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Phase behavior of an ionic surfactant with mixed monovalent/polymeric counterions

Svensson, Anna LU ; Piculell, Lennart LU ; Karlsson, Lisa LU ; Cabane, B and Jönsson, Bo LU (2003) In The Journal of Physical Chemistry Part B 107(32). p.8119-8130
Abstract
A "complex salt" of cetyltrimethylammonium (CTA(+)) with short (30 repeating units) polyacrylate (PA(-)) counterions has been synthesized. The phase diagrams of its aqueous mixtures with either the surfactant cetyltrimethylammonium acetate (CTAAc), or the polyelectrolyte NaPA, have been studied by visual inspection through crossed polarizers and by small-angle X-ray scattering. Both of the ternary phase diagrams are strikingly simple, containing only micellar, cubic micellar, and hexagonal phases. In the CTAPA/CTAAc/water system, the surfactant forms essentially spherical micelles above ca. 50 wt % of water, regardless of the counterion composition, and the system may serve as a model for charged colloids with mixed monovalent/polymeric... (More)
A "complex salt" of cetyltrimethylammonium (CTA(+)) with short (30 repeating units) polyacrylate (PA(-)) counterions has been synthesized. The phase diagrams of its aqueous mixtures with either the surfactant cetyltrimethylammonium acetate (CTAAc), or the polyelectrolyte NaPA, have been studied by visual inspection through crossed polarizers and by small-angle X-ray scattering. Both of the ternary phase diagrams are strikingly simple, containing only micellar, cubic micellar, and hexagonal phases. In the CTAPA/CTAAc/water system, the surfactant forms essentially spherical micelles above ca. 50 wt % of water, regardless of the counterion composition, and the system may serve as a model for charged colloids with mixed monovalent/polymeric counterions. The interactions between micelles varies from repulsive to attractive as the fraction of monovalent counterions is dec

eased. This results, first, in a liquid-liquid phase separation between a concentrated branch and a dilute branch of the micellar phase and, finally, a crystallization of micelles into a cubic (Pm3n) phase in equilibrium with essentially pure water. Small fractions of polymeric counterions "melt" the cubic phase. This is attributed to heterogeneity: A small proportion of micelle pairs that share polymeric counterions experience strong attractions. In CTAPA/NaPA/water mixtures, the micelle-micelle interactions switch from attractive to repulsive as the NaPA content is increased. A similar effect occurs with added NaAc. Monte Carlo simulations of interactions between surfactant aggregates neutralized by mixed polymeric and monovalent counterions qualitatively reproduce all experimental trends and show that the dominating source of the attraction between the aggregates is polyion bridging. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
107
issue
32
pages
8119 - 8130
publisher
The American Chemical Society
external identifiers
  • wos:000184665000019
  • scopus:0041878553
ISSN
1520-5207
DOI
10.1021/jp027275g
language
English
LU publication?
yes
id
49dad94b-7449-4b26-a82e-492450a9362d (old id 122223)
date added to LUP
2007-07-12 12:06:53
date last changed
2017-07-23 04:47:26
@article{49dad94b-7449-4b26-a82e-492450a9362d,
  abstract     = {A "complex salt" of cetyltrimethylammonium (CTA(+)) with short (30 repeating units) polyacrylate (PA(-)) counterions has been synthesized. The phase diagrams of its aqueous mixtures with either the surfactant cetyltrimethylammonium acetate (CTAAc), or the polyelectrolyte NaPA, have been studied by visual inspection through crossed polarizers and by small-angle X-ray scattering. Both of the ternary phase diagrams are strikingly simple, containing only micellar, cubic micellar, and hexagonal phases. In the CTAPA/CTAAc/water system, the surfactant forms essentially spherical micelles above ca. 50 wt % of water, regardless of the counterion composition, and the system may serve as a model for charged colloids with mixed monovalent/polymeric counterions. The interactions between micelles varies from repulsive to attractive as the fraction of monovalent counterions is dec<br/><br>
eased. This results, first, in a liquid-liquid phase separation between a concentrated branch and a dilute branch of the micellar phase and, finally, a crystallization of micelles into a cubic (Pm3n) phase in equilibrium with essentially pure water. Small fractions of polymeric counterions "melt" the cubic phase. This is attributed to heterogeneity: A small proportion of micelle pairs that share polymeric counterions experience strong attractions. In CTAPA/NaPA/water mixtures, the micelle-micelle interactions switch from attractive to repulsive as the NaPA content is increased. A similar effect occurs with added NaAc. Monte Carlo simulations of interactions between surfactant aggregates neutralized by mixed polymeric and monovalent counterions qualitatively reproduce all experimental trends and show that the dominating source of the attraction between the aggregates is polyion bridging.},
  author       = {Svensson, Anna and Piculell, Lennart and Karlsson, Lisa and Cabane, B and Jönsson, Bo},
  issn         = {1520-5207},
  language     = {eng},
  number       = {32},
  pages        = {8119--8130},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Phase behavior of an ionic surfactant with mixed monovalent/polymeric counterions},
  url          = {http://dx.doi.org/10.1021/jp027275g},
  volume       = {107},
  year         = {2003},
}