Micellization of Sodium Dodecyl Sulfate with a Series of Nonionic n-Alkyl Malono-bis-N-methylglucamides in the Presence and Absence of Gelatin

Abstract

The critical micelle concentrations (cmc's) for binary mixtures of sodium dodecyl sulfate (SDS) and nonionic n-alkyl malono-bis-N-methylglucamides (CnBNMG) have been measured by surface tension. Synergistic interactions over 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 SDS solution mole fractions to synergistic behavior at high SDS solution mole fractions is observed for the C14BNMG/SDS mixture. The dodecyl sulfate unimer concentrations in binary mixtures of C12BNMG/SDS are well described by regular solution theory (Rubingh, D. N. Solution Chemistry of Surfactants; Plenum: New York, 1979), using the experimentally determined cmc values. On addition of gelatin, the cmc is depressed for the binary C10BNMG/SDS and C12BNMG/SDS combinations, but only above a critical SDS solution mole fraction, . Therefore, interaction between the gelatin and the mixed micelles is only seen above . No corresponding value is found for the C14BNMG/SDS system. Here, cmc's are unchanged by the presence of gelatin for any mixture, thus indicating no interaction between the mixed C14BNMG/SDS micelle and gelatin. On increasing the nonionic alkyl chain length from 10 to 12, increases. For the latter system where both components possess dodecyl tails, the dodecyl sulfate unimer concentration is reduced for solutions above but remains unchanged for solutions below , relative to the no-gelatin case. The composition of the bound micelle is very different from that formed in the absence of gelatin. Furthermore, 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 to gelatin, but at the highest SDS mole fraction studied, it induces pre-cmc(1) nonmicellar SDS binding.