Issue 21, 2012

Hydrophobic counter ion effects on the formation of mesh and reversed phases in the perfluorodecanoate/water system

Abstract

The tetramethylammonium perfluorodecanoate (C10TMA)/water system forms both random, Mh1(0) and correlated mesh, Mh1(R[3 with combining macron]m) phases over a wide range of concentration and temperature. Whilst the random mesh phase is found in the ammonium homologue, the extensive correlated mesh phase seems to be a result of the hydrophobic nature of the tetramethylammonium (TMA) counter ion. In order to explore the reasons for the occurrence of these mesh phases and the effects of hydrophobic counter ions on phase structure the counter ion has been substituted by a series of increasing hydrophobicity namely butyltrimethylammonium (BTMA), dibutyldimethylammonium (DBDMA), and methyltributylphosphonium (MTBP). The phases and their structures were identified by small angle X-ray scattering. Increasing counter ion hydrophobicity causes a change from mesh, to lamellar, and finally to reversed phases. All the hydrophobic counter ions are strongly bound to the water/fluorocarbon interface and, in the case of those with butyl chains, there is penetration of between 50 and 60% of the total number of counter ion methyl groups into the fluorocarbon region of the lamellar phase. These bound counter ions reduce the accessibility of the head group region to solvent water. As the number of butyl chains on the counter ion increases the lamellar phase is progressively lost and is replaced by a reversed micelle phase either as a single phase or as part of an extensive two phase region.

Graphical abstract: Hydrophobic counter ion effects on the formation of mesh and reversed phases in the perfluorodecanoate/water system

Article information

Article type
Paper
Submitted
09 Feb 2012
Accepted
28 Mar 2012
First published
20 Apr 2012

Soft Matter, 2012,8, 5835-5842

Hydrophobic counter ion effects on the formation of mesh and reversed phases in the perfluorodecanoate/water system

R. Zhou, M. Holmes, S. Puntambekar, M. Leaver and R. McCabe, Soft Matter, 2012, 8, 5835 DOI: 10.1039/C2SM25295C

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