Phase Behavior of Aqueous Mixtures of Cetyltrimethylammonium Bromide (CTAB) and Sodium Octyl Sulfate (SOS)

The phase behavior and aggregate morphology of mixtures of the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) are explored with cryotransmission electron microscopy, quasielastic light scattering, and surface tensiometry. Differences in the length...

Full description

Saved in:
Bibliographic Details
Published in:Journal of physical chemistry (1952) Vol. 100; no. 14; pp. 5874 - 5879
Main Authors: Yatcilla, Michael T, Herrington, Kathleen L, Brasher, Laura L, Kaler, Eric W, Chiruvolu, Shivkumar, Zasadzinski, Joseph A
Format: Journal Article
Language:English
Published: American Chemical Society 04-04-1996
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The phase behavior and aggregate morphology of mixtures of the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) are explored with cryotransmission electron microscopy, quasielastic light scattering, and surface tensiometry. Differences in the lengths of the two hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phases), and vesicles form spontaneously over a wide range of compositions in both CTAB-rich and SOS-rich solutions. Bilayer properties of the vesicles depend on the ratio of CTAB to SOS, with CTAB-rich bilayers stiffer than SOS-rich ones. We observe two modes of microstructural transition between micelles and vesicles. The first transition, between rodlike micelles and vesicles, is first order, and so there is macroscopic phase separation. This transition occurs in CTAB-rich solutions and in SOS-rich solutions at higher surfactant concentrations. In the second transition mode, mixtures rich in SOS at low surfactant concentrations exhibit no phase separation. Instead, small micelles abruptly transform into vesicles over a narrow range of surfactant concentration. Since the vesicles that form in mixtures of oppositely charged surfactants are equilibrium microstructures, the microstructural evolution is related solely to the phase transition and is thus under thermodynamic control. This differs from experiments reported on the dissolution of metastable vesicles, such as the detergent solubilization of biological phospholipid membranes, which may be controlled by kinetics. Despite these differences, we find that the evolution in microstructure in our mixtures of oppositely charged surfactants is analogous to that reported for biological membrane solubilization.
Bibliography:Abstract published in Advance ACS Abstracts, March 1, 1996.
ark:/67375/TPS-4Z2Q9LR8-H
istex:F25D2DA0CF5C2F9AC29E7AA4E4619D82329E55F2
ISSN:0022-3654
1541-5740
DOI:10.1021/jp952425r