Abstract
A surface tension study (drop volume method) was performed at 30°C on micellization and adsorbed film formation of a mixed system of a cationic Gemini-type surfactant with a cationic surfactant in comparison with another mixed system of the same Gemini-type surfactant with a nonionic surfactant. The systems studied were Bis-ammonium Gemini derived from tartaric acid dibromide salt [BAGTB, 1,4-Bis(trimethylammonio)-2,3-dodecyloxy butane dibromide] with hexadecyltrimethylammonium bromide (HTAB): BAGTB / HTAB mixed system and with n-decanoyl-N-methylglucamide (MEGA-10): BAGTB / MEGA-10 mixed system. The data of surface tension (γ ) vs logarithmic molality plots as a function of mole fraction of surfactant 2 (2 corresponds to HTAB or MEGA-10), X 2, enabled us to determine the critical micellization concentration (CMC), the surface tension at CMC (γCMC), surface excess concentration (Γt ), the mean molecular surface area (A m), the partial molecular area (PMA), and the measures of efficiency of adsorption (pC20 = -log C20) and CMC / C20 which is available for evaluating the facilitating balance between adsorption and micellization. In addition, a newly defined measure of synergism in surface activity, i.e., the minimum surface Gibbs energy (G (S)min) was employed. Based on these data, the examination of synergism in micelle formation and in surface tension reduction elucidated that the Gemini-type surfactant does not exhibit any positive synergism for either BAGTB / HTAB or BAGTB / MEGA-10 mixed systems. Most of these parameters are found to depend conspicuously on the mixing ratio for both mixtures; indicating that the state of adsorbed film is divided into three ranges of X 2; the lower, the middle and the higher. The compositions of micelles formed at CMC (Y 2) and of adsorbed film (Z 2) equilibinated with bulk solution at a fixed surface tension were estimated.
