Alkanediyl-α,Ω-bis(dimethylalkylammonium bromide) Surfactanss (Dimeric Surfactants). 5. Aggregation and Microstructure in Aqueous Solutions

D. Danino, Y. Talmon, R. Zana*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

500 Scopus citations

Abstract

A series of alkanediyl-α,Ω-bis(dimethylalkylammonium bromide) surfactants, referred to as dimeric m-s-n surfactants (where m and s are the carbon numbers of the side alkyl chains and of the alkanediyl spacer), have been investigated by time-resolved fluorescence quenching (determination of micelle aggregation number of the 12-S-12 series) and transmission electron microscopy at cryogenic temperature (determination of the nature and shape of the aggregates present in solutions of 12-S-12 and 16-S-16). These m-s-m surfactants can be considered as the dimers of the quarternary ammonium surfactants having two unequal alkyl chains with carbon numbers m and s/2. The 12-S-12 surfactants weee found to form spherical micelles at concentration close to the critical micelle concentration. The homologues with s = 6,8, and 10 showed only a small to moderate micellar growth upon increasing concentration, suggesting that the micelles remained spheroidal in the concentration range investigated. However, the homologues with s = 3, 4, and 5 showed a significant micellar growth, which increased as s decreased. The solutions of 12-2-12 showed shear-thickening at the concentration of 1.4% and became viscoelastic above 2%. Cryo-TEM showed the presence of giant entangled threadlike micelles in the aqueous solutions of this surfactant. Elongated micelles weee also seen in solutions of 12-3-12. Only spherical or spheroidal micelles weee present in solutions of 12-4-12,12-8-12, and 12-12-12, at the concentration investigated, in agreement with the fluorescence quenching results. Vesicles, often double-lamellar weee observed in solutions of 12-16-12 and 12-20-12. Vesicles weee also present in the solutions of the corresponding “monomeric” surfactants. In the case of the 16-S-16 series, vesicles, bilayer membrane fragments and threadlike micelles weee observed in 16-3-16 solutions. Only threadlike micelles weee seen in 16-4-16 solutions, whereas 16-6-16 solutions showed slightly elongated micelles and 16-8-16 solutions spherical micelles. The above results clearly indicate that the dimeric surfactants investigated tend to form in aqueous solutions aggregates of lower curvature than the corresponding “monomeric” surfactants.

Original languageEnglish
Pages (from-to)1448-1456
Number of pages9
JournalLangmuir
Volume11
Issue number5
DOIs
StatePublished - 1 May 1995
Externally publishedYes

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