Stability of spherical and rod-like micelles of cationic surfactants i
n aqueous salt solutions have been treated on the basis of a statistic
al thermodynamic theory, corrected by incorporation of the micellar su
rface energy term. The modified equations for the double logarithmic r
elationship between micellar aggregation number and ionic strength of
the solution have been derived. The newly derived equations have been
applied to aqueous sodium halides solutions of dodecylpyridinium halid
es including those of chloride, bromide and iodide. Effect of salt con
centration on the degree of ionization and the energy of hydration of
both spherical and rod-like micelles have been demonstrated. Degree of
ionization of the micellar associates decreases with increasing salt
concentration for all surfactants studied. Energy of hydration of both
spherical and rod-like micelles is negative and it increases with inc
reasing salt concentration.