Y. Moroi et al., SOLUBILIZATION OF ARENES AND N-ALKYLBENZENES INTO IONIC SURFACTANT MICELLES, Colloids and surfaces. A, Physicochemical and engineering aspects, 109, 1996, pp. 201-208
The solubilization of benzene, naphthalene, anthracene and pyrene in a
queous micellar dodecylammonium trifluoroacetate solution (DAPA) and o
f n-alkylbenzenes (benzene to n-pentylbenzene) in 1-dodecanesulfonic a
cid (DSA) solution were measured. The maximum additive concentrations
(MAC) of naphthalene, anthracene, and pyrene and the equilibrium conce
ntrations of the benzenes were determined spectrophotometrically at 29
8.2, 303.2 and 208.2 K for DAPA and at an additional temperature of 29
3.2 K for DSA. The first stepwise association constants ((K) over bar(
1)) between solubilizate monomer and vacant micelle were evaluated fro
m the MAC and the equilibrium concentration, and were found to increas
e with the hydrophobicity of the solubilizate molecules. Standard enth
alpy and entropy changes of the solubilization were obtained from the
temperature dependence of the (K) over bar(1) values, and the location
of these solubilizates in the micelle was discussed thermodynamically
, with the spectra of the solubilizates in solvents of varying dielect
ric constants also being used to compare with the spectra in their sol
ubilized state. The standard entropy changes are negative for the poly
cyclic aromatic compounds, and positive for the n-alkylbenzenes. This
fact indicates that structured water molecules around the alkyl chains
play an important role in their solubilization into micelles, althoug
h quite the same association takes place between micelle and solubiliz
ate for both kinds of solubilizates.