Abstract
Mixed micellization and mixed adsorbed film formation were investigated for the combination of a Gemini type cationic and a nonionic surfactants mixture: Bis-trimethyl ammonium Gemini derived from tartaric acid bromide (BAGTB) and n-Decanoyl-N-methylglucamide (MEGA-10). The surface tension of the aqueous mixed surfactant solution was measured at every 0.1 mole fraction of MEGA10 in the surfactant mixture applying a drop volume method at 30°C. From the curves of surface tension (γ) vs logarithmic concentration in molality (ln m ), critical micellization concentration (CMC), minimum surface tension at CMC (γCMC), surface excess (Γ), mean surface area occupied by a molecule (A m) and parameters related to synergism in surface activity such as pC20 and CMC / C20 were determined. Based on the regular solution theory, the relation of compositions of the singly dispersed phase (X MEGA10) and the micellar phase (Y MEGA10), and the relation of X MEGA10 with the composition in adsorbed film phase (Z 2) were estimated, and along with these, the interaction parameters in micelles (ωR) and in adsorbed film (ωA ) were calculated. Both the CMC-X MEGA-10 and CMC-Y MEGA-10 curves showed a negative deviation from ideal mixing and even the curve of Z MEGA10-m t (bulk phase concentration) produced a slightly negative ωA . However, the synergism in surface tension reduction was found to be rather weak from examination of partial molecular area (PMA) and the minimum free energy at surface G min(S) = (γCMC·A m·L ). As for the adsorbed film, the interaction mode between molecules, as well as two dimensional molecular packing, was observed to be separated into three regions; i. e. at X STDS = 0.45 and at X STDS = 0.75 different properties changed discontinuously.
