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Vesicular Phase Behaviour in Ionic Surfactant Systems with Organic Counter-ions

Vesikulares Phasenverhalten in ionischen Tensidsystemen mit organischen Gegenionen
R. Friman, S. Backlund, C. V. Teixeira and M. Linden

Abstract

Phase diagrams at 298.2 K were determined for aqueous systems of alkylamines and alkanoic acids in equimolecular ratio, i.e. for alkylammonium alkanoates. The bilayer structural evolution for these ionic surfactants with organic counter-ions in water was studied using transmission electron microscopy (TEM), optical microscopy, small-angle X-ray scattering (SAXS) and rheological measurements. The formed vesicles are highly viscoelastic and have a yield stress value. In the pentylammonium nonanoate-water system at higher contents, the vesicles collapse to micelles, while in the hexylammonium nonanoate-water and in the pentylammonium decanoate systems, a transition to a fully expressed lamellar phase is observed. The results are discussed in terms of electrostatic interactions and membrane flexibility.

Kurzfassung

Phasendiagramme wässriger Systeme von Alkylaminen und Alkansäuren, d.h. für Alkylammoniumalkonate, wurden bei 298,2 K in gleichmolekularem Verhältnis bestimmt. Für diese Tenside mit organischen Gegenionen in Wasser wurde die strukturelle Entwicklung der Doppelschicht mittels Transmission-Elektronenmikroskopie (TEM), optischer Mikroskopie, Kleinwinkelröntgenstreuung (SAXS) und rheologischer Messungen studiert. Die ausgebildeten Vesikel sind hoch viskoelastisch und haben eine ausgeprägte Fließspannung. Im Pentylammoniumnonanoat-Wasser-System zerfallen die Vesikel bei höherem Gehalt, während im Hexylammoniumnonanoat-Wasser-System und im Pentylammoniumdecanoat-Wasser-System ein Übergang zu einer voll ausgebildeten lamellaren Phase beobachtet wird. Die Ergebnisse werden bezüglich ihrer elektrostatischen Wechselwirkungen und Membranflexibilität diskutiert.


Dr. Rauno Friman, Åbo Akademi University, Department of Physical Chemistry, Porthaninkatu 3-5, FI-20500 Turku, Finland. E-mail:

Rauno Friman studied chemistry at Åbo Akademi University and obtained his PhD in 1983. He presently works as a lecturer at Åbo Akademi, Finland. His research interests include aggregation and phase structures in surfactant systems.

Sune Backlund studied chemistry at Åbo Akademi University and obtained his PhD in 1979. 2003 he has retired from the lectureship at Åbo Akademi University.

Cilâine Verônica Teixeira studied Physics at the University of São Paulo and obtained her PhD in 1999. She presently works at Åbo Akademi University as a post-doc. Her research interests include the study of micellar solutions, liquid crystals and mesoporous materials and small-angle x-ray scattering.

Mika Lindén studied chemistry at the Abo Akademi University and obtained his PhD degree in 1996. He is presently working as a group leader at the department of Physical Chemistry at the same university. His research interests are sol-gel chemistry, surfactant chemistry, kinetic particle nucleation and growth studies, and controlled drug release.


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Received: 2005-07-07
Published Online: 2013-04-05
Published in Print: 2006-03-01

© 2006, Carl Hanser Publisher, Munich