8546
Langmuir 2004, 20, 8546-8551
Determination of Pore Size of Catanionic Icosahedral Aggregates Karine Glinel,*,† Monique Dubois,‡,§ Jean-Marc Verbavatz,| Gleb B. Sukhorukov,‡ and Thomas Zemb*,§ “Polyme` res, Biopolyme` res, Membranes”, UMR 6522 CNRS - Universite´ de Rouen, F-76821 Mont Saint Aignan, France, Max Planck Institute of Colloids and Interfaces, Interfaces Department, D-14476 Golm/Potsdam, Germany, Service de Chimie Mole´ culaire, CEA/DSM/DRECAM, CE Saclay, F-91191 Gif-sur-Yvette, France, and Service de Biophysique des Fonctions Membranaires DSV/DBJC, CEA/Saclay, F-91191 Gif-sur-Yvette, France Received March 15, 2004. In Final Form: July 19, 2004 We show that it is possible to measure the porosity of facetted micron-sized hollow icosahedra of catanionic solutions by performing fluorescence recovery after photobleaching measurements. The size of spontaneous permanent pores in bilayers formed via molecular segregation is compatible with what is observed by freeze-fracture electron microscopy and is discussed versus theoretical expressions of bending energy.
Introduction In the absence of salt, mixtures of single-tailed anionic and cationic surfactants produce so-called catanionic aggregates resulting from electrostatic interactions between oppositely charged headgroups.1 Lamellar phases, stiff nanodisks, cylindrical micelles, and facetted vesicles are present in the room-temperature triangular cut of the ternary phase prism.2 The association of cationic and anionic surfactants produces bilayers with variable charge per unit area and hence allows a direct and unique measurement of intermolecular forces between bilayers of controlled surface charge in the domain -30 to +30 µC/cm2.3 In the presence of salt formed by a combination of counterions, quaternary systems including at least one hydrophobic counterion such as tosylate spontaneously form multilamellar vesicles in equilibrium with lamellar phases at maximum swelling.4 A particular type of catanionic system is obtained by mixing the corresponding acid and hydroxide surfactants: The counterions react to form a water molecule so that, in salt-free conditions, a salt-free system is produced.5,6 A common, but yet unexplained, feature of all catanionic systems studied so far is their surprisingly low aptitude to encapsulate water-soluble molecules. A review on all available data related to this surprisingly quick release of solutes once encapsulated in catanionic globular or facetted vesicles has been published.7 * To whom correspondence should be addressed. K. Glinel: e-mail,
[email protected]; fax, 00 33 2 35 14 67 04. † “Polyme ` res, Biopolyme`res, Membranes”, UMR 6522 CNRS Universite´ de Rouen. ‡ Max Planck Institute of Colloids and Interfaces, Interfaces Department. § Service de Chimie Mole ´ culaire, CEA/DSM/DRECAM, CE Saclay. | Service de Biophysique des Fonctions Membranaires DSV/ DBJC, CEA/Saclay. (1) Pa¨ivi, J.; Bengt, J.; Eichmu¨ller, B.; Fontell, K. Langmuir 1988, 4 (1), 187. (2) Zemb, Th.; Dubois, M. Aust. J. Chem. 2003, 56, 971. (3) Meister, A.; Dubois, M.; Belloni, L.; Zemb, Th. Langmuir 2003, 19, 7259. (4) Kaler, E. W.; Herrington, K. L.; Murthy, A. K.; Zasadzinski, J. A. J. Phys. Chem. 1992, 96, 6698. (5) Dubois, M.; Zemb, Th. Book of Abstracts, 215th ACS National Meeting, Dallas, Mar 29-Apr 2, 1998; American Chemical Society: Washington, DC, 1998. (6) Dubois, M.; Gulik-Krzywicki, Th.; Deme´, B.; Zemb, Th. C. R. Acad. Sci. 1998, IIC, 567.
The equilibrium phase diagram of the mixture of tetradecanoic acid, so-called myristic acid, and cetyltrimethylammonium hydroxide was studied in water.6 We showed that this system spontaneously forms vesicles, micelles, lamellar phases, and disk aggregates depending on the composition of the mixture.6,8-11 Moreover, in the very dilute range of concentrations (
