Surface and micellar properties of some amphiphilic drugs in various salt solutions

In this work the effect adding of various electrolytes on the solution properties of three amphiphilic drugs was investigated. The critical micelle concentration (cmc) values, determined on the basis of surface tension measurements, were found to decrease with the increasing salt concentration; this decrease was dependent upon the nature of added ion. Coions (K+ and Na+) remained in the aqueous phase and were almost equally efficient in decreasing the cmc. Counterions (Cl− and Br−) concentrated on the micellar surface and reduced electrostatic repulsion. The smaller the hydrated counterions, the stronger they interacted with the micellar surface. The decrease of cmc was therefore more pronounced for Br− ions than that for Cl− ones. The observed changes in Amin and Γmax were explained in terms of the cmc behavior. The values of both ΔGmpO and ΔGadspO suggest that the drugs tend to form micelles more readily in the presence of salts.