Mixtures of monomeric and dimeric surfactants:: Hydrophobic chain length and spacer group length effects on non ideality

Critical micelle concentrations of the C(m)TAB+ 12-s-12 (s = 3, 4, 5 and m = 10, 12, 14, 16) binary systems have been determined, through conductivity and fluorescence measurements, at 298 K. Application of different theoretical approaches to explain mixed micellization shows that non-ideality of the binary systems follows the trend C(16)TAB+12-3-12 < C(14)TAB+12-3-12 < C(12)TAB+12-3-12 < C(10)TAB+12-3-12, and C(12)TAB+125-12 approximate to C(12)TAB+12-4-12 < C(12)TAB+12-3-12. Literature data corresponding to the C(12)TAB+12-2-12, C(12)TAB+m-s-m (s = 2, 4, 6 and m = 12, 14, 16) and TritonX-100+12-s-12 (with s = 3, 6, 12) mixtures were considered in order to investigate the hydrophobic chain length and the spacer group length roles on the observed non ideal behavior. It was found that the capacity of the mixture components to form micelles of similar or different shapes plays a major role in non-ideality.