Gérard Douhéret

Isentropic compressibilities : Experimental origin and the quest for their rigorous estimation in thermodynamically ideal liquid mixtures

In this review, attention is initially focused upon the evolution of the Newton-Laplace Equation, that links the measured speed of sound in a fluid in conjunction with its density, to a reliable estimate of its isentropic compressibility κS. Definitions of ideal and excess isentropic quantities are formulated on the premise that the thermodynamic properties of an ideal mixture are mutually related in the same manner as are those of a real mixture or a pure substance. It is shown that both intensive and extensive properties can be derived from the ideal Gibbs energy. Different approaches previously used to calculate ideal isentropic quantities are examined and some subtle errors are identified. The consequences of using conflicting definitions are pointed out. Isentropic pressure derivatives obtained under different conditions and empirical models for estimating the differences between ultrasonic speeds in real and ideal liquid mixtures are discussed.

Ultrasonic speeds and isentropic functions of (a 2-alkoxyethanol + water) at 298.15 K

Abstract Ultrasonic speeds have been measured in (2-methoxyethanol + water), (2-ethoxyethanol + water), and (2-butoxyethanol + water) at 298.15 K, across their entire composition ranges. Their values have been combined with those of the molar volumes to obtain estimates of the product of the molar volume and the isentropic compressibility. The values that were obtained for the excess molar quantities are analysed using a segmented-composition model.

Aggregative processes in aqueous solutions of isomeric 2-butoxyethanols at 298.15 K

Ultrasound speed measurements across the entire composition range of aqueous mixtures of both isobutoxyethanol (iC4E1) and tert-butoxyethanol (tC4E1) have been made at 298.15 K with a sonic solution monitor that employs a “pulse–echo–overlap” technique. In addition, densities of aqueous mixtures of tC4E1 were determined using a vibrating tube densimeter. These new data were complemented with literature values for densities of aqueous mixtures of tC4E1 and for densities and sound speeds of aqueous mixtures of n-butoxyethanol (nC4E1). In all cases, density values were converted to molar volumes, Vm, and excess molar volumes, VmE. Estimates of the isentropic molar compression, KS,m [= −(∂Vm/∂p)S], and of its excess counterpart, KS,mE, were obtained from the combination of the ultrasound speeds and density values. Data reduction procedures were used to generate consistent sets of values for thermodynamic properties of isomeric amphiphiles with increasing degree of alkyl branching. The graphs for the composition dependence of excess partial molar volumes and isentropic compressions of water show enhanced visual impact. These graphs are used for presenting evidence for identifying the prevailing patterns of molecular aggregation. Segmented-composition models, including a version onto which a mass action component has been grafted, are employed, together with a simplified pseudo-phase model, to analyse the various excess molar quantities. The experimental evidence thus obtained is used to relate the effect of chain branching with the degree of self-aggregation of amphiphiles in aqueous solution. An unexpectedly low self-aggregation among iC4E1 molecules is found and discussed in terms of vicinity to the lower critical solution temperature.

Shape transitions in the aqueous phase of the system hexadecyltrimethylammonium bromide—hexanol—water

Abstract Viscosity, conductivity, density, and ultrasonic velocity measurements have been used to characterize aqueous solutions of hexadecyltrimethylammonium bromide and hexanol, i.e., the L 1 phase of the system. At surfactant molalities below 0.055 m , conductivity and ultrasonic velocity measurements show that a change in the solubilization pattern takes place as hexanol is added. It seems that above a certain hexanol content, the additive is solubilized not only in the palisade layer but also in the interior of the micelles, thus producing swollen micelles. The viscosity remains practically constant as hexanol is added. At surfactant molalities above 0.055 m the relative viscosity increases drastically above a certain hexanol content and the conductivities show a maximum at this point. This suggests a shape transition from spherical to larger rod- or disklike micelles. At surfactant molalities between 0.055 and 0.09 m hexadecyltrimethylammonium bromide, the viscosities start to decrease at even higher hexanol contents. The conductivity and ultrasonic velocity measurements also show that a change in solubilization pattern takes place at this hexanol content. It seems likely that hexanol becomes solubilized in the micellar interior and that a breakdown from large aggregates to spherical swollen micelles takes place. It seems that the L 1 phase of the system hexadecyltrimethylammonium bromide—hexanol—water can be divided into four structurally different regions; one of monomeric species, one of ordinary spherical micelles, one of swollen spherical micelles, and one of rod- or disklike micelles.

THERMODYNAMIC PROPERTIES OF (ETHAN-1,2-DIOL + WATER) AT THE TEMPERATURE 298.15 K. I, MOLAR VOLUMES, ISOBARIC MOLAR HEAT CAPACITIES, ULTRASONIC SPEEDS, AND ISENTROPIC FUNCTIONS

Densities have been measured in (ethan-1,2-diol + water) at the temperatures 288.15 K, 298.15 K, 303.15 K, and 308.15 K, across the entire composition range. Isobaric expansivities were derived from the results. Measurements have also been made of the isobaric heat capacities divided by volume and of the ultrasonic speeds, at the temperature 298.15 K, over the whole composition range. The values of these two properties have been combined with the molar volumes to obtain estimates of the products of the molar volume and the isentropic compressibility and of the molar volume and the isentropic expansivity. The values that were obtained for the excess molar quantities have been analysed using a segmented-composition model.

Excess molar volumes and enthalpies of the 2-butoxyethanol + water system at 25° C

Abstract Excess molar volumes and excess molar enthalpies have been measured for the 2-butoxyetanol + water system at 25° C, across the total composition range. The data have been used as a vehicle for modifying the parameterization of the four-segment model equations and for examining the effects of various constraints upon the flexibility of the model. The results of the analyses are consistent with the formation of pseudomicellar aggregates.

Aggregative processes in aqueous solutions of mono- to tetra-ethylene glycol dimethyl ether at 298.15 K

A sonic solution monitor that employs the “pulse-echo-overlap” technique was used to measure ultrasound speeds in binary liquid mixtures of water with mono- to tetra-ethylene glycol dimethyl ether (also known as mono- to tetra-glyme) across their entire composition ranges. In addition, densities of aqueous mixtures of ethylene glycol dimethyl ether (monoglyme) were determined using a vibrating tube densimeter. The new data were complemented with literature values for the densities of aqueous mixtures of di-, tri- and tetra-glyme. All measurements were made at 298.15 K. Densities were converted to excess molar volumes, VEm. Combination of the densities and ultrasound speeds provided estimates of the excess molar isentropic compressions, KES,m. The excess thermodynamic properties were converted to excess partial and apparent molar properties of both components of each mixture. Negative values are generally observed for all of the excess molar properties. Graphs are presented to exhibit the effects of extending the length of the polyether chain. Data analyses have been carried out using different versions of the four-segment model for aqueous mixtures of amphiphile substances, one version of which including a mass action component. At a given composition in the transitional segment, it is found that the investigated excess molar properties become approximately insensitive to the chain length in the glyme molecules. Present and previously reported VEm data have been combined for constructing series showing the effect of replacing successively the hydroxyl hydrogens in ethan-1,2-diol by methyl groups, as well as increasing the number of ethylene oxide units in 2-methoxyethanol. Along these series of aqueous mixtures, negative excess molar volumes are found to increase in magnitude. Limiting partial molar volumes and isentropic compressions are reported for the glymes in water and for water in the glymes.

Speeds of sound and excess volumetric properties of mixtures of water with ethylene glycol monopropyl ether at 298.15 K

Abstract Densities and ultrasonic speeds of binary mixtures of water with ethylene glycol monopropyl ether have been measured at 298.15 K over the entire composition range. Estimates of the isentropic molar quantity, K s , equal to −( ∂ V/ ∂p ) s , and of its excess counterpart, K s E , were obtained from the density values, in combination with those of the ultrasonic speed. Our results have been compared with those reported earlier for 2-propanol +, and ethylene glycol monoisopropyl ether + water systems, and with literature data relative to the 1-propanol + water system. The various excess molar quantities have been analyzed using segmented-composition models, including a version onto which a mass action component has been grafted.

Patterns of molecular aggregation in aqueous mixtures of species of the type CmE2m+1 · (OC2H4)n · OH: Part 1. Applications of an empirical model to some CmE0 plus water systems

Abstract A rationale is given for the four-segment composition approach to the analysis and interpretation of the thermodynamic properties of binary amphiphile plus water systems. The hypothesis is introduced that there exist, within isotropic binary water plus amphiphile mixtures, labile patterns of molecular aggregation which resemble the more stable schemes that are observed in water plus non-ionic detergent systems. The nature of such patterns of molecular aggregation varies from one composition range to another in a manner which is reflected by changes in the composition dependence of the macroscopic properties. A new version of the four-segment model equations was devised to explore, in more detail, the nature of the composition dependence of thermodynamic properties in that composition segment which corresponds to a range of varying micellar geometries.

Thermodynamics of aqueous mixtures of 2-(2-Hexyloxyethoxy)ethanol at 5°C

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 VE were readily calculated from the densities. The densities, in combination with the ultrasonic speeds, furnish estimates of the molar (and excess molar) isentropic compressibilities KS and the deviations uD 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.