Abstract
The energetics of clouding in amphiphilic drugs, promazine hydrochloride and nortriptyline hydrochloride, in the presence of additives, such as alcohols and surfactants, are reported. The additives which assist in micellar growth like long-chain alcohols and cyclohexanol give negative Delta H-s(0) and T Delta S-s(0) values, whereas cationic and nonionic surfactants increase the randomness in the system and hence T Delta S-s(0) becomes positive. Anionic surfactants at low concentrations retard micellar growth and hence on increasing the concentration T Delta S-s(0) values change from positive to negative.