Surfactant layers at the air/water interface: structure and composition.

Polymer/surfactant interactions at the air/water interface

Solutions of surfactant–polymer mixtures often exhibit different foaming properties, compared to the solutions of the individual components, due to the strong tendency for formation of polymer–surfactant complexes in the bulk and on the surface of the mixed solutions. A generally shared view in the literature is that electrostatic interactions govern the formation of these complexes, for example between anionic surfactants and cationic polymers. In this study we combine foam tests with model experiments to evaluate and explain the effect of several polymer–surfactant mixtures on the foaminess and foam stability of the respective solutions. Anionic, cationic, and nonionic surfactants (SDS, C12TAB, and C12EO23) were studied to clarify the role of surfactant charge. Highly hydrophilic cationic and nonionic polymers (polyvinylamine and polyvinylformamide, respectivey) were chosen to eliminate the (more trivial) effect of direct hydrophobic interactions between the surfactant tails and the hydrophobic regions ...

Foaming and foam stability for mixed polymer-surfactant solutions: effects of surfactant type and polymer charge.

Complex Fluids of Poly(oxyethylene) Monoalkyl Ether Nonionic Surfactants

Interaction between polymer and surfactant bearing opposite charges is much more complex from a physicochemical point of view as compared to interaction between ionic surfactant and nonionic polymer. Electrostatic and hydrophobic interactions interplay in the former, whereas the hydrophobic effect is the prevailing factor in the latter. We have studied the interaction between a water-soluble polyanion, sodium salt of carboxymethylcellulose (NaCMC), with a cationic amphiphile, CTAB, in aqueous medium. There were manifold discrepancies with the reported works in NaCMC-alkyltrimethylammonium bromide, which is assumed to be an effect of difference in degree of substitution, which in turn affects the charge density of the polymer chain. We have noticed that the bulk complexation and interfacial interaction driven by electrostatic forces operate side by side. Thereafter, there is a wrapping process by the polyanion to the polymer-induced smaller surfactant aggregates driven by increase in entropy of the solution as a result of expulsion of the counterions from the ionic atmosphere around the surfactant aggregate. Because of the electrostatic interaction, hydrophobicity of the polymer-surfactant complex increases, leading to coacervation, and again solubilization in the hydrophobic core of the self-aggregated structure provided by the added excess CTAB. The tensiometric, conductometric, microcalorimetric, and turbidimetric techniques have been applied to address these problems.

Sodium carboxymethylcellulose-CTAB interaction: a detailed thermodynamic study of polymer-surfactant interaction with opposite charges.

Specular neutron reflection and surface tension have been used to investigate the composition and structure of the surfactant−polymer mixture of sodium dodecyl sulfate, SDS, and the cationic polymer poly(dimethyldiallylammonium chloride) at the air−water interface. The variation of surface tension with SDS concentration shows a complex behavior, with a marked increase between the concentrations normally associated with the critical aggregation concentration and the critical micellar concentration. The neutron reflectivity measurements show that this change in surface tension is associated with changes in the amount of SDS and polymer at the interface. The changes are attributed to the competition between the formation of surface and solution surfactant−polymer complexes.

Organization of Polymer−Surfactant Mixtures at the Air−Water Interface: Sodium Dodecyl Sulfate and Poly(dimethyldiallylammonium chloride)

Small-angle neutron scattering has been used to study the structure and composition of mixed ionic−nonionic surfactant micelles. A comparison between two different mixed surfactant systems, sodium dodecyl sulfate (SDS) and hexaethylene glycol monododecyl ether (C12EO6) and hexadecyltrimethylammonium bromide (C16TAB) and C12EO6, both in 0.1 M NaCl, has been made. In the latter system, ideal mixing is observed, and in the former, departure from ideality, broadly consistent with regular solution theory, RST, is observed. The deviations from the predictions of RST are attributed to subtle changes in the packing of the two surfactants in the mixed micelles. For the SDS/C12EO6 mixture, the micellar aggregation number is essentially constant with composition and concentration, whereas for the C16TAB/C12EO6 mixture there is a marked micellar growth with increasing concentration and mole fraction of C12EO6 in solution. The SANS results on structure and composition are compared with the results reported for other m...

Structure and Composition of Mixed Surfactant Micelles of Sodium Dodecyl Sulfate and Hexaethylene Glycol Monododecyl Ether and of Hexadecyltrimethylammonium Bromide and Hexaethylene Glycol Monododecyl Ether

Specular neutron reflection and small-angle neutron scattering have been used to evaluate the solution and interfacial properties of the anionic surfactant, sodium dodecyl sulfate, SDS, and of the mixed anionic–non-ionic surfactants of SDS and hexaethylene glycol monododecyl ether, C12E6, in the presence of cationic polymers (dimethyldialylammonium chloride–acrylamide copolymers). The data have been interpreted using a simple model of surfactant association to polymers and regular solution theory has been applied to include the mixed-surfactant systems.

N. Warren

Papers

Organization of Polymer−Surfactant Mixtures at the Air−Water Interface: Sodium Dodecyl Sulfate and Poly(dimethyldiallylammonium chloride)

Structure and Composition of Mixed Surfactant Micelles of Sodium Dodecyl Sulfate and Hexaethylene Glycol Monododecyl Ether and of Hexadecyltrimethylammonium Bromide and Hexaethylene Glycol Monododecyl Ether

Composition of mixed surfactant–charged polymer complexes adsorbed at the air/water interface