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NMR Relaxation in Micelles Formed by a Long Zwitterionic Surfactant

Söderman, O. LU ; Carlström, G. LU orcid ; Monduzzi, M. and Olsson, U. (1988) In Langmuir 4(4). p.1039-1044
Abstract

A frequency-dependent 14N and 13C NMR relaxation study of the micellar region formed by a very long zwitterionic surfactant, viz., 6-(dimethyleicosylammonio)hexanoate (C20AH), is presented. As a starting point the binary phase diagram of C20AH/D2O is determined. The phase diagram is similar to those found for shorter chain ionic surfactants with bulky head groups. The NMR relaxation data show a dependence upon the magnetic field strength and are discussed in terms of the two-step model of relaxation. The frequency dependence found at low frequencies in the 14N data is assumed to be caused by the rotational tumbling of the micelle, while it is argued that the frequency... (More)

A frequency-dependent 14N and 13C NMR relaxation study of the micellar region formed by a very long zwitterionic surfactant, viz., 6-(dimethyleicosylammonio)hexanoate (C20AH), is presented. As a starting point the binary phase diagram of C20AH/D2O is determined. The phase diagram is similar to those found for shorter chain ionic surfactants with bulky head groups. The NMR relaxation data show a dependence upon the magnetic field strength and are discussed in terms of the two-step model of relaxation. The frequency dependence found at low frequencies in the 14N data is assumed to be caused by the rotational tumbling of the micelle, while it is argued that the frequency dependence found at high frequencies in the 13C relaxation data is caused by a local motion. The analysis of the data yields a radius of the micelle which is slightly shorter than an extended C20 chain, pointing to a situation where the methylene groups in the head-group dipole are embedded in the micelle. Moreover, the local motions in the head-group region are slow as compared to the corresponding motions in single-chain ionic surfactants.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
4
issue
4
pages
6 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:0040376627
ISSN
0743-7463
DOI
10.1021/la00082a039
language
English
LU publication?
yes
id
d8f97df9-9e00-433d-8265-c61c34304bb0
date added to LUP
2019-07-25 21:40:20
date last changed
2022-03-29 02:34:14
@article{d8f97df9-9e00-433d-8265-c61c34304bb0,
  abstract     = {{<p>A frequency-dependent <sup>14</sup>N and <sup>13</sup>C NMR relaxation study of the micellar region formed by a very long zwitterionic surfactant, viz., 6-(dimethyleicosylammonio)hexanoate (C<sub>20</sub>AH), is presented. As a starting point the binary phase diagram of C<sub>20</sub>AH/D<sub>2</sub>O is determined. The phase diagram is similar to those found for shorter chain ionic surfactants with bulky head groups. The NMR relaxation data show a dependence upon the magnetic field strength and are discussed in terms of the two-step model of relaxation. The frequency dependence found at low frequencies in the <sup>14</sup>N data is assumed to be caused by the rotational tumbling of the micelle, while it is argued that the frequency dependence found at high frequencies in the <sup>13</sup>C relaxation data is caused by a local motion. The analysis of the data yields a radius of the micelle which is slightly shorter than an extended C<sub>20</sub> chain, pointing to a situation where the methylene groups in the head-group dipole are embedded in the micelle. Moreover, the local motions in the head-group region are slow as compared to the corresponding motions in single-chain ionic surfactants.</p>}},
  author       = {{Söderman, O. and Carlström, G. and Monduzzi, M. and Olsson, U.}},
  issn         = {{0743-7463}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{4}},
  pages        = {{1039--1044}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Langmuir}},
  title        = {{NMR Relaxation in Micelles Formed by a Long Zwitterionic Surfactant}},
  url          = {{http://dx.doi.org/10.1021/la00082a039}},
  doi          = {{10.1021/la00082a039}},
  volume       = {{4}},
  year         = {{1988}},
}