Enthalpies of solution in sodium octanoate + water + alcohol mixtures

Abstract

Enthalpies of solution of sodium octanoate in water, 1-propanol and aqueous mixtures of l-propanol, 1-butanol, 1-pentanol and 1-hexanol, and of the alcohols in aqueous solutions of sodium octanoate at various concentrations were determined calorimetrically at 35 ~ Most AH(soln) values are exothermic and strongly dependent on the solute concentration. The main energetic factor governing the process of dissolution of the surfactant is associated with changes in the water structure caused by the presence of alcohol. That governing the process of the alcohol dissolution in surfactant solutions is due to the effect alcohols have on the CMC of the octanoate. There is no indication of the alcohol being either solubilized in the interior of the aqueous micelle, or becoming part of the micellar film.The solubility at 35 ~ of sodium octanoate in water, 1-propanol and their mixtures has also been determined. In the previous reports [1][2][3][4] in these series the calorimetrically determined enthalpies of solution in some model ternary colloidal systems have been interpreted in terms of solute-solvent interactions between the components. We believe we have provided considerable evidence to show that the energetics of solubilities in such simpler systems -which can be regarded as limiting cases for the more complex, four-component microemulsion -are helpful in understanding the balance of forces which define microemulsion stability. In this balance of forces the role of the alcohol cosurfactant is perhaps the most complex one. Namely, the hydrophilic -hydrophobic balance of a microemulsion is governed primarily by the extent of water or oil miscibility of the alcohol cosurfactancThe presence of any third component in aqueous solutions of ionic surfactants is known to have an effect on the micellar properties of the binary solutions. With an aliphatic alcohol as the third component the effect is generally due to any single one or a combination of the basic processes characterized as (i) the change in the solvent structure, (ii) the solubilization of the alcohol in the interior of the aqueous micelle, and (iii) the incorporation of the alcohol molecules into the O 849 micelles in the form of mixed micellar films. A separate identification of these effects is by no means trivial. Methanol or ethanol are considered to affect micelle formation by virtue of their effect on the solvent structare, and no micelles of ionic surfactants are formed in mixed aqueous solutions containing 30-40 volume percent of the alcohols [5]. Propanol and higher alcohols, which are known microemulsion cosurfactants, in contrast to methanol or ethanol, have apparently no such dramatic effect on the micellization process per se, though the degree of surfactant aggregation is probably lowered [6][7][8]. However, since their presence affects many of the overall properties of aqueous micellar solutions [9][10][11][12], even more than methanol or ethanol do, it is usually assumed that other interactions play a more important role.In an attempt t...

Surfactant partitioning in cloud droplet activation: a study of C8, C10, C12 and C14 normal fatty acid sodium salts

“…Instead, we therefore used the largest concentrations reported by Campbell and Lakshminarayanan (1965) as solubility limits for each of the fatty acid sodium salts studied. These limiting concentrations decrease in order of increasing carbon chain length as expected for the water solubilities of the fatty acid sodium salts (Wen et al, 1998) and the values for sodium caprylate and sodium myristate are comparable to the water solubilities reported by Kertes et al (1985) and Wen and Franses (2000).…”

“…Water solubilities for sodium caprylate and sodium myristate have been reported as approximately 0.5 kg kg −1 (Kertes et al., 1985) and 0.002 kg kg −1 (Wen and Franses, 2000), respectively. To the best of our knowledge, no literature values are available for the corresponding water solubilities of sodium caprate and sodium laurate.…”

Thermodynamics of microemulsion formation. 1. Enthalpy of solution of water in binary (Triton X 100 + butanol) and ternary (heptane + Triton X 100 + butanol) mixtures and heat capacity of the resulting systems

“…and (Cp)ceic decrease with «/ 6+ ; the calculated heat capacities are fairly lower than the corresponding experimental values (Table I). The difference, 19.1 (25.5) 22.4 (29.0) 21.6 (28.5) 22.3 (30.0) 26.6 (33.0) 23.3 (33.0) 26.3 (37.0) 27.3 (39.0) 25.6 (37.0) 24.5 (37.0) 26.7 (40.0) 25.0 (38.0) 23.9 (42.0) 15.9 (42.0) 18.0 (43.0) 8.9 (33.5) 12.4 (47.8) 10.1 (44.3) 78.0 (74.0) 71.8 (70.0) 70.0 (70.0) 66.8 (68.0) 64.4 (65.0) 61.0 (64.0) 57.5 (60.0) 52.7 (57.0) 54.0 (59.0) 51.0 (58.0) 48.6 (55.0) 48.1 (56.0) 39.8 (50.8) 30.5 (45.0) 20.5 * Standard deviation of (Cp)"bs ±4.6%.6 s + cs composition, 1:1 ratio (w/w).…”