The effect of changing the microstructure of a microemulsion on chemical reactivity

Celia Cabaleiro-Lago, L. Garcia-Rio, P. Hervella

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

A kinetic study was carried out on various solvolytic reactions in water/NH4OT/isooctane microemulsions. The NH4OT surfactant is a derivative of the sodium salt of bis(2-ethylhexyl) sulfosuccinate (NaOT or AOT), where the Na+ counterion has been replaced by NH4+. The counterion substitution effects the phase diagram of the system, and therefore, NH4OT-based microemulsions with high water content reaching values of W = 350 (W = [H2O]/[NH4OT]) can be obtained. The presence of high W values suggests a transition in the microemulsion microstructure from water-in-oil (w/o) to oil-in-water (o/w), as was confirmed by conductivity and H-1 NMR self-diffusion measurements. The interpretation of the kinetic studies in terms of pseudophase formalism allows us to analyze the effect of the microemulsion on chemical reactivity, regardless of its microstructure. It has been confirmed that the values of the solvolytic rate constants at the interphase of oil-in-water microemulsions are similar to those obtained for aqueous SDS systems, showing that the hydration degree of the interphase of the oil-in-water microemulsions is independent of W. The influence of the surfactant counterion on the solvolytic rate constants was analyzed by comparing HOT-, NaOT-, and NH4OT-based microemulsions. An important influence on the rate constants caused by the changes in the structural properties of water has been observed as was confirmed by the water H-1 NMR signals.

Original languageEnglish
Pages (from-to)9586-9595
Number of pages9
JournalLangmuir
Volume23
Issue number19
DOIs
Publication statusPublished - 2007
Externally publishedYes

Swedish Standard Keywords

  • Physical Chemistry (10402)

Keywords

  • Water-in-oil
  • aerosol-ot
  • counterion
  • femtosecond
  • mesostructured fluids
  • reverse micelles
  • solvation dynamics
  • solvolysis
  • sulfosuccinate
  • surfactant

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