K. Hamada et al., Ionic strength effects of electrolytes on solubilized states of water in AOT reversed micelles, J COLL I SC, 233(2), 2001, pp. 166-170
The limiting amounts of solubilized aqueous NaCl, NaNO3, MgC1(2), and AlCl3
in sodium 1,2-bis-(2-ethylhexyloxycarbonyl)-1-ethanesulfonate (aerosol OT)
/isooctane solutions have been measured as a function of the ionic strength
of the electrolytes. In any system, the limiting amounts increased up to t
he optimal ionic strength (Io(opt)), and afterward, as ionic strength incre
ased, they decreased and were followed by a constant. These increased and d
ecreased curves of water solubilization below and above Io(opt) called, res
pectively, salting-in and salting-out curves, could be interpreted, respect
ively, from the counteracting effects of attractive intermicellar interacti
on and interfacial bending stress. The effects of electrolytes on the solub
ilized states of water by micelles were examined using NMR and near-infrare
d spectroscopic techniques. Consequently, two types of waters, i.e., water
bound directly to the ionic head groups of the surfactant in reversed micel
les and water interacting with the hydrated head groups in swollen micelles
through hydrogen bonds, were almost unaffected by any electrolytes, wherea
s much greater effects were observed for bulklike water in W/O microemulsio
ns. The order of the degree of lowering of salting-out curves in W/O microe
mulsion regions in each system was found to agree with the Hofmeister serie
s. (C) 2001 Academic Press.