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Growth behavior, geometrical shape, and second CMC of micelles formed by cationic gemini esterquat surfactants
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2015 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 16, 4644-4653 p.Article in journal (Refereed) Published
Abstract [en]

Micelles formed by novel gemini esterquat surfactants have been investigated with small-angle neutron scattering (SANS). The growth behavior of the micelles is found to differ conspicuously depending on the length of the gemini surfactant spacer group. The gemini surfactant with a long spacer form rather small triaxial ellipsoidal tablet-shaped micelles that grow weakly with surfactant concentration in the entire range of measured concentrations. Geminis with a short spacer, on the other hand, form weakly growing oblates or tablets at low concentrations that start to grow much more strongly into polydisperse rodlike or wormlike micelles at higher concentrations. The latter behavior is consistent with the presence of a second CMC that marks the transition from the weakly to the strongly growing regime. It is found that the growth behavior in terms of aggregation number as a function of surfactant concentration always appear concave in weakly growing regimes, while switching to convex behavior in strongly growing regimes. As a result, we are able to determine the second CMC of the geminis with short spacer by means of suggesting a rather precise definition of it, located at the point of inflection of the growth curve that corresponds to the transition from concave to convex growth behavior. Our SANS results are rationalized by comparison with the recently developed general micelle model. In particular, this theory is able to explain and reproduce the characteristic appearances of the experimental growth curves, including the presence of a second CMC and the convex strongly growing regime beyond. By means of optimizing the agreement between predictions from the general micelle model and results from SANS experiments, we are able to determine the three bending elasticity constants spontaneous curvature, bending rigidity, and saddle-splay constant for each surfactant.

Place, publisher, year, edition, pages
2015. Vol. 31, no 16, 4644-4653 p.
Keyword [en]
Agglomeration, Cationic surfactants, Esters, Micelles, Neutron scattering, Aggregation numbers, Esterquat surfactants, Geometrical shapes, Low concentrations, Precise definition, Spontaneous curvature, Surfactant concentrations, Worm-like micelles
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-166971DOI: 10.1021/acs.langmuir.5b00742ISI: 000353864200008ScopusID: 2-s2.0-84928667815OAI: diva2:814773

QC 20150608

Available from: 2015-05-28 Created: 2015-05-21 Last updated: 2015-06-08Bibliographically approved

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Bergström, Lennart Magnus
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