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Issue 11, 2014
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Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution

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Abstract

Coacervation in an aqueous solution of cationic ammonium gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) with sodium benzoate (NaBz) has been investigated at 25 °C by turbidity titration, light microscopy, dynamic light scattering, cryogenic temperature transmission electron microscopy (Cryo-TEM), scanning electron microscopy (SEM), isothermal titration calorimetry, ζ potential and 1H NMR measurements. There is a critical NaBz concentration of 0.10 M, only above which coacervation can take place. However, if the NaBz concentration is too large, coacervation also becomes difficult. Coacervation takes place at a very low concentration of C12C6C12Br2 and exists in a very wide concentration region of C12C6C12Br2. The phase behavior in the NaBz concentration from 0.15 to 0.50 M includes spherical micelles, threadlike micelles, coacervation, and precipitation. With increasing NaBz concentration, the phase boundaries of coacervation shift to higher C12C6C12Br2 concentration. Moreover, the C12C6C12Br2–NaBz aggregates in the coacervate are found to be close to charge neutralized. The Cryo-TEM and SEM images of the coacervate shows a layer–layer stacking structure consisting of a three-dimensional network formed by the assembly of threadlike micelles. Long, dense and almost uncharged threadlike micelles are the precursors of coacervation in the system.

Graphical abstract: Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution

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Publication details

The article was received on 08 Nov 2013, accepted on 27 Nov 2013 and first published on 02 Dec 2013


Article type: Paper
DOI: 10.1039/C3SM52819G
Citation: Soft Matter, 2014,10, 1705-1713
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    Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution

    R. Wang, M. Tian and Y. Wang, Soft Matter, 2014, 10, 1705
    DOI: 10.1039/C3SM52819G

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