Morphological Transition in Fatty Acid Self-Assemblies: A Process Driven by the Interplay between the Chain-Melting and Surface-Melting Process of the Hydrogen Bonds

Abstract : In surfactant systems, the major role of the nature of the counter-ion on the surfactant behavior is well-known. However, the effect of the molar ratio between the surfactant and its counter-ion is less explored in the literature. We investigated the effect of the molar ratio (R) between 12-hydroxystearic acid (12-HSA) and various alkanolamines as a function of the temperature in aqueous solution from the molecular scale to the mesoscale. By coupling microscopy techniques and small angle neutron scattering, we showed that 12-HSA self-assembled into multilamellar tubes and transitioned into micelles at a precise temperature. This temperature transition depended on both the molar ratio and the alkyl chain length of the counter-ion and could be precisely tuned from 20°C to 75°C. This thermal behaviour was investigated by differential scanning calorimetry and wide angle X-ray scattering. We highlighted that the transition at the supramolecular scale between tubes to micelles came from two different mechanisms at the molecular scale as a function of the molar ratio. At low R, with an excess of counter-ion, the transition came from the chain melting phenomenon. At high R, with an excess of 12-HSA, the transition came from both the chain melting process and the surface melting process of the hydrogen bonds. At the mesoscale, this transition of supramolecular assemblies from tubes to micelles, delimited a regime of high bulk viscosity, with a regime of low viscosity.
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Langmuir, American Chemical Society, 2017, 33 (45), pp.12943-12951. 〈10.1021/acs.langmuir.7b02651〉
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Soumis le : mercredi 10 janvier 2018 - 12:12:31
Dernière modification le : mercredi 16 mai 2018 - 11:23:26

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Anne-Laure Fameau, Fabrice Cousin, Arnaud Saint-Jalmes. Morphological Transition in Fatty Acid Self-Assemblies: A Process Driven by the Interplay between the Chain-Melting and Surface-Melting Process of the Hydrogen Bonds. Langmuir, American Chemical Society, 2017, 33 (45), pp.12943-12951. 〈10.1021/acs.langmuir.7b02651〉. 〈hal-01634506〉

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