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Issue 1, 2006
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Freezing transitions in mixed surfactant/alkane monolayers at the air–solution interface

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Abstract

Mixed monolayers at the air–water interface of the cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), with alkanes show a first-order freezing transition as a function of temperature. Sum-frequency spectra and ellipsometric measurements are consistent with a structure in which the high-temperature phase is liquid-like and the low-temperature phase has all-trans, upright chains. There are strong structural similarities between the low-temperature phase in the mixed monolayers and frozen monolayers at the alkane–air and alkane–CTAB solution interfaces. The difference between the surface freezing point Ts and the freezing point of the bulk alkane Tb ranges from 1 °C for alkane chain length m = 17, to 28 °C for m = 11. Surface freezing is more favourable in mixed monolayers at the air–water interface than at the bulk alkanewater interface for the same surfactant concentration. Long-chain alkanes do not wet water, but it is postulated that if they did, they would also show surface freezing analogously to alkanes on silica. The surfactant plays the dual role of enhancing wetting and surface freezing of the alkane on water.

Graphical abstract: Freezing transitions in mixed surfactant/alkane monolayers at the air–solution interface

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Article information


Submitted
15 Aug 2005
Accepted
26 Oct 2005
First published
14 Nov 2005

Soft Matter, 2006,2, 66-76
Article type
Paper

Freezing transitions in mixed surfactant/alkane monolayers at the air–solution interface

K. M. Wilkinson, L. Qunfang and C. D. Bain, Soft Matter, 2006, 2, 66
DOI: 10.1039/B511561B

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