A small-angle neutron scattering study of surfactant aggregates formed in aqueous mixtures of sodium dodecyl sulfate and didodecyldimethylammonium bromide
2000 (English)In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 104, no 17, 4155-4163 p.Article in journal (Refereed) Published
The structure of aggregates formed in aqueous mixtures of a single-chain anionic surfactant, sodium dodecyl sulfate (SDS), and a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), has been investigated at 38 degrees C using small-angle neutron scattering (SANS). Several overall surfactant concentrations [SDS] + [DDAB] between 0.1 and 5 wt % were measured at the two SDS-rich compositions [SDS]:[DDAB] = 90:10 and 95:5. Samples with a concentration above about [SDS] + [DDAB] = 1 wt % at [SDS]:[DDAB] = 95:5 contained only somewhat elongated tablet-shaped micelles (triaxial ellipsoids) with typical values of the half-axes a (related to the thickness) = 14 Angstrom, b (related to the width) = 23 Angstrom, and c (related to the length) = 27 Angstrom. When a sample at [SDS]:[DDAB] = 95:5 is diluted below about [SDS] + [DDAB] = 1 wt %, an increasing amount of small unilamellar vesicles forms, and in the samples below about 0.2 wt %, only vesicles are observed. The average radius of the vesicles [R] increases from about 90 Angstrom at 0.3 wt % to 110 Angstrom at 0.1 wt %. The transition from micelles to vesicles with decreasing surfactant concentration was also observed in the samples at [SDS]:[DDAB] = 90:10 in which, however, an additional amount of bilayer sheets was seen to be always present. Compared with the micelles at [SDS]:[DDAB] = 95:5, the micelles formed at [SDS]:[DDAB] = 90:10 were considerably longer (c approximate to 40 Angstrom), but with similar cross section dimensions, and the vesicles formed were seen to be somewhat larger than the corresponding aggregates at 95:5. The relative standard deviation sigma(R)/[R] of the (number-weighted) vesicle size distributions was in the range 0.2 < sigma(R)/[R] < 0.3.
Place, publisher, year, edition, pages
2000. Vol. 104, no 17, 4155-4163 p.
general phase-behavior, ribbon-like micelles, sds-ddab-water, cationic surfactant, dodecyltrimethylammonium bromide, vesicle formation, mixed micelles, bile-salt, bilayer vesicles, rich side
IdentifiersURN: urn:nbn:se:kth:diva-19731ISI: 000086873000022OAI: oai:DiVA.org:kth-19731DiVA: diva2:338423
QC 201005252010-08-102010-08-10Bibliographically approved