O/W Emulsion of n-Alkylbenzene/Ionic Surfactant/Water Systems

Abstract

The maximum additive concentration of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene into two kinds of ionic micelles, 1-dodecanesulfonic acid and n-tetradecyltrimethylammonium bromide micelles, was determined at 298.2 K, where these volatile solubilizates were solubilized, not by direct contact of the liquid solubilizate with micellar solution but by molecular transfer through their own gaseous phase. The aggregation number of micelles is ca. 60 and their size is 5 nm in diameter in the aqueous solution in the case of no solubilizate in the system. In the presence of the above solubilizates, however, the micellar aggregates greatly grow in size up to more than 150 nm in diameter for 1-dodecanesulfonic acid micelle and 200 nm for n-tetradecyltrimethylammonium bromide micelle, where the micelles or the aggregates accommodate the volatile solubilizates as much as possible or the maximum additive concentration. The solubilization was analyzed by partition equilibrium of the solubilizates between aqueous phase and micellar phase, because the micelles are so large in size. The contribution per ethylene group in the alkyl chain to the Gibbs energy change was calculated to be −2.35 and −2.78 kJ mol-1 for 1-dodecanesulfonic acid and n-tetradecyltrimethylammonium bromide micelles, respectively. The larger negative value for the latter is due to more hydrophobic solubilization site by hydrocarbon head of the latter.