Aggregation Behavior of SDS/CTAB Catanionic Surfactant Mixture in Aqueous Solution and at the Air/Water Interface

Abstract

Herein, we report the aggregation behavior of catanionic mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in solution and at the air/water interface obtained by the Langmuir-Blodgett (LB) technique. We employed Fourier transform infrared spectroscopy, in situ phase-contrast inverted microscopy, scanning electron microscopy, and atomic force microscopy to characterize the systems in solution, at the air/water interface, and in LB films. We found spherical vesicles at the SDS/CTAB ratio of 35/65 in aqueous solution and an ordered aggregated morphology called surface micelles at SDS/CTAB ratios of 35/65 to 65/35 at the air/water interface. Other mixtures (SDS/CTAB = 90/10, 10/90) were found to contain mostly disordered aggregated microstructures. An in situ time-dependent study of surface micelle formation at the air/water interface showed micelle ripening through the fusion of smaller micelles. These micelles were successfully immobilized on a glass substrate by the LB technique. Overall, the study might find application in the fundamental science of the physical chemistry of surfactant systems, as well as in the preparation of drug delivery system.

A Light-Responsive Self-Assembly Formed by a Cationic Azobenzene Derivative and SDS as a Drug Delivery System

“…Vesicles spontaneously formed in the mixtures of two single-tailed surfactants with opposite charge have been widely observed1484950515253. It is known that lipids with double hydrocarbon chains such as phospholipids have a tendency to form vesicles, i.e., liposomes.…”

“…When diluted in aqueous solutions, cationic and anionic surfactant mixtures can form a variety of microstructures, including vesicles123, rod or worm-like micelles45678 and other bilayer lamellar phases91011. Mixtures of single-tailed SDS and single-tailed dodecyl trimethyl ammonium bromide (DTAB)12, sodium octyl sulfate (SOS) and cetyl trimethyl ammonium bromide (CTAB)3131415, are two widely investigated catanionic mixtures.…”

“…Mixtures of single-tailed SDS and single-tailed dodecyl trimethyl ammonium bromide (DTAB)12, sodium octyl sulfate (SOS) and cetyl trimethyl ammonium bromide (CTAB)3131415, are two widely investigated catanionic mixtures. The aggregation behavior of cationic/anionic surfactant mixtures is mainly dependent on the ratio of cationic to anionic surfactant, the overall surfactant concentration and the nature of the surfactants, such as the chain length, and the type of polar head116. Among them, catanionic vesicles attracted particular interest because of their vesicular structure, which are similar to liposomes with the ability to encapsulate active molecules17.…”

Synthesis of Amphiphilic Azo‐Anion‐Radical Complexes of Chromium(III) and the Development of Ultrathin Redox‐Active Surfaces by the Langmuir–Schaefer Technique

“…We anticipated that when the molecules were in close proximity, inherent cohesive or repulsive forces might play a dominant role, thereby leading to a time-dependent stable state. [23] At lowpressures (ca. 10 mN m À1 ), the variation was insignificant, which indicated that the monolayer was stable.…”

Self-Healing Hydrogels Formed via Hydrophobic Interactions

“…Aqueous solutions of surfactants of opposite charges, called catanionic surfactants, exhibit unique properties originating from the strong electrostatic interactions between their oppositely charged head groups. Mixtures of the anionic surfactant SDS and the cationic surfactant CTAB form mixed micelles in both SDS-rich and CTAB-rich solutions, whereas between these compositions, vesicles and formation of a 1:1 precipitate are observed [76][77][78][79]. It was shown that the correlation length of 0.24 M CTAB-SDS increases from 0.4 to 2.5 nm as the SDS content of the surfactant mixture is increased from 0 to 15 mol%, leading to increased solubility of the hydrophobic monomer C17.3M in the micellar solution [37].…”