A method to determine the Gibbs energy of specific interactions in solutions. Hydrogen bonding of proton donating solutes in basic solvents

One of two fundamental types of solute–solvent intermolecular interactions are the specific interactions, such as hydrogen bonding complexation between solute and solvent. The Gibbs energy of specific interactions is an important quantity that determines rate and equilibrium constants in solutions, but it is difficult to obtain by direct measurement. We proposed equations allowing to determine the contribution of specific interactions to the Gibbs energy of solvation in nonelectrolyte solutions. Applying it for the case of proton donating solutes with one acidic hydrogen atom dissolved in basic solvents, we obtained the values of the Gibbs energies of 1:1 complexation in pure base. These values have been compared with the Gibbs energies of 1:1 complexation in tetrachloromethane. Most of the hydrogen bonds are found to have the same energy in pure base and in CCl₄, however, some weakly bound complexes seem to become even more weakened in pure base medium. Suggested method is applicable in a general situation when multiple associates of different stoichiometry and structure are formed.     

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.     

Excess volumes,isentropic compressions,and isobaric heat capacities for methanol mixed with other alkanols at 25°C

Excess volumes, excess isentropic compressions and excess isobaric heat capacities for binary liquid mixtures of methanol with ethanol, 1-propanol and 1-butanol have been determined at 25° C. These thermodynamic functions are smaller than those for alkanol + water mixtures and are correlated with the difference in the alkyl chain length in two of the alkanol molecules. The behavior of the component molecules in solution is found to be similar to that in the pure liquid. The excess isentropic compressions of methanol + 1-butanol show an S-shaped concentration dependence with a positive lobe in the methanol rich range and a negative lobe in the methanol poor range, which resembles that of the excess Gibbs energy reported by Polak et al.     

A method for calculating the Gibbs energy of nonspecific solvation

A method for calculating the Gibbs energy of nonspecific solvation of nonelectrolytes was suggested. The new equation for the Gibbs energy of nonspecific solvation contains one solvent parameter that characterize nonspecific solvent-solute interactions and two experimental Gibbs energies of solvation in two standard solvents. The method is applicable to a wide range of solutes and solvents. It was successfully used to describe some 800 Gibbs energies of solvation for systems without specific solvent-solute interactions.     

含酯基Gemini表面活性剂在有机醇-水体系中的胶束热力学及聚集行为

采用电导法研究了不同温度下含酯基Gemini表面活性剂在纯水和在质量分数为10%的甲醇-水(MAWR),乙二醇-水(EG-WR),丙三醇-水(GL-WR)四种体系中的集聚行为和胶束热力学;聚集行为参数包括临界胶束浓度(cmc)和抗衡离子的解离程度(α)以及胶束的热力学参数,包括标准吉布斯自由能(ΔG_m~o)、吉布斯迁移自由能(ΔG_(trans)~o)、吉布斯烷基链胶束化自由能(ΔG_(tail)~o)、标准焓变(ΔH_m~o)和标准熵变(ΔS_m~o),均被计算和讨论。研究表明在所有的研究体系中,cmc值随着疏水链的增加而减小,随着加入的醇结构中羟基数目的增加而增大,随温度的升高先变小,后变大呈U字形;胶束化过程都是自发进行的,并且在293.15 K下,胶束化过程是吸热的,在293.15 K上,胶束化过程是放热的;通过稳态荧光光谱法研究了表面活性剂在纯水、有机醇-水混合溶液中的微极性,结果表明,在相同溶剂中,随着烷基链长度的增加,溶液微环境的疏水性越强;对于相同的Gemini表面活性剂,随着加入含羟基数目越多的醇,其微环境的疏水性越强。并研究了Gemini表面活性剂在混合体系中形成胶束过程的焓-熵补偿曲线。     

A method for calculating the Gibbs energies of hydrophobic effects and specific interactions of nonelectrolytes in aqueous solutions

The thermodynamic characteristics of hydrophobic hydration, the Gibbs energies of hydrophobic effect, were calculated. The method for calculations was based on the division of the Gibbs energy of hydration into contributions of nonspecific interactions, specific interactions between solutes and solvents (if they exist), and hydrophobic effect. In the absence of specific interactions between solutes and water, the Gibbs energy of hydrophobic effect depended linearly on the characteristic molecular volume of the solute for substances with different structures and properties. The universality of this dependence allows the suggestion to be made that it remains valid also in the presence of specific interactions. This allows the Gibbs energy of specific interactions in water to be determined for a wide range of compounds, in particular, for aliphatic alcohols.     

Prediction of multicomponent liquid adsorption using excess quantities I. Statistical thermodynamic derivation of the basic equation of excess formalism

The utilization of excess quantities as the basis of a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. From statistical thermodynamics, the fundamental equation is derived for the prediction of ternary or higher order data from adsorption data for the constituent binary mixtures. An additive expression is obtained for the double Gibbs free excess energies, valid for adsorption on liquid mixture/air interfaces as well as liquid mixture/solid interfaces.     

Thermodynamic studies of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol at 25°C

The osmotic coefficients of binary methanol and ethanol solutions of 1-dodecanol and 1-tetradecanol wer measured at 25°C up to 8 mol-kg^–1 in methanol and 5.5 mol-kg^–1 in ethanol. The activity coefficients of the solute were calculated from Bjerrum's relation. From the osmotic and activity coeficients the excess Gibbs energies of solution as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were calculated. In addition, the difference in the Gibbs energy of solvation for the solvent in solution relative to the pure solvent was calculated, as well as the partial molar volumes and excess partial molar volumes of solutes at infinite dilution, and the coefficients of pairwise contributions to the excess volume were determined. The thermodynamic parameters obtained are discussed on the basis of solute-solvent and solute-solute interactions.     

Aggregation behaviour and thermodynamics of mixed micellization of 1-hexadecylpyridinium bromide and ionic liquid in ethylene glycol/water binary mixtures

Micellar behavior of binary combinations of ionic liquid, 1-tetradecyl-3-methylimidazolium bromide, with conventional cationic surfactant 1-hexadecylpyridinium bromide was investigated by means of conductometry to study the effect of cosolvent and water content and temperature. The critical micelle concentration and the degree of counterion association were calculated from the conductometry data. Thermodynamic parameters were obtained from the temperature dependence of the critical micelle concentration. The standard Gibbs energy of micellization increased with the increasing percentage of cosolvent as well as the mole fraction of C₁₄mimBr. The standard enthalpy and standard entropy of micelle formation were both decreased with the increasing temperature and the concentration of cosolvent. The entropy contribution was larger than the enthalpic one in pure water, whereas in the ethylene glycol/H₂O mixture the enthalpy contribution was predominant     

A quasi lattice-local composition model for the excess Gibbs free energy of liquid mixtures

Two new expressions for the excess Gibbs energy of liquid mixtures are derived from Guggenheim's quasi-lattice model and Wilson's local composition concept. These are called the Local Surface Guggenheim equation (LSG) and the Local Composition Guggenheim equation (LCG). The LSG equation is similar, but not identical to UNIQUAC. The new equations require only two adjustable parameters per binary, and no higher-order parameters for extension to multicomponent systems.A critical discussion is given of Guggenheim's quasi-lattice expression for the excess Gibbs energy of athermal mixtures. This expression gives the combinatorial contribution to the new equations.A new method is proposed in the evaluation of the pure component structural parameters, independent of particular assumptions about the lattice parameters.The application of the LSG and the LCG equations to practical problems of phase-equilibria is considered in detail.     

Hierarchical self-organization of perylene bisimide--melamine assemblies to fluorescent mesoscopic superstructures

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB]n nylon-type supramolecular polymers is derived. In addition to the formation of a hydrogen-bonded supramolecular chain. pi-pi interactions were observed for perylene bisimide-melamine assemblies 3b x 8b and 3b x 8c in aliphatic solvents. The orthogonal nature of hydrogen bonding and pi-pi interactions leads to three-dimensional growth yielding large-sized aggregates already in dilute solution. On suitable substrates, densely intertwined networks of nano- to mesoscopic strands are formed which have been investigated by electron microscopy, confocal fluorescence microscopy and optical polarization microscopy. The high fluorescence and excellent photostability of these superstructures is promising for future studies on energy migration and artificial light harvesting at the nano- and mesoscopic length scale.     

Critical parameters of liquid–vapor equilibrium and its geometric interpretation

Expressions are derived for the Gibbs and free energies of a liquid–vapor system. The critical parameters of the liquid are determined, and the character of the relationship between them is found. The temperature dependence of the vaporization heat is found. The analytical expression of the empirical Tait rule is substantiated. General patterns of subcritical and critical equilibria were revealed. A geometric definition of a critical state is proposed, and the existence of two critical states is proven.     

Thermodynamic Analysis of Phase Equilibria in the System Cyclohexane—Methanol

The phase diagram of cyclohexane-methanol was thermodynamically modeledin the range of 150 T/K 360 and at a pressure of 1 bar on the basis ofavailable experimental data. The Gibbs energy functions of four pure solid andtwo mixture phases were taken into consideration. The liquid phase was describedby a model based on mole fraction statistics and the simplified assumption ofmethanol tetramers mixed with cyclohexane monomers. The gas phase was treatedas a nonideal mixture with a Gibbs energy modeled on the basis of the virialcoefficient formalism considering only monomers. The Gibbs energies of the twosolid modifications of pure methanol, as well as pure cyclohexane, were fixedusing literature data. The pressure dependence of the Gibbs energies of the liquidand solid phases were neglected. The complete T-x phase diagram includinggas/liquid equilibria as well as p-x phase diagrams in the range of 20 and 55°C werecalculated. Experimental and calculated data were found to agree reasonably well.     

Solid-fluid and solid-solid phase equilibrium in a model of n-alkane mixtures

Solid-fluid and solid-solid phase equilibrium for binary mixtures of hard sphere chains modeling n-hexane, n-heptane, and n-octane has been calculated using Monte Carlo computer simulations. Thermodynamic integration was used to calculate the Gibbs free energy and chemical potentials in the solid and fluid phases from pure component reference values. A multiple stage free energy perturbation method was used to calculate the composition derivative of the Gibbs free energy. Equation of state and free energy data for the fluid phase indicate ideal solution behavior. Nonideality is much more significant in the solid phase with only partial solubility of shorter chains in the longer chains and essentially no solubility at the other end of the composition range. The miscibility decreases with increasing chain length difference between the components. For the model of n-hexane/n-octane mixtures solid--solid phase separation has been observed directly in some of the simulations, with the components segregating between the layers of the solid structure. The behavior is similar to that seen in some binary n-alkane mixtures with longer chain lengths but comparable chain length ratios between the components. Such phase separation, although indicated thermodynamically, is not seen directly in the simulations of the n-heptane/n-octane mixture due to the difference in the pure component crystal structures.     

Closed-packed lattice model for polymer solution systems considering the chain length dependence effect: Correlating LLE,VLE, and gel swelling behaviors using identical interaction energy parameters

We propose a new Helmholtz energy of mixing equation following the original Flory–Huggins (F–H) closed-packed lattice model. Also, to overcome F–H mean-field approximation, we introduce new universal constants to consider chain length dependence of polymer in solvent and consider specific interactions to describe strongly interacting polymer systems. Our proposed model successfully describes liquid–liquid equilibria (LLE) for binary polymer–solvent systems using identical interaction parameters which do not depend on the polymer molecular weight. We also describe vapor–liquid equilibria (VLE) for polymer/solvent systems and swelling equilibria of thermosensitive hydrogel systems using the same energy parameters obtained from LLE calculations.     

混合胶束中Gemini阳离子表面活性剂14-s-14与常规表面活性剂的协同作用:连接臂及反离子效应(英文)

The mixed micelle formation of binary cationic 14-s-14 gemini with conventional single chain surfactants was studied by conductivity measurements.The critical micelle concentration(cmc) and the degree of counterion binding values(g) of the binary systems were determined.The results were analyzed by applying regular solution theory(RST) to calculate micellar compositions(X),activity coefficients(f1,f2),and the interaction parameters(β).The synergistic interactions of all the investigated cationic gemini+conventional surfactant combinations were found to be dependent upon the length of hydrophobic spacer of the gemini surfactant.The excess Gibbs free energy of mixing was evaluated,and it indicated relatively more stable mixed micelles for the binary combinations.     

The Prediction of Surface Tension and Thermodynamic Analysis of the Surface in Mixtures of Cryogenic Liquids

The surface tensions of 42 binary cryogenic mixtures at low temperature are correlated using the Shereshefsky model and excellent results are obtained. The average percent deviation is about ～ 1.08%. The Gibbs energy change in the surface region is calculated and is used to obtain the excess number of molecular layers in the surface region. Furthermore, the model is used to derive an equation for the standard Gibbs energy of adsorption. The experimental standard Gibbs energy of adsorption is obtained from surface tension data and compared with calculated data. The agreement between experimental and calculated data is found to be very good. The magnitude of the Gibbs energy change in the surface region and the standard Gibbs energy of adsorption are discussed in terms of nature and type of intermolecular interactions in binary mixtures.     

Estimation of infinite dilution activity coefficients in aqueous mixtures via molecular simulation

Molecular dynamics simulations are employed to calculate infinite dilution activity coefficients of water and methanol-like species in binary mixtures using a variant of the Kirkwood coupling parameter method. Differences in residual Gibbs free energies are obtained as integrals over ensemble averages of the derivatives of total potential energy with respect to simple functions of the intramolecular potential energy parameters. The calculated limiting activity coefficients are compared with the experimental values at the same temperature obtained by direct measurement of the water/methanol binary and via extrapolation from vapor–liquid equilibria data.     

Statistical thermodynamics in the framework of the lattice fluid model, 1. Polydisperse polymers of special distribution

The Gibbs free energies and equations of state of polymers with special molar mass distributions, e.g., Flory distribution, uniform distribution and Schulz distribution, are derived based on a lattice fluid model. The influence of the polydispersity (or the chain length) on the close-packed mass density, the close-packed volume of a mer and the mer-mer interaction energy or the scaling temperature is discussed. The diagrams of the Gibbs free energies as a function of temperature and chain length are simulated with a computer. The results suggest that a polydisperse polymer is thermodynamically more stable than the corresponding monodisperse polymer and that the thermodynamical properties of a polydisperse polymer are identical with those of the corresponding monodisperse polymer when the average degree of polymerization is sufficiently high.     

Cloud point measurements of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate with alcohols

Mutual solubility data of imidazolium-based ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([bmmim][BF₄]) with the alcohols, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, and 1-hexanol were obtained by a cloud point method. The upper critical solution temperatures of the ionic liquid and alcohol mixtures were determined from the mutual solubility data. The upper critical solution temperature of the binary mixtures gradually increased as the chain length of the alcohol increased. The mutual solubility data of binary systems ([bmmim][BF₄] + alcohols) have been correlated by the original UNIQUAC model as well as the extended and modified form of the UNIQUAC model. The temperature dependence of the mutual solubility data could be represented in terms of the temperature dependence of the binary energy parameters obtained from the correlation. Additionally the influence of water contamination on the ionic liquid mixture was shown experimentally by adding pure water into the binary mixture ([bmmim][BF₄] + 1-butanol).