Alfredo Amigo

Refractive indices, molar volumes and molar refractions of binary liquid mixtures: concepts and correlations

Prompted by the observation that recent literature displays marked disagreement as to the proper treatment of data on the refractive indices of binary liquid mixtures, this paper clarifies the relationships among refractive index, molar volume and molar refraction and the corresponding mixing properties. It is shown that the molar refraction deviation function must be calculated on a mole fraction basis and the refractive index deviation function on a volume fraction basis, which makes it directly interpretable as a sign-reversed measure of the deviation of reduced free volume from ideality.

Application of the Prigogine-Flory-Patterson model to excess volumes of mixtures of tetrahydrofuran or tetrahydropyran with cyclohexane or toluene

Abstract Excess molar volumes V E m at the temperatures 288.15 K, 298.15 K and 308.15 K and normal atmospheric pressure of binary mixtures of tetrahydrofuran or tetrahydropyran with cyclohexane or toluene have been computed from density measurements. From the results, the thermal expansion coefficients, α, were estimated. The Prigogine-Flory-Patterson theory and its applicability in predicting V E m is tested.

Refractive indexes of binary mixtures of tetrahydrofuran with 1-alkanols at 25°C and temperature dependence of n and ρ for the pure liquids

Refractive indexes at 25°C were measured for binary mixtures of tetrahydrofuran with 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol. Densities, from which excess molar volumes were derived, were measured at the same temperature for the system tetrahydrofuran + 1-decanol. Refractive indexes and densities for the pure compounds were determined at 11 temperatures between 20 and 30°C. The thermal expansion coefficients and the temperature derivatives of the refractive index for these liquids were calculated at 25°C. The temperature dependence of the molar refraction was also examined. The contribution to the molar refraction of a CH2 group was calculated as was the difference between contributions from CH3 and CH2OH groups. The change of molar refraction on mixing is d iscussed in terms of molecular interactions and alkyl chain length.

Prediction of excess volumes and excess surface tensions from experimental refractive indices

Abstract Refractive indices for the binary liquid mixtures: {hexane or heptane + ethanol}, {o-xylene + benzene} and {cyclohexane + benzene, toluene or hexane} were measured at 298.15 K. Excess refractive indices were calculated and fitted to a Redlich-Kister function. Using some mixture rules (Lorentz-Lorenz, Dale -Gladstone, Eykman, Oster, Arago-Biot and Newton), predictions for vE have been made and compared with experimental data taken from the literature. Furthermore the Sugden equation has been used in two different ways for predicting excess surface tensions: the first one starting from densities and the other one from refractive indices. Results are plotted together with the literature data.

Densities and Viscosities of the Binary Mixtures Decanol + Some n-Alkanes at 298.15 K

Abstract Densities and viscosities of four binary liquid systems decanol +n-heptane, +n-octane, +n-nonane, +n-decane, have been determined at 298.15 K and atomospheric pressure, over the complete composition ranges. The excess values of molar volume, viscosity and Gibbs free energy for the activation of flow were evaluated. The Grunberg-Nissan parameter was also calculated. The viscosity data were fitted to the equations of McAllister and Auslander.

Thermodynamic properties of binary mixtures of 2-hexanone withn-alkanes at 35°C

Excess molar enthalpies hE and excess molar volumes vE of the binary liquid mixtures 2-hexanone+n-alkane (from n-heptane to n-decane) have been determined for various values of the mole fraction of hexanone at 35°C and atmospheric pressure. Excess molar enthalpies were determined by Calvet microcalorimetry and vE from densities measured by vibratingtube densimetry. The results are compared with the predictions of several group contribution models.

A small molecular size system giving unexpected surface effects: α-Cyclodextrin + sodium dodecyl sulfate in water

Maximum drop volumes (MDV) and the resultant surface tension values (sigma) of alpha-cyclodextrin (alpha-CD) + sodium dodecyl sulfate (SDS) aqueous mixtures have been determined over a broad concentration range of both solutes at 283.15, 293.15, 303.15, 313.15, and 323.15 K. Drops significantly larger than those of pure water (up to approximately 25% larger) were observed at low temperatures for solutions with [alpha-CD]/[SDS] concentration ratios, approximately > 2, producing unexpectedly high surface tension values. Our results indicate that at certain solute concentration ratios and temperatures, the drop volume method provides wrong values for equilibrium surface tensions. This is due to the high viscoelasticity of the surface film whose effect is important even though the injection rate of the drops was slow and the solutes molecular sizes are small.

Excess molar volumes of (o-xylene + n-heptane + toluene or n-hex-1-ene) at the temperature 298.15 K

Excess molar volumes at the temperature 298.15 K of ( o -xylene + n -heptane), ( o -xylene + toluene), ( o -xylene + n -hex-1-ene), ( n -heptane + toluene), ( n -heptane + n -hex-1-ene), ( o -xylene + n -heptane + toluene), and ( o -xylene + n -heptane + n -hex-1-ene) have been determined from density measurements. Variable-degree polynomials have been fitted to the results.

STAND: Surface Tension for Aggregation Number Determination

Taking advantage of the extremely high dependence of surface tension on the concentration of amphiphilic molecules in aqueous solution, a new model based on the double equilibrium between free and aggregated molecules in the liquid phase and between free molecules in the liquid phase and those adsorbed at the air/liquid interface is presented and validated using literature data and fluorescence measurements. A key point of the model is the use of both the Langmuir isotherm and the Gibbs adsorption equation in terms of free molecules instead of the nominal concentration of the solute. The application of the model should be limited to non ionic compounds since it does not consider the presence of counterions. It requires several coupled nonlinear fittings for which we developed a software that is publicly available in our server as a web application. Using this tool, it is straightforward to get the average aggregation number of an amphiphile, the micellization free energy, the adsorption constant, the maximum surface excess (and so the minimum area per molecule), the distribution of solute in the liquid phase between free and aggregate species, and the surface coverage in only a couple of seconds, just by uploading a text file with surface tension vs concentration data and the corresponding uncertainties.

Excess molar enthalpies of (n-decan-1-ol + an n-alkane) at the temperatures 298.15 K and 308.15 K

The excess molar enthalpies of { x CH 3 (CH 2 ) 8 CH 2 OH + (1 − x )CH 3 (CH 2 ) m −2 CH 3 } for m = 7 to 10, have each been determined experimentally as a function of the mole fraction x at the temperatures 298.15 K and 308.15 K and normal atmospheric pressure using a Calvet microcalorimeter. Two methods of correlating the results are examined.