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Issue 47, 2015
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pH-Regulated surface property and pH-reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

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Abstract

A series of tertiary amide-based gemini surfactants, 2,2′-(1,4-phenylenebis(oxy))bis(N-(3-(dimethylamino)propyl)alkylamide), abbreviated as Cm–A–Cm (m = 8; 10; 12; 14), were synthesized. The surface property and aggregation behaviors of the Cm–A–Cm aqueous solutions were studied in detail. The Cm–A–Cm exhibited high and pH-regulated surface activity at the air/water interface; i.e., the critical micelle concentration was 5.6 × 10−6 mol L−1 at pH = 2.50 when m = 14 and was further regulated to 1.8 × 10−6 mol L−1 by altering the pH to 6.50. When the pH was tuned from 2.0 to 12.0, the appearance of the C12–A–C12 aqueous solution (35 mM) underwent 5 states: transparent water-like solution, viscous fluid, gel-like fluid, turbid liquid and dispersion system with white precipitate. The results of rheology, cryogenic transmission electron microscopy, and dynamic light scattering characterization revealed that the transition from water-like to viscous or gel-like liquid was actually due to aggregate microstructure transition from spherical to worm-like micelles. This transition was completely reversible between pH = 2.50 and 6.81, tuned by adding HCl and NaOH solutions for at least 4 cycles. Similar micellar transitions regulated by pH were also found for m = 8 and 10, whereas only worm-like micelles were formed for m = 14 at both acidic and nearly neutral conditions. Finally, a reasonable mechanism of aggregate behavior transition was proposed from the viewpoint of the molecular states, molecular structures, and the intra- and inter-molecular interactions.

Graphical abstract: pH-Regulated surface property and pH-reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

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Publication details

The article was received on 10 Aug 2015, accepted on 16 Sep 2015 and first published on 16 Sep 2015


Article type: Paper
DOI: 10.1039/C5SM01990G
Citation: Soft Matter, 2015,11, 9135-9143
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    pH-Regulated surface property and pH-reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

    H. Lu, M. Xue, B. Wang and Z. Huang, Soft Matter, 2015, 11, 9135
    DOI: 10.1039/C5SM01990G

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