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 (γ
CMC), surface excess concentration (Γ
t ), the mean molecular surface area (
A m), the partial molecular area (PMA), and the measures of efficiency of adsorption (pC
20 = -log C
20) and CMC / C
20 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.
View full abstract