Miscibility of Butanol and Cationic Surfactant in the Adsorbed Film and Micelle

Mixed adsorbed films and micelles were investigated by measuring surface tension of the aqueous solutions for the following four mixtures: the n-butanol (NBA)-dodecylammonium chloride (DAC), t-butanol (TBA)-DAC, NBA-dodecyltrimethylammonium chloride (DTAC), and TBA-DTAC. Experimental results were analyzed thermodynamically. Phase diagrams of adsorption and micelle formation and that exhibiting the composition relation of micelle and adsorbed film at CMC were compared among the four systems. Excess Gibbs energy in the adsorbed film gH,E and activity coefficient in the micelle fM2+/- were calculated from the phase diagrams to estimate the miscibility of the butanol and cationic surfactant quantitatively. By comparing the results of the pairs of NBA-DAC and TBA-DAC systems with those of the NBA-DTAC and TBA-DTAC systems, it was shown that the substitution of the polar head group from ammonium to trimethylammonium changes the gH,E value from positive to negative and increases fM2+/-. Furthermore, by comparing the results of the pairs of NBA-DAC and NBA-DTAC systems with those of the TBA-DAC and TBA-DTAC systems, it was shown that the bulky hydrophobic group weakens the molecular interaction between the butanol and the cationic surfactant in the adsorbed film. Copyright 1998 Academic Press.