Adsorption and Micellization Behavior of Cationic Surfactants (Gemini and Conventional)-Amphiphilic Drug Systems

In the present work, the behavior of mixed drug-surfactant systems has been studied by surface tension measurements. The drug used in this work is adiphenine hydrochloride (ADP) and the surfactants are of m-s-m type geminis, i.e., alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide), with m = (14, 16), s = (4, 5, 6), and conventional alkyltrimethylammonium bromides (CTAB, TTAB). The excess surface concentration (I" (max) ) increases and the minimum head group area at the air/water interface (A (min)) decreases with increasing concentration of surfactant in the drug solution. Both the critical micelle concentration (cmc) and ideal cmc (cmc*) values decrease with mole fraction of surfactants. Also, the cmc values are lower than cmc*, indicating attractive interactions are present in the mixed micelles. The mole fractions of surfactant in the micelles and monolayers , as well as the respective interaction parameters (, ), indicate that monolayer formation is easier than micelle formation due to the rigid hydrophobic part of the drug.