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Counterion spin relaxation in microemulsion droplets

Kenéz, P. Huang; Carlström, G. LU ; Furó, I. and Halle, B. LU (1992) In Journal of Physical Chemistry 96(23). p.9524-9531
Abstract

Counterion 23Na spin relaxation data are reported from the microemulsion phase in the AOT/water/isooctane system as a function of the water/AOT ratio, which determines the size of the aqueous droplets. The 23Na NMR measurements comprise three independent relaxation rates, allowing the individual spectral density values to be determined, as well as the second-order quadrupolar dynamic shift. The effect on the relaxation observables of counterion diffusion within the aqueous droplet core is calculated by solving the diffusion equation in the presence of the electrostatic mean field. This allows the 23Na NMR data to be interpreted in terms of the Na+ lateral diffusion coefficient Ds in... (More)

Counterion 23Na spin relaxation data are reported from the microemulsion phase in the AOT/water/isooctane system as a function of the water/AOT ratio, which determines the size of the aqueous droplets. The 23Na NMR measurements comprise three independent relaxation rates, allowing the individual spectral density values to be determined, as well as the second-order quadrupolar dynamic shift. The effect on the relaxation observables of counterion diffusion within the aqueous droplet core is calculated by solving the diffusion equation in the presence of the electrostatic mean field. This allows the 23Na NMR data to be interpreted in terms of the Na+ lateral diffusion coefficient Ds in the surface region, the residual quadrupole coupling constant χs, and a spectral density contribution Jf due to fast local motions. These quantities have also been determined in a previous 23Na NMR study of the reversed hexagonal phase of the same system, with similar results. Although the present data are basically consistent with the expected microstructure of closed droplets with highly mobile counterfoils, a model of monodisperse spherical droplets cannot account quantitatively for all the data. This discrepancy is tentatively ascribed to the existence of small reversed micelles coexisting with the classical microemulsion droplets.

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organization
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type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry
volume
96
issue
23
pages
8 pages
publisher
The American Chemical Society
external identifiers
  • scopus:1542527694
ISSN
0022-3654
DOI
10.1021/j100202a082
language
English
LU publication?
yes
id
02f3163f-a292-4aed-9154-ca274d13d4bd
date added to LUP
2019-07-25 21:38:38
date last changed
2019-08-19 14:02:11
@article{02f3163f-a292-4aed-9154-ca274d13d4bd,
  abstract     = {<p>Counterion <sup>23</sup>Na spin relaxation data are reported from the microemulsion phase in the AOT/water/isooctane system as a function of the water/AOT ratio, which determines the size of the aqueous droplets. The <sup>23</sup>Na NMR measurements comprise three independent relaxation rates, allowing the individual spectral density values to be determined, as well as the second-order quadrupolar dynamic shift. The effect on the relaxation observables of counterion diffusion within the aqueous droplet core is calculated by solving the diffusion equation in the presence of the electrostatic mean field. This allows the <sup>23</sup>Na NMR data to be interpreted in terms of the Na<sup>+</sup> lateral diffusion coefficient D<sub>s</sub> in the surface region, the residual quadrupole coupling constant χ<sub>s</sub>, and a spectral density contribution J<sub>f</sub> due to fast local motions. These quantities have also been determined in a previous <sup>23</sup>Na NMR study of the reversed hexagonal phase of the same system, with similar results. Although the present data are basically consistent with the expected microstructure of closed droplets with highly mobile counterfoils, a model of monodisperse spherical droplets cannot account quantitatively for all the data. This discrepancy is tentatively ascribed to the existence of small reversed micelles coexisting with the classical microemulsion droplets.</p>},
  author       = {Kenéz, P. Huang and Carlström, G. and Furó, I. and Halle, B.},
  issn         = {0022-3654},
  language     = {eng},
  month        = {01},
  number       = {23},
  pages        = {9524--9531},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry},
  title        = {Counterion spin relaxation in microemulsion droplets},
  url          = {http://dx.doi.org/10.1021/j100202a082},
  volume       = {96},
  year         = {1992},
}