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Effect of Salt and Surfactant Concentration on the Structure of Polyacrylate Gel/Surfactant Complexes
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.ORCID iD: 0000-0002-0895-1180
2007 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 37, 10959-10964 p.Article in journal (Refereed) Published
Abstract [en]

Small-angle X-ray scattering was used to elucidate the structure of crosslinked polyacrylate gel/dodecyltrimethylammonium bromide complexes equilibrated in solutions of varying concentrations of surfactant and sodium bromide (NaBr). Samples were swollen with no ordering (micelle free), or they were collapsed with either several distinct peaks (cubic Pm3n) or one broad correlation peak (disordered micellar). The main factor determining the structure of the collapsed complexes was found to be the NaBr concentration, with the cubic structure existing up to 150 mM NaBr and above which only the disordered micellar structure was found. Increasing the salt concentration decreases the polyion mediated attractive forces holding the micelles together causing swelling of the gel. At sufficiently high salt concentration the micelle−micelle distance in the gel becomes too large for the cubic structure to be retained, and it melts into a disordered micellar structure. As most samples were above the critical micelle concentration, the bulk of the surfactant was in the form of micelles in the solution and the surfactant concentration thereby had only a minor influence on the structure. However, in the region around 150 mM NaBr, increasing the surfactant concentration, at constant NaBr concentration, was found to change the structure from disordered micellar to ordered cubic and back to disordered again.

Place, publisher, year, edition, pages
2007. Vol. 111, no 37, 10959-10964 p.
National Category
Pharmaceutical Sciences Natural Sciences
URN: urn:nbn:se:uu:diva-96226DOI: 10.1021/jp074112pISI: 000249501700016PubMedID: 17715959OAI: oai:DiVA.org:uu-96226DiVA: diva2:170727
Available from: 2007-09-27 Created: 2007-09-27 Last updated: 2016-04-27Bibliographically approved
In thesis
1. Interaction between Crosslinked Polyelectrolyte Gels and Oppositely Charged Surfactants
Open this publication in new window or tab >>Interaction between Crosslinked Polyelectrolyte Gels and Oppositely Charged Surfactants
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interactions between anionic, crosslinked gels and cationic surfactants have been investigated. When exposed to oppositely charged surfactant, the gel collapses into a dense complex of polyion and micelles. During deswelling, the gel phase separates into a micelle-rich, collapsed surface phase, and a swollen, micelle-free core, both still part of the same network. As more surfactant is absorbed, the surface phase grows at the expense of the core, until the entire gel has collapsed. Polyacrylate (PA) gels with dodecyl- (C12TAB), and cetyltrimethylammonium bromide (C16TAB), as well as hyaluronate gels with cetylpyridinium chloride, have been studied.

Kinetic experiments have been performed on macro- as well as microgels, using micromanipulator assisted light microscopy for the latter. A surfactant diffusion controlled deswelling model has been employed to describe the deswelling. The deswelling kinetics of PA microgels have been shown to be controlled by surfactant diffusion through the stagnant layer surrounding the gel, as the surface phase is relatively thin for the major part of the deswelling. For macroscopic PA gels the surface phase is thicker, and the kinetics with C12TAB were therefore also influenced by diffusion through the surface phase, while for C16TAB they were dominated by it.

Relevant parameters have also been determined using equilibrium experiments. An irregular, balloon-forming deswelling pattern, mainly found for macrogels, as well as unexpectedly long lag times and slow deswelling for microgels, are reported and discussed.

The microstructure of fully collapsed PA/C12TAB complexes has been studied using small-angle X-ray scattering. A cubic Pm3n structure was found at low salt concentration, which melted into a disordered micellar phase as the salt concentration was increased. Further increasing the salt concentration dissolved the micelles, resulting in no ordering.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 68 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 62
Pharmaceutical chemistry, gel, polyelectrolyte, surfactant, deswelling, kinetics, phase separation, volume transition, ion-exchange, diffusion, liquid crystal, SAXS, cubic Pm3n, Farmaceutisk kemi
urn:nbn:se:uu:diva-8216 (URN)978-91-554-6970-2 (ISBN)
Public defence
2007-10-19, B22, BMC, Husargatan 3, Uppsala, 09:15
Available from: 2007-09-27 Created: 2007-09-27Bibliographically approved

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