Role of the spacer in the non ideal behavior of alkanedyil-α,ω-bis(dodecyldimethylammonium) bromide-MEGA10 binary mixtures

Micellization in the aqueous binary mixtures of n-decanoyl N-methylglucamide, MEGA10, and alkanediyl-α,ω-bis(dodecyldimethylammonium) bromide, 12-s-12 (with s = 7, 9, 11), was investigated at 303 K and the data compared to those previously found in MEGA10-12-s-12 mixed solutions, with s = 2, 3, 4, 5, 6, 8, 10, and 12. Application of different theoretical approaches to the binary mixtures showed a non ideal behavior, the spacer length not affecting substantially the Rubingh interaction parameter. However, circular dichroism experiments show and odd–even effect in the interactions of the dimeric surfactants with MEGA10 molecules within the mixed micelles. Micellar growth was also studied in the mixed micellar solutions, the addition of MEGA10 diminishing the tendency of the dimeric aggregates to form elongated micelles upon increasing surfactant concentration.

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► Mixed MEGA10-12-s-12 micellar solutions were investigated.
► Application of different theoretical approaches shows non ideal behavior.
► Electrostatic interactions are mainly responsible for non ideality.
► Dimeric surfactants with even and odd spacers interact differently with MEGA10.
► Micellar growth was studied in the mixed micellar solutions.