B. D. Summ

Wetting of Solids by Aqueous Solutions of Surfactant Binary Mixtures: 1. Wetting of Low-Energy Surfaces

Wetting of glass by aqueous solutions of binary mixtures of cationic and nonionic surfactants was studied in the range of overall concentrations c0 = 10–8–10–2 M at the molar fraction of cationic surfactant α = 0.2, 0.5, and 0.8. It was established that the character of glass wetting is determined by the presence of cationic surfactant in the mixture: contact angle isotherms θ(c0) exhibit maximum, as in the case of individual cationic component solutions. Maximal θ values are virtually independent of the nature of cationic surfactant and its molar fraction in the mixture. It was shown that the synergistic effect in glass wetting is controlled by the chemical structure of surfactant cation.

Synthesis of Barium Sulfate Nanoparticles in Water-in-Oil Microemulsion Systems

Micellar solutions of poly(ethylene glycol) octylphenyl ether and n-hexyl alcohol in cyclohexane were used to study the formation of water-in-oil microemulsion system and to synthesize barium sulfate nanoparticles. Barium sulfate particles (the average diameter is 10 nm) were obtained by mixing two microemulsion systems containing Ba2+and SO2–4ions. It was shown that the sizes of BaSO4particles measured by the dynamic light scattering and electron microscopy are in good agreement with each other.

The Kinetics of Dewetting of Hydrophobic Surfaces during the Evaporation of Surfactant Solution Drops

The kinetics of dewetting (a decrease in contact angles and wetted surface area) during the evaporation of drops of cetyltrimethylammonium bromide (CTAB) solutions from paraffin and Teflon surfaces was studied in a wide concentration range. Three different stages of this process were found: (1) a monotonic decrease in the contact angle at a “fixed” position of the three-phase contact line, (2) contraction of the wetted surface area (the drop base) at a constant contact angle, and (3) simultaneous contraction of the drop base and a decrease in the contact angle. The CTAB distribution over a solid surface after the drop evaporation was studied by autoradiography. Depending on the surfactant concentration and the nature of a hydrophobic substrate, dewetting occurs by two mechanisms: slipping and “carpet rolling.”

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.

Wetting effect of aqueous binary mixed solutions of cationic and nonionic surfactants

Wetting of low-energy solid surfaces (polymers, hydrophobized glass) with aqueous solutions of binary mixtures of cationic and nonionic surfactants was investigated at molar fractions of the cationic surfactant of 0.2, 0.5, and 0.8. In a narrow concentration range, the non-additive effect of wetting was observed: wetting of the solid surfaces with solutions of the mixtures is better than that would be expected from the additive behavior of the components. The magnitude of the effect depends on the surface energy of the solid substrate, total surfactant concentration in a mixture, and molar fraction of the cationic component. The wetting effect of surfactant mixtures with respect to low-energy solid surfaces can be predicted using the surface tension isotherms.

Intermolecular interactions in the binary systems of cationic and nonionic surfactants

The micellization of the mixtures of cationic (cetyltrimethylammonium bromide, cetylpyridinium bromide) and nonionic (Triton X-100) surfactants at various content of components in aqueous solutions, as well as the adsorption of surfactants at the air/solution interface were studied. The effect of negative deviation from the ideality was discovered during the formation of mixed micelles and adsorption layers. Various theoretical approaches to the quantitative description of mixed systems were compared within the framework of the model of pseudophase separation. The parameters of intermolecular interaction in mixed micelles and adsorption layers, excess free energies of micellization and adsorption, compositions of micelles and adsorption layers were calculated. It was shown that the use of various theoretical approaches for the analysis of interactions in surfactant mixtures leads to close numerical results. It was shown that the composition of mixed micelles and adsorption layers, as well as the parameters of intermolecular interaction and the excess free energy depend on the relative content and molecular structure of surfactants (mixture components).

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.

Adsorption and Micellization in Solutions of Dodecylpyridinium Bromide–Nonionic Surfactant Mixtures

Dependences of the surface tension of aqueous solutions of cationic (dodecylpyridinium bromide) and nonionic (Tween 80, Triton X-100) surfactants and their mixtures on total surfactant concentration and solution composition were studied. The values of critical micellization concentration (CMC) and excess free energy of adsorption were determined from tensiometric measurements. Based on Rubingh–Rosen model (approximation of the theory of regular solutions), the compositions of micelles and adsorption layers at the solution–air interface as well as parameters of interaction between the molecules of cationic and nonionic surfactants were calculated for the systems indicated above. It was established that, in the case of surfactant mixtures with considerable difference in the CMCs, the micelles of individual surfactant with lower CMC value are formed. The effect of negative deviation from the ideality during the adsorption of surfactants from mixed solutions at the solution–air interface was disclosed. It was shown that the interaction energy depends significantly on the composition of mixed systems.

Autoradiography studies of the processes of wetting and spreading

Data of the studies of wetting and spreading in liquid metal-solid metal systems, as well as the modification of various solid surfaces with aqueous surfactant solutions, by the autoradiography technique are reported.

Reverse Flow of Mixed Surfactant Solutions after Their Capillary Rise

The reverse flow (i.e., the efflux from glass capillaries occurring after the stop of capillary rise) of mixed aqueous solutions of nonionic (Triton X-100) and cationic (cetyl- and dodecyltrimethylammonium bromides) surfactants is studied. The effect of electrolytes (salts and acids) on the process kinetics and the wetting in these systems is investigated. Possible causes of the reverse flow are discussed. They are related to the peculiar features of the interaction of nonionic and cationic surfactants with glass and to the differences in the surfactant adsorption from quiescent and moving solutions. It is shown that the wetting by the mixed surfactant solutions, including its kinetics, can be controlled by the addition of electrolytes.