B. Hribar and V. Vlachy
Faculty of Chemistry and Chemical Technology, University of Ljubljana,
Aškerčeva 5, 1000 Ljubljana, Slovenia.

ABSTRACT

The Monte Carlo and integral equation results are presented for a primitive
model of a micellar solution. The macroions and small ions are modeled as
charged hard spheres embedded in a continuous dielectric. The ratio of di­
ameters of the macroions and small ions (counterions and co­ions) is 3.0 nm
: 0.4 nm. The macroions are charged with 20 negative charges, the co­ions
have one negative charge, and the counterions may carry one or two positive
charges. In a previous study of solutions containing macroions and counterions
(B. Hribar and V. Vlachy, J. Phys. Chem. B, 1997, 101, 3457­3459) it was
found that in solutions with monovalent counterions (­20:+1) the macroions
were distributed at large distances from each other, while in solutions with
divalent counterions (­20:+2) the macroions shared the layer of counterions.
In the present paper the effects of addition of a simple electrolyte to these
solutions are explored. For systems with monovalent counterions, addition
of a low­molecular weight electrolyte causes the macroions to approach each
other; the first peak of the pair­distribution function is shifted toward smaller
distances. On the other hand, the solutions with divalent counterions seem to
be less affected by addition of a simple electrolyte. The results for the excess
internal energy, and osmotic coefficient for two different macroion concentra­
tions are presented in addition to the structural information.