Vesicle formation and general phase behavior in the catanionic mixture SDS-DDAB-water. The cationic-rich side

• Type: Article in International Scientific Journal
• Date: 1999

Authors

Marques, EF (Author) FCUP; Regev, O (Author) Other; Khan, A (Author) Other; Miguel, MD (Author) Other; Lindman, B (Author) Other

Journal

Title: Journal of Physical Chemistry B

Vol. 103

Pages: 8353-8363

ISSN: 1520-6106

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 158 Citations

Scopus - 160 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-001-39K

DOI: 10.1021/jp990852p

Abstract (EN): The phase behavior in the cationic-rich side of the phase diagram of the mixed system sodium dodecyl sulfate (SDS)-didodecyldimethylammonium bromide (DDAB)-water at 25 degrees C is presented. DDAB is a double-chained surfactant and thus it tends to self-assemble in water into bilayer structures-vesicles and lamellar phases. The phase diagram of the binary system DDAB-water has been studied, and some features of the diluted region as revealed by surfactant NMR self-diffusion and light microscopy are shown. The structural and phase behavior effects resulting from the addition of SDS are then investigated by complementary microscopy and NMR methods. Upon adding SDS to DDAB dispersions, the area for which a single phase of vesicles occurs is largely extended and a lobe is defined in the phase diagram. The DDAB-rich vesicles are essentially unilamellar and characterized by large sizes (range 0.1-5 mu m) and high polydispersity, as probed by combined cryo-TEM and light microscopy. Self-diffusion measurements show a nonmonotonic variation of water self-diffusion coefficients with the molar fraction of SDS in the mixture, which is correlated to a nonmonotonic variation of mean vesicle size. Microscopy results support this picture. The trends are qualitatively reproduced if initially sonicated (nonequilibrium) DDAB vesicles are used to prepare the catanionic mixtures. The observations are rationalized in terms of an interplay between two opposing effects associated with the presence of SDS in the bilayer-electrostatic effects and packing effects.

Language: English

Type (Professor's evaluation): Scientific