Dynamics of AOT and AOT/nonionic cosurfactant microemulsions. An iodine-laser temperature jump study

Luís M. M. Nazário, João P. S. G. Crespo, Josef F. Holzwarth, T. Alan Hatton

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

The iodine-laser temperature jump (ILTJ) technique was used to probe the interfacial and intermicellar dynamics of water-in-isooctane microemulsions stabilized by AOT both in the presence and in the absence of a cosurfactant such as an aliphatic chained alcohol (hexanol or decanol) or poly(oxyethylene) alkyl ether (C10E4 or C10E8). These cosurfactants have been shown to induce changes in the interfacial rigidity; the former increase it, and the latter decrease it. Two relaxation times were observed, one in the microsecond range and another, previously undetected, in the millisecond range. The relaxation times obtained in the microsecond range were higher for CiEj-containing microemulsions and lower for decanol-containing ones. This is consistent with the effect of the cosurfactants on interfacial rigidity, as this relaxation is inversely proportional to the bending modulus, κ. The value of κ = 0.3 kT determined for AOT reversed micelles (Wo = 55) is in agreement with those found in the literature. The relaxation time in the millisecond range was only obtained above a certain water content and temperature, and its value depended on water content, interfacial composition, and reversed micelle concentration. This relaxation time is discussed in terms of different processes that dominate at different temperatures. At lower temperatures processes relating to the dynamics of the interface are observed, and as temperature is increased reversed micelle coalescence dominates, eventually leading to percolation. The fact that two relaxation times, which are related to interfacial dynamics and to reversed micelle interactions, respectively, can be detected without the need for added electrolyte, probes, or intramicellar reactions is indicative of the potential of ILTJ in the study of these complex systems.

Original languageEnglish
Pages (from-to)5892-5899
Number of pages8
JournalLangmuir
Volume16
Issue number14
DOIs
Publication statusPublished - 11 Jul 2000

Keywords

  • Microemulsions
  • Micelles
  • Micelles RMs

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