics and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K was reported. Mole fraction solubility varies continuously from 2.85 × 10^–9 in neat water to 2.39 × 10^–3 in neat 1,4-dioxane. Solubility behaviour was adequately correlated by means of the Jouyban-Acree model. Based on the inverse Kirkwood-Buff integrals, preferential solvation parameters were calculated. Triclocarban is preferentially solvated by water in water-rich mixtures (0.00 < x₁ < 0.18) and also in 1,4-dioxane-rich mixtures (0.78 < x₁ < 1.00) but preferentially solvated by 1,4-dioxane in mixtures with similar solvent compositions.     

Analysis of the pressure effect on the local composition in a water-alkanol mixture using Kirkwood-Buff integrals

Kirkwood-Buff integrals are calculated from the thermodynamic data for binary mixtures of water with methanol, ethanol, 1-propanol, and 2-propanol at a temperature of 298.15 K in the pressure range from atmospheric to 100 MPa. The values of local compositions Δn _ij are calculated which characterize the excess (or deficit) of molecules i around the central molecule j. It is found that the pressure affects destructively the homoassociation in all mixtures studied. In a series MeOH < EtOH < 2-PrOH < 1-PrOH an excess of molecules around the similar type molecules increases in the local environment and the pressure effect on the local composition is enhanced.     

Excess molar enthalpies of formamide + some alkan-1-ols (C1-C6) and their correlations at 298.15 K

Excess molar enthalpies, H^E for the binary systems formamide+methanol, + ethanol, + propan-1-ol, + butan-1-ol, + pentan-1-ol, and + hexan-1-ol have been measured at 298.15 K and atmospheric pressure with a Paar 1455 solution calorimeter. All the system present endothermic events and showed maximum positive H^E values around 0.40-0.50 mole fraction of formamide. The H^E values increases in the order: methanol<ethanol<propan-1-ol<butan-1-ol<pentan-1-ol<hexan-1-ol. Experimental showed insolubility of hexan-1-ol in formamide around x≅0.5 mole fraction of formamide. The excess enthalpies of the above mentioned binary systems, were used to discuss interaction between the alkan-1-ols and formamide molecules. The results are interpreted to gain insight into the changes in molecular association equilibria and structural effects in these systems through O···HO hydrogen bonding. The experimental data have been correlated using Redlich-Kister polynomials. In this research work, the thermodynamics models were also tested: NRTL, Wilson models and their parameters were calculated. The correlation of excess enthalpy data in the systems using NRTL model provides good results.     

Structure of aqueous solutions of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate by small-angle neutron scattering

The structure of aqueous solutions of a prototype ionic liquid, the short alkyl chain 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) has been investigated by small-angle neutron scattering. Concentration fluctuations and Kirkwood-Buff integrals have been calculated, and the results are in good agreement with corresponding data calculated herein from vapor pressure measurements. The large concentration fluctuations and Kirkwood-Buff integral values indicate that the system is in the vicinity of phase separation, which is known to occur some 20 K below room temperature, at a salt mole fraction of around 0.075.     

The Kirkwood-Buff integrals for one-component liquids

The Kirkwood-Buff integrals (KBIs) for one-component systems are calculated from either the pair correlation functions or from experimental macroscopic quantities. As in the case of mixtures, the KBIs provide important information on the local densities around a molecule. In the low density limit (rho-->0) one can extract from the KBI some information on the strength of the intermolecular forces. No such information may be extracted from the KBIs at higher densities. We used experimental data on densities and isothermal compressibilities to calculate the KBIs for various liquids ranging from inert molecules, to hydrocarbons, alcohols, and liquid water.