Study on the association and phase separation behavior of surfactants and promethazine hydrochloride: impact of ammonium electrolytes

Abstract

In the current study, the association and phase separation of cationic tetradecyltrimethylammonium bromide (TTAB) and nonionic Triton X-100 (TX-100) surfactants with promethazine hydrochloride (PMH) were investigated in aqueous ammonium-based solutions. The micellization nature of the TTAB and PMH drug mixture was examined by evaluating critical micelle concentration (CMC) and counterion binding extent (β) at different salt contents and temperatures (298.15–323.15 K). Micelle formation in the TTAB + PMH mixture was enhanced in the presence of ammonium salts, whereas the process was delayed with an increase in temperature in the respective salt solution. With an increase in salt content, the cloud point (CP) of the TX-100 + PMH mixture decreased, which revealed that the respective progression occurred through the salting out phenomenon. In micellization and clouding processes, the changes in free energies ΔG⁰_m and ΔG⁰_c were found to be negative and positive, respectively, demonstrating that the corresponding processes are spontaneous and non-spontaneous. Standard enthalpies (ΔH⁰_m/ΔH⁰_c) and standard entropies (ΔS⁰_m/ΔS⁰_c) for the association and clouding processes, respectively, were also calculated and discussed. The core forces amid TTAB/TX-100 and PMH in the manifestation of electrolytes are dipole–dipole and hydrophobic forces among the employed components according to the values for ΔH⁰_m/ΔH⁰_c and ΔS⁰_m/ΔS⁰_c, respectively.