Influence of nanoparticle addition to Winsor surfactant microemulsion systems

The influence of adding negatively charged silica nanoparticles to multiphase Winsor microemulsion systems of cationic surfactant/alcohol cosurfactant is reported. It is found that the particles do not change the salt-induced progression of Winsor systems to any great extent, even when added at the same concentration as the surfactant. We find that all of the particles transfer from water where they originate to oil at all salt concentrations, although the distribution of surfactant between phases is unaffected. It is ascertained that alcohol addition renders particles more hydrophobic promoting this transfer. Emulsions prepared from the equilibrium microemulsion and excess phase(s) invert from oil-in-water to water-in-oil with increasing salt concentration, such that the continuous phase is the one containing the surfactant aggregates. Their stability to coalescence is extremely low, due to mainly the ultralow tensions at the oil-water interface. Particle addition does not alter the emulsion stability, implying that they are not adsorbed to drop interfaces. © 2010 Elsevier B.V

Effects of Mixtures of Alkanes on the Bending Rigidity Constant K of AOT Monolayers at the Planar Oil-Water Interface

We have studied the phase diagrams of brine/oil/AOT mixtures in which the oils are mixtures of octane and tetradecane and the amount of AOT is small. In addition, the properties of the AOT monolayer at the brine/oil interface as a function of the volume fraction $\phi$ of tetradecane in the oil have been measured. The values of the interfacial tension and the phase diagram behaviour show that the Equivalent Alkane Carbon Number concept is valid in these systems, where a small change of $\phi$ induces a large change in the phase diagram. In addition we show that this concept applies to the bending elastic modulus $K$ and probably to the saddle splay modulus $\bar{K}$

Food-grade pickering stabilisation of foams by in situ hydrophobisation of calcium carbonate particles

The aim of this study was to investigate the possibility of stabilising foam bubbles in water by adsorption of calcium carbonate (CaCO3) particles. Because CaCO3 is hydrophilic and not surface-active, particles were hydrophobised in situ with several emulsifiers. The used emulsifiers were food-grade and negatively charged at the pH employed. The effect of particle addition on foamability and foam stability of solutions containing either β-lactoglobulin, sodium caseinate, Quillaja, sodium dodecanoate (SD) or sodium stearoyl-2-lactylate (SSL) was studied. It was found that the ability of the emulsifiers to induce surface activity such that the particles are able to adsorb to the air-water interface is related to their structure. The structure needs to consist of a well-defined hydrophobic part and a charged part. Large emulsifiers with a complex structure, such as β-lactoglobulin, sodium caseinate and Quillaja, were able to partially hydrophobise the particles but were not able to act synergistically with the particles to increase the foam stability. Low molecular weight emulsifiers, however, consisting of a single tail with one charged group, such as SD and SSL, adsorbed at the particle surface rendering the particles partially hydrophobic such that they adsorb to the air-water interface. In a subsequent investigation, the pH was changed to a value typical for food products (pH 6–7) and the addition of milk salts on the foamability and foam stability was assessed. Based on these results, the use of food-grade CaCO3 particles hydrophobised in situ with food-grade surfactants (SD or SSL) to prepare ultra-stable aqueous foams is demonstrated

Non-aqueous foams in lubricating oil systems

We have investigated the foaming properties of mixtures of a hydrocarbon oil solvent with various low molar mass, polymeric and overbased detergent particle additives used in lubricating oils. Foam formation occurs only when the additive concentration and temperature are such that the single-phase mixtures are close to a phase separation boundary when solvent affinity for the solute is low. This is likely to maximise the tendency of the solute to adsorb at the liquid-air surface and thereby promote foam formation. Multi-phase mixtures either maintain or suppress the foamability of the single-phase mixtures. The foams formed contain spherical, polydisperse gas bubbles and liquid volume fractions greater than about 20 vol.% indicating they are " wet" , transient foams in which the adsorbed solute films at the liquid-air surface can affect liquid drainage but are incapable of resisting coalescence between contacting bubbles. Consistent with this model, the foam half-life is found to scale with the kinematic viscosity of the liquid. © 2010 Elsevier B.V

Fluctuation effects on wetting films

International audienc