Unusual Maximum in the Adsorption of Aqueous Surfactant Mixtures: Neutron Reflectometry of Mixtures of Zwitterionic and Ionic Surfactants at the Silica–Aqueous Interface

Abstract

The adsorption of two zwitterionic surfactants, dodecyldimethylammonium propanesulfonate (C12PS) and dodecyldimethylammonium carboxybetaine (C12CB), and of their mixtures with the cationic dodecyltrimethylammonium bromide (C12TAB) and the anionic sodium dodecylsulfate (SDS) at the silica–water interface has been studied by neutron reflection (NR). The total adsorption, the composition of the adsorbed layer, and some structural information have been obtained over a range of concentrations from below the critical micelle concentration (CMC) to about 30× the mixed CMC. The adsorption behavior has been considered in relation to the previously measured micellar equilibrium of these mixtures in their bulk solutions and their adsorption at the air–water interface. C12CB adsorbs cooperatively close to its CMC to form an almost complete bilayer on its own, whereas C12PS adsorbs more weakly in a fragmented bilayer structure. Although SDS does not normally adsorb at the silica–water interface, SDS adsorbs strongly and cooperatively with C12PS at fractional SDS compositions up to about 0.5. This cooperativity is lost when the adsorbed fraction of SDS rises above about 0.5. At this point, adsorption drops sharply, creating an unusual maximum in the variation of adsorption with a total concentration above the mixed CMC. Neither the increase in cooperativity nor the subsequent decline in adsorption results directly from variations of the independently determined monomer concentrations in the bulk solution. The adsorption maximum is predominantly the effect of strong cooperative interaction, possibly accompanied by partial segregation of SDS within the layer, followed by charge repulsion from the surface. Although the solution aggregation and adsorption at the A–W interface are similar for SDS with C12CB, the addition of SDS to C12CB at the silica–water interface promotes the opposite behavior to that of SDS with C12PS, and SDS simply disrupts the cooperative binding of C12CB. Unlike SDS, the cationic surfactant C12TAB adsorbs on silica. It therefore coadsorbs at the SiO2–W interface with either C12CB or C12PS. However, in neither case is there any pronounced cooperativity and, even though the presence of C12TAB might be expected to favor adsorption, the adsorption is generally unexpectedly low.

Aqueous, Mixed Micelles as a Means of Delivering the Hydrophobic Ionic Liquid EMIM TFSI to Graphene Oxide Surfaces

“…While a significant amount of work has been carried out to examine surfactant adsorption onto various surfaces, − little is known regarding the surface adsorption behavior of the mixed IL/surfactant systems discussed above. In this study, we aim to provide a more detailed analysis of the adsorption behavior and adsorbed layer structure of both the IL/T-20 system as well as the more commonly used IL/TX-100 system on GO surfaces.…”

Synergetic System of Zwitterionic/Anionic Surfactants with Ultralow Interfacial Tension and High Salt Resistance for Enhancing Heavy Oil Recovery

“…Previous studies have developed a series of zwitterionic molecules as the surfactants to form the high surface-active mixtures, mainly focused on their ability to reduce IFT, emulsifying characteristics for oil–water systems with the relatively low viscosity. ,,− Herein, we constructed a mixed synergistic emulsion system by introducing the zwitterionic cocoamidopropyl sulfonate betaine (CSB) and anionic sodium dodecyl benzene sulfonate (SDBS). The performance of the mixed systems on heavy oil emulsions was studied in terms of surface tension, IFT, droplet size distribution, apparent viscosity, emulsion stability, viscosity reduction, and viscoelasticity.…”

Novel Foam Stabilized by Fatty Amine Polyether Carboxylate and AOS Binary Blend for Enhanced Oil Recovery

“…Since betaine is a zwitterionic surfactant, its positive charge in the molecule is electrostatically attracted to the negative charge of the anionic surfactant, which increases surface excess and potentially improves film stability of the foam . However, high adsorption occurred for betaine because of the electrostatic attraction between the positively charged quaternary ammonium groups in betaine and the negatively charged sandstone, − which is about 10 times higher than that of an anionic surfactant on sandstone. , By blending anionic surfactants with betaine surfactants, anionic surfactant adsorption is expected to be influenced. Mannhardt et al have observed that the adsorption of the anionic/betaine blend is comparable to that of betaine surfactant itself.…”

“…Mannhardt et al 13 have observed that the adsorption of the anionic/betaine blend is comparable to that of betaine surfactant itself. Ma et al 15 have observed that although anionic sodium dodecyl sulfate (SDS) does not normally adsorb at the silica−water interface, SDS adsorbs strongly and cooperatively with betaine surfactants (dodecyldimethylammonium propanesulfonate) at a fractional of SDS up to about 0.5.…”