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Sodium Triflate Decreases Interaggregate Repulsion and Induces Phase Separation in Cationic Micelles

Lima, Filipe S.; Cuccovia, Iolanda M.; Buchner, Richard; Antunes, Filipe E.; Lindman, Björn LU ; Miguel, Maria G.; Horinek, Dominik and Chaimovich, Hernan (2015) In Langmuir 31(9). p.2609-2614
Abstract
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (a), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led... (More)
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (a), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led to a limited increase of the aggregation number, to interface dehydration, and to a progressive decrease in a. The viscosity of DTATf solutions of higher concentration ([DTATf] = 0.06 M) reached a maximum with increasing [NaTf], though the aggregation number slightly increased, and no shape change occurred. We hypothesize that this maximum results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This reduction in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase separation at higher [NaTf]. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
31
issue
9
pages
2609 - 2614
publisher
The American Chemical Society
external identifiers
  • wos:000350918500001
  • scopus:84924402374
ISSN
0743-7463
DOI
10.1021/la5049216
language
English
LU publication?
yes
id
b7140a82-a0d4-4344-9c70-f428e95c7539 (old id 5287892)
date added to LUP
2015-04-24 14:27:23
date last changed
2017-10-08 03:03:05
@article{b7140a82-a0d4-4344-9c70-f428e95c7539,
  abstract     = {Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (a), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led to a limited increase of the aggregation number, to interface dehydration, and to a progressive decrease in a. The viscosity of DTATf solutions of higher concentration ([DTATf] = 0.06 M) reached a maximum with increasing [NaTf], though the aggregation number slightly increased, and no shape change occurred. We hypothesize that this maximum results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This reduction in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase separation at higher [NaTf].},
  author       = {Lima, Filipe S. and Cuccovia, Iolanda M. and Buchner, Richard and Antunes, Filipe E. and Lindman, Björn and Miguel, Maria G. and Horinek, Dominik and Chaimovich, Hernan},
  issn         = {0743-7463},
  language     = {eng},
  number       = {9},
  pages        = {2609--2614},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Sodium Triflate Decreases Interaggregate Repulsion and Induces Phase Separation in Cationic Micelles},
  url          = {http://dx.doi.org/10.1021/la5049216},
  volume       = {31},
  year         = {2015},
}