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Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases

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Abstract

A homologous series of n-alkyl trimethylammonium bromide surfactants, H(CH2)nN+(CH3)3 Br, from C10TAB to C18TAB have been studied systematically in the bulk over a wide range of temperatures. Common features in the structures are identified, with packing dominated by the co-ordination of the cationic head groups with bromide anions and interdigitation of the hydrocarbon chains. This arrangement provides an explanation for the thin adsorbed bilayers that have been observed at various hydrophilic surfaces from aqueous solutions in previous studies. The molecular volumes and arrangement are comparable with structures of a number of different self-assembled amphiphiles. For these surfactants with bromide counter-ions, formation of crystal hydrates was not observed. The alkyl chains are highly mobile and at high temperatures a plastic phase is found for all materials with a transition enthalpy that is similar to the melting enthalpy of many long alkyl chains. Other unexpected phase transitions depend more markedly on the hydrocarbon chain length and evidently depend on delicate balances of the various contributions to the free energy.

Graphical abstract: Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases

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Publication details

The article was received on 13 Aug 2019, accepted on 24 Sep 2019 and first published on 25 Sep 2019


Article type: Paper
DOI: 10.1039/C9CP04486H
Phys. Chem. Chem. Phys., 2019, Advance Article
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    Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases

    J. K. Cockcroft, A. Shamsabadi, H. Wu and A. R. Rennie, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C9CP04486H

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