Physicochemical Properties of Amphiphilic Drug and Anionic Surfactant Mixtures: Experimental and Theoretical Approach

Herein, we have reported the mixed micelle formation of amphiphilic phenothiazine drug promethazine hydrochloride (PMT) and anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) mixtures at different compositions and temperatures (288.15, 293.15, 298.15, 303.15, and 308.15 K). A conductometric method is used to evaluate the critical micelle concentration (CMC) of binary mixtures. An attractive interaction between PMT and AOT mixed systems was indicated by the experimental and ideal critical micelle concentration (CMC and CMCid) values. The micellar mole fraction of anionic surfactant (, , , and ) was evaluated by different proposed models, and they prove the greater contribution of AOT in mixed micelle and increase with the increase in AOT concentration. Activity coefficients (f 1 and f 2) calculated by all recommended models were found to be always less than unity, signifying nonideality in the mixed systems. Different thermodynamic parameters have also been evaluated using the respective CMC values as a function of temperature. values were always found to be negative for all the systems; however, for pure drug as well as PMT–AOT mixed systems is negative at lower temperatures and positive at higher temperatures. The values are positive at all temperatures but their magnitude is higher at T = 303.15 K and above.