Micellization of sodium dodecyl sulfate with a series of nonionic n-alkyl malono-bis-N-methylglucamides in the presence and absence of gelatin

The critical micelle concentrations (cmc's) for binary mixtures of sodium d odecyl sulfate (SDS) and nonionic n-alkyl malono-bis-N-methylglucamides (C( n)BNMG) have been measured by surface tension. Synergistic interactions ove r the entire mole fraction range are observed when the nonionic alkyl chain length n is either 10 or 12, A switch from antagonistic behavior at low SD S solution mole fractions to synergistic behavior at high SDS solution mole fractions is observed for the C(14)BNMG/SDS mixture. The dodecyl sulfate u nimer concentrations in binary mixtures of C(12)BNMG/SDS are well described by regular solution theory (Rubingh, D. N. Solution Chemistry of Surfactan ts; Plenum: New York, 1979) using the experimentally determined cmc values: On addition of gelatin, the cmc is depressed for the binary C(10)BNMG/SDS and C(12)BNMG/SDS combinations, but only above a critical SDS solution mole fraction, alpha (critical)(SDS). Therefore, interaction between the gelati n and the mixed micelles is only seen above alpha (critical)(SDS). No corre sponding alpha (critical)(SDS) value is found for the C(14)BNMG/SDS system. Here, cmc's are unchanged by the presence of gelatin for any mixture, thus indicating no interaction between the mixed C(14)BNMG/SDS Critical increas es. For the micelle and gelatin. On increasing the nonionic alkyl chain len gth from 10 to 12, "sDs latter system where both components possess dodecyl tails, the dodecyl sulfate unimer concentration is reduced for solutions a bove alpha (critical)(SDS) but remains unchanged for solutions below alpha (critical)(SDS), relative to the no-gelatin case. The composition of the bo und micelle is very different from that formed in the absence of gelatin. F urthermore, whereas the compositions of the micelle and solution are vastly different in the absence of gelatin, they are very similar in the presence of gelatin. Not only does the nonionic surfactant promote binding of SDS t o gelatin, but at the highest SDS mole fraction studied, it induces pre-cmc (1) nonmicellar SDS binding.