Oxana A. Soboleva

Colloidal properties of binary mixtures of a nonionic surfactant and monomeric or gemini cationic surfactants

The behavior of binary mixtures composed of a nonionic surfactant Triton X-100 (TX-100) and monomeric dodecyltrimethylammonium bromide (DTAB) or gemini N,N’-bis(N-dodecyl-N,N-dimethyl)-1,2-diammonium ethane dibromide (DDAB) cationic surfactants is studied upon micellization, wetting of Teflon and adsorption at the solution-air and solution-Teflon interfaces. The compositions of mixed micelles and adsorption layers, as well as the parameters of interaction between the surfactants (mixture components), were calculated using the Rubingh-Rosen model. For both mixtures, the interaction parameters are negative, and their absolute values increase in the following order: mixed micelles ≈ adsorption layers at the solution-air interface < adsorption layers at the solution-Teflon interface. The absolute values of the interaction parameters for TX-100-DDAB mixtures are larger than those for TX-100-DTAB mixtures. The adsorption of both mixtures on Teflon demonstrates synergistic effects. In case of TX-100-DDAB mixtures, the synergistic effects are also observed upon micellization, reduction of the surface tension, and wetting of Teflon.

Adsorption and Distribution of Components of Cocoamidopropyl Betaine-Lysozyme Mixtures in Water/Octane System

The scintillation phase method, interfacial tensiometry, and dynamic light scattering have been employed to study the behavior of mixtures composed of a globular protein, lysozyme, and a zwitterionic surfactant, cocoamidopropyl betaine, in a water/octane system. The comparison between the absorption values of the components, interfacial tensions, component concentrations, and aggregate sizes in the phases that are in contact, together with the analysis of the interaction between the components and the structure and surface activity of resulting aggregates, has made it possible to propose a mechanism for the behavior of the proteinzwitterionic surfactant mixture in the two-phase system.

Mixed Adsorption Layers of Nonionic and Cationic Surfactants on Quartz

Surfactant adsorption on quartz and wetting of glass by aqueous solutions of tetradecyltrimethylammonium bromide, Triton X-100, and their mixtures are studied. It is shown that synergistic adsorption of surfactants from mixed solutions occurs in the region of low concentrations. In the region of high concentrations, mixed molecular aggregates of the cationic and nonionic surfactants are formed on the surface. The structure of the mixed adsorption layers is discussed.

Effect of pluronic P123 on the distribution of nanodiamond particles in water–organic liquid systems

The effect adsorption layers of nonionic surfactant (pluronic P123) have on the distribution of nanodiamonds (NDs) between aqueous and organic phases is studied with radioactive tracers using compounds labeled with tritium. The values of reversible and irreversible adsorptions of P123 on NDs are determined. It is shown that the distribution coefficients of NDs modified by irreversibly adsorbed layers of P123 are several times higher than those of raw nanodiamonds. This result is explained by the hydrophobization of an ND’s surface, as is shown by data obtained via interfacial tensiometry and wetting.

The Distribution of Mixtures of Dodecyl Ether of Poly(23)ethylene Glycol with Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide in the Water/Octane System

The scintillation phase and tensiometry methods were used to study the mutual influence of dodecyl ether of poly(23)ethylene glycol (Brij-35) with sodium dodecyl sulfate and Brij-35 with dodecyltrimethylammonium bromide on the distribution in the water/octane system and adsorption at the liquid/liquid interface. The composition of mixed adsorption layers was determined and interaction parameters between molecules were calculated according to the Rosen model.

Selective wetting in a hydrocarbon liquid-perfluorocarbon liquid-solid system

Selective (displacement) wetting is, for the first time, investigated in a hydrocarbon liquid-perfluorocarbon liquid-fluorinated polyethylene system. Contact angles upon the selective wetting are shown to be quite sensitive to the presence of fluorocarbon groups on the surface of the polymer, and wetting inversion takes place when the surface concentration of fluorine is increased above 10−4 kg/m2.

Competitive adsorption of lysozyme and non-ionic surfactants (Brij-35 and pluronic P123) from a mixed solution at water-air and water-xylene interfaces

The adsorption of lysozyme in the presence of high molecular weight (pluronic P123) and low molecular weight (Brij-35) non-ionic surfactants was studied at liquid-liquid and liquid-air interfaces. Using tritium-labeled compounds and liquid scintillation spectrometry of tritium, we investigated the competitive adsorption of lysozyme-pluronic P123 and lysozyme-Brij-35 at the aqueous-xylene interface. The substitution of protein by both polymer and low molecular weight surfactant was observed, while the presence of lysozyme does not influence the behavior of non-ionic molecules. We found that the ionic strength of the aqueous phase does not influence the strength of the effect, while it has a significant influence on the rate of diffusion and penetration of the adsorption layer by free protein. The thermodynamics of the competitive adsorption was described by the model suggested by Fainerman and co-authors, and the obtained parameters were used to describe the interfacial tension isotherms of the respective mixtures at the aqueous-air interface. Thus, the adsorption of each component of the mixture (protein and non-ionic surfactant) at the aqueous-air interface was revealed.

The Stability of Detonation Nanodiamond Hydrosols in the Presence of Salts and Surfactants

The regions of stability and coagulation of hydrosols of oxidized detonation nanodiamonds in the presence of inorganic salts and surfactants of different types have been determined. Concentration Cc of inorganic salts corresponding to the onset of the growth of aggregates in a hydrosol dramatically decreases with an increase in coagulating ion charge z: Cc ~ z−5.3. Anionic and nonionic surfactants stabilize dispersions of nanodiamonds, while additives of cationic and zwitterionic surfactants cause coagulation. The study of the coagulating effect of alkylpyridinium chlorides has shown that the coagulation threshold halves upon elongation of the hydrocarbon chain in a surfactant molecule by a СН2 group.

Radiochemical approach in studying competitive adsorption of human serum albumin and ionic surfactants at the water/ p -xylene interface

The competitive adsorption and distribution in the bulk of the aqueous solution/p-xylene system was studied, using tritium labeling and the scintillation phase method, for human serum albumin (HSA) and ionic surfactants: dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS). Tritiumlabeled HSA, DTAB, and SDS of high specific radioactivity were obtained by the tritium thermal activation method and were purified by chromatography. Physicochemical studies were performed with HSA-SDS and HSA-DTAB mixtures at a protein concentration of 0.06 g l−1 and varied surfactant concentrations from 0.3 to 8.0 μM. The distribution ratio and the adsorption isotherm were obtained for each component of the mixture by the scintillation phase method. The effect of ultralow concentrations of surfactants on the competitive adsorption in mixtures with HSA and on the bulk distribution of the substances in the two-phase system was found. The parameters of intermolecular interaction in the adsorption layer were calculated, and a mechanism of formation of the adsorption layer was suggested.