A Cloud Point Study on the Micellar Growth of an Amphiphilic Drug in the Presence of Alcohol and Ionic Surfactant

Cloud point (CP) measurements have been performed to investigate the influence of alcohols (C2-C10OH) on the micellar growth of amphiphilic drug amitriptyline (AMT) in the presence of salt and surfactant. In the case of shorter-chain alcohols (C4OH or C5OH), the CP increased with increasing alcohol concentration in the presence of a small amount of sodium phosphate because they partition very little in AMT micelles. On the other hand, it steeply decreased with increasing alcohol concentration in the case of longer-chain alcohols (C8OH or C10OH) due to their considerable partitioning in AMT micelles. The effect of hindering the micellar aggregation was enhanced as the alcohol chain length increased in the case of shorter-chain alcohols. The CP became less sensitive to addition of C6OH at higher sodium phosphate concentrations, resulting from incorporation of more C6OH molecules into the enlarged micelles. Addition of cationic surfactant cetylpyridinium chloride to the AMT micellar solutions increased the CP because cetylpyridinium cations affect electrostatic interactions with the cationic AMT headgroup, while addition of anionic surfactant, sodium dodecyl sulfate, decreased the CP because of penetration of dodecyl chains into the micelles, resulting in a micellar growth