Journal article
Vibrational spectroscopic study of the structure of sodium bis(2-ethylhexyl)sulfosuccinate reverse micelles and water-in-oil microemulsions
Langmuir, Vol.11(3), pp.738-743
1995
Abstract
The structure of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles and water-in-oil microemulsions in isooctane and cyclohexane has been investigated using vibrational spectroscopy. The formation of reverse micelles resulted in an increase in the interaction between the Na+ counterion and the -SO3 group, compared with the solid state. Hydration of reverse micelles in cyclohexane to form water-in-oil (w/o) microemulsions led to a shift in the wavenumber of the symmetric sulfonate stretching mode from 1064 to 1050 cm-1 in the Raman spectrum and from 1051 to 1045 cm-1 in the infrared spectrum. The difference between the wavenumber of the band maxima in the infrared and Raman spectra, which decreased from 13 to 5 cm-1 after hydration, is attributed to correlation coupling. The splitting of the antisymmetric sulfonate stretching mode in the infrared spectrum, which produces two strong bands at ca. 1212 and 1248 cm-1 in the reverse micelles, is also reduced upon hydration. These results are interpreted in terms of the increase in the separation between the Na+ counterion and the -SO3- group and an associated increase in the separation between the -SO3- groups of adjacent surfactant molecules at the micellar interface. The greatest changes in the interaction between the sulfonate moiety and the sodium counterion occurred below w0 = [H2O]/[AOT] = 3, with only small band shifts in the spectra observed beyond w0 = 6. No shifts were evident beyond ca. w0 = 15. These results are consistent with a strong hydrogen-bonding interaction involving three H2O molecules located between the oxygen atoms of the -SO3- group and a Na+ cation, and the requirement of at least six H2O molecules per AOT molecule to completely solvate the head-group. In contrast, hydration produced only minor changes in the relative infrared intensities of carbonyl stretching modes at ca. 1735 and 1723 cm-1. These observations reflect changes in the relative populations of different conformations about the acyl C-C bond and an increase in the degree of rotation, which accompanies the increase in the average area occupied by the head-group upon hydration.
Details
- Title
- Vibrational spectroscopic study of the structure of sodium bis(2-ethylhexyl)sulfosuccinate reverse micelles and water-in-oil microemulsions
- Authors
- P D Moran (Author) - Australian Nuclear Science and Technology Organisation Materials DivisionG A Bowmaker (Author) - Australian Nuclear Science and Technology Organisation Materials DivisionR P Cooney (Author) - Australian Nuclear Science and Technology Organisation Materials DivisionJohn R Bartlett (Author) - Australian Nuclear Science and Technology Organisation Materials DivisionJ L Woolfrey (Author) - Australian Nuclear Science and Technology Organisation Materials Division
- Publication details
- Langmuir, Vol.11(3), pp.738-743
- Publisher
- American Chemical Society
- Date published
- 1995
- DOI
- 10.1021/la00003a012
- ISSN
- 0743-7463
- Organisation Unit
- School of Science and Engineering - Legacy; University of the Sunshine Coast, Queensland
- Language
- English
- Record Identifier
- 99448709102621
- Output Type
- Journal article
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- Collaboration types
- Domestic collaboration
- International collaboration
- Web Of Science research areas
- Chemistry, Multidisciplinary
- Chemistry, Physical
- Materials Science, Multidisciplinary