Recommended data for the limiting activity coefficients (gamma(infinity)(1)) of nitrobenzene, aniline, and cyclohexylamine in water were established as a function of temperature by the simultaneous correlation of the values resulting from specialized vapor-liquid equilibrium measurements and related thermal data for highly dilute solutions. The new values of gamma(infinity)(1) were determined by the Rayleigh distillation, circulation still, and headspace analysis methods. The limiting partial molar excess heat capacities were derived from measurements by the Picker flow microcalorimetry. These values were combined with all available literature data on the limiting activity coefficients and the limiting partial molar excess enthalpies. This allowed us to produce a thermodynamically consistent fit of gamma(infinity)(1) between 273 K and 373 K, which was in turn used in combination with pure solute vapor pressures to calculate the Henry's law constants (k(H)).

Aiming to probe their aggregative properties in solution, an extensive thermodynamic study of aqueous solutions of some poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) block copolymers (pluronics) was carried out for concentrations up to 20% w/w in the temperature interval 288.15-328.15 K. For dilute solutions of pluronics L31, L35, L64, F68, P123 and 10R5, density measurements were performed at 298.15 and 318.15 K, and heat capacities were determined at 298.15 K. From these data accurate partial molar volumes and heat capacities at infinite dilution are obtained. They are compared with calculated values using group-contribution additive schemes for monomeric repeating units. It is concluded that experimental values are sensitive to the structural state of the pluronic in solution. Depending on either the molar mass and the PO/EO ratio of the pluronic or the temperature, the following different structural states are present in solution: dispersed monomers, mixed monomers micelles species and predominantly micelles. The aqueous solutions of L31, L64 and P123 were selected for a more detailed study of densities between 288.15 and 328.15 K, and of sound speeds between 288.15 and 308.15 K. Using these experimental data, apparent molar volumes, isobaric molar expansibilities and isentropic compressibilities were calculated and their concentration and temperature dependence were derived. From the analysis of changes in these properties, thermally induced transitions are shown and related to the hydrophobic character of the pluronic. Apparent molar expansibilities, heat capacities and the temperature dependence of isentropic compressibilities are shown to be very sensitive to the aggregation process. From their sharp maxima in transition regions a clear relationship between critical micelle concentrations and critical micelle temperatures is obtained.

Excess molar volumes and isobaric excess molar heat capacities for {1,3-dioxolane + 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol} and excess molar enthalpies for the binary mixtures {1,3-dioxolane: + 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol} at the temperature 298.15 K have been determined as a function of mole fraction. The results are discussed in terms of structural changes on mixing and of the nature of intermolecular interactions in these solutions.

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.

A Picker flow microcalorimeter was employed in conjunction with asymmetric syringe-type pumps to measure heats of mixing of highly dilute aqueous solutions of organic solvents. These data were used in turn to determine limiting partial molar excess enthalpies of the examined solvents in water. The measurements were carried out at 298.15 K for 29 common, oxygen and/or nitrogen containing solvents exhibiting complete miscibility with water. Except for only one compound, formamide, the limiting partial molar excess enthalpies are exothermic indicating that the process of dissolution is energetically favored. Comparison to literature data (in most cases to solution enthalpies at infinite dilution measured by batch calorimetry) proved the technique applied to be sufficiently accurate.

The densities and the ultrasonic speeds of the aqueous solutions of 2-(2-hexyloxyethoxy)ethanol (C6E2) were measured over the entire range of mole fractions at 5°C. Excess molar volumes V E were readily calculated from the densities. The densities, in combination with the ultrasonic speeds, furnish estimates of the molar (and excess molar) isentropic compressibilities K S and the deviations u D of the ultrasonic speeds from the values calculated for ideal mixtures. Radical changes in the mole fraction derivatives of the excess molar properties of the (C6E2 + water) system, in the vicinity of an amphiphile mole fraction of 0.003, indicate that C6E2 like C6E3 is capable of micelle formation. Our data have been compared with those reported earlier for (C4E2 +, C2E2 +, and C6E3 + water). We have employed both mass action and pseudophase approaches to data analysis, together with the four-segment model approach.

Densities and apparent molar heat capacities of some alkylated derivatives of uracil and adenine: 1-methyluracil, 1,3-dimethyluracil, 1,3-diethylthymine, 5,6-trimethylene-1,3-dimethyluracil, 5,6-tetramethylene-1,3-dimethyluracil, 5,6-pentamethylene-1,3-dimethyluracil, 2,9-dimethyladenine, 2-ethyl-9-methyladenine, 2-propyl-9-methyladenine, 8-ethyl-9-methyladenine, 6,8,9-trimethyladenine and 8-ethyl-6,9-dimethyladenine were determined using flow calorimetry and flow densimetry at 25°C. It was found that the partial molar volumes and heat capacities correlate linearly with the number of substituted methylene groups-CH 2 -as well as to the number of hydrogen atoms, n H , belonging to the skeleton of the molecule. In the case of alkylated uracils a difference was observed in the values at infinite dilution V 2 o and C p2 o , depending on the substitution of alkyl and cyclooligomethylene groups.

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.

Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermodynamic properties of alkyldimethylamine oxides in water. Application of a mass-action model for micellizationJacques E. Desnoyers, Gaston Caron, Rosario DeLisi, David Roberts, Alain Roux, and Gerald PerronCite this: J. Phys. Chem. 1983, 87, 8, 1397–1406Publication Date (Print):April 1, 1983Publication History Published online1 May 2002Published inissue 1 April 1983https://pubs.acs.org/doi/10.1021/j100231a024https://doi.org/10.1021/j100231a024research-articleACS PublicationsRequest reuse permissionsArticle Views277Altmetric-Citations167LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The microemulsion formed by water + sodium dodecylsulfate + n-butanol + toluene has been investigated through precise heat capacity measurements. The weight ratio of sodium dodecylsulfate to n-butanol was kept constant at 1:2. Taking toluene as a molecular probe its apparent molal heat capacity φc4 was used to follow the changes in structure over the whole miscibility region of the pseudoternary phase diagram. Large changes in φc4 are observed in the aqueous end. On the other hand, changes are much more gradual as the composition tends to pure toluene. Similar trends were recently observed for volumes for the same system. Some of the changes in structure proposed by other authors for this system are confirmed by the present study and their limits better defined.

It has been claimed by Enderby and co-workers that changes in long-range order occur in NiCl2 aqueous solutions at high concentrations. To investigate the possibility of a transition, the partial molar heat capacities and volumes of NiCl2, CaCl2, MgCl2, and NaCl were measured and compared in water at 25 °C up to 6 mol kg−1. In the case of NaCl, data were also measured at 5 and 45 °C. A slight change in slope of [Formula: see text] is observed for NiCl2 around 4 mol kg−1 which may suggest a third or higher order transition. However, the change is too small to support unambiguously any particular model for the high concentration region.

The conditions under which the Picker flow microcalorimeter can be used to measure enthalpies and rates of reactions were investigated. For this purpose, systematic studies were made of the enthalpies of neutralization of HCl, HBr, HNO 3 , acetic, proprionic, and butyric acids with NaOH, enthalpies of hydrolysis of methyl and ethyl acetate with NaOH, and the reaction rates of the ester hydrolysis with NaOH. The general procedure and various sources of error are discussed and it is concluded that enthalpies of slow reactions can be measured to about 1% when the calorimeter is operated in the quasi-isothermal mode and the reaction rates to about 3% when operated in the quasi-adiabatic mode.

Measurements at 25 °C with flow calorimeters and densimeters have led to heat capacities and densities of aqueous solutions of 11 1:1 electrolytes: NaClO3, NaBrO3, NaIO3, NaNO3, NaClO4, NH4NO3, KClO3, KBrO3, KIO3, NH4Cl, and NH4ClO4. The first 6 salts were studied up to near saturation. We have used results of these measurements to obtain apparent molal heat capacities and apparent molal volumes of the various solutes. Extrapolation to infinite dilution on the basis of the Debye–Hückel theory bas led to [Formula: see text]and [Formula: see text] values for each solute. We have compared these standard values with results of earlier investigations.