Mechanism of the Mixed Surfactant Micelle Formation

Abstract

This article provides a full description of the mixed micelle formation process at a molecular level. The mechanism of mixed micelle formation in binary surfactant aqueous solution systems, ionic/nonionic mixed systems (12-2-12/TX-100, 14-2-14/TX-100, and SDS/TX-100), and ionic/ionic mixed systems (12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB), in heavy water solutions was studied by (1)H NMR spectroscopy. The critical micellization concentrations of each individual component in the mixed surfactant solutions were gained by analyzing changes in chemical shift and intensities of resonance peaks. The chemical shift changes indicated that in the 12-2-12/TX-100 and SDS/TX-100 systems, micelles of TX-100 formed first, and then 12-2-12 or SDS molecules were fused in the micelles, respectively, which has been proved by 2D NOESY experiments. In contrast, 14-2-14 was the first component to form the micelles in the 14-2-14/TX-100 system. Although 12-2-12 and 14-2-14 are analogs and differ only in the length of the hydrophobic chain by two methylene groups, they showed different behaviors in the micellization processes in the mixture with TX-100. The observation suggests that in the binary surfactant system under current study, the component with lower cmc in the mixed solution aggregates first; then, the other one fuses, resulting in the mixed micelles as the total concentration increases. The same results were obtained for the ionic/ionic solutions, 12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB. The above results suggest that the two mixed surfactants do not aggregate synchronously. It obviously demonstrates that the so-called "cmc of the mixed surfactant solution" needs reconsideration.

Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters

“…23 To reveal a mechanism of the aggregation, NMR spectroscopy is a suitable method. [48][49][50][51][52] Information on the self-diffusion of boron clusters can be directly obtained from 1 In the case of Na[CoD] -see Figure 2B, there are only single clusters below the CAC (with 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 metallacarboranes fully dissociate in water and counterions are not condensed on the aggregates due to relatively low charge density of bulky metallacarborane cluster, the Na[CoD] aggregates cannot grow beyond a certain limit due to electrostatic restrictions. 20,23 In the case of small boron clusters, we assume that the aggregation number grows with increasing concentration without a limit (see Figure 2A), which resembles the isodesmic association model employed for a self-assembly of dyes, [55][56][57][58] …”

Surfactant–Amino Acid and Surfactant–Surfactant Interactions in Aqueous Medium: a Review

“…The first to report this in a study on three different cationic-anionic surfactant systems were Kaler et al [147]. Mixed surfactant system properties are relatively different from than those of single individual surfactant system [149][150][151][152][153][154][155]. The two different surfactants in a mixed micelle and their interaction may have synergistic or antagonistic effects on the micellization.…”

NMR of liquid crystals and micellar solutions

“…This conclusion implies that the so-called CMC of surfactant mixtures needs reconsideration. 156 Mixtures of hydrogenated and fluorinated surfactants are known to form either mixed or segregated micelles. Furthermore, recent results have highlighted the possibility that intramicellar segregation occurs.…”