The effect of high volume fractions of latex particles on foaming and antifoam action in surfactant solutions

Insight on Methane Foam Stability and Texture via Adsorption of Surfactants on Oppositely Charged Nanoparticles

We report the phase behavior of a dispersion of alumina-coated silica nanoparticles in the presence of an anionic surfactant (sodium fatty alcohol polyoxyethylene ether sulfate), and then describe the influence of surfactant/nanoparticle concentration ratio on the stability of methane foam as a potential fluid for enhanced oil recovery application. The surface tension of the methane/aqueous phase interface, surface charge, and size of the particle aggregates and amount of surfactant adsorption were characterized as a function of surfactant/nanoparticle ratio. Five adsorption stages, which are described in terms of the extent and type of the surfactant coverage on the nanoparticle surface, explain the behavior of the solution at different surfactant/nanoparticle ratios. The static foam generation experiments were conducted to monitor the variation of the foam stability and texture over the defined adsorption stages. The surface tension trends illustrate that the affinity of nanoparticles for the gas-liquid interface is strongly affected by the adsorption extent of AES molecules on the particle surface. At high surfactant/nanoparticle ratio, the adsorbed surfactant bilayer causes a high hydrophilicity of the particles that significantly pushed the particles away from the gas-liquid interface. At the most hydrophobic state of the particles which occurred at the ratio of 0.2, the foam structure collapsed quickly. The most stable foam with fine texture was found at surfactant/nanoparticle ratio less than 0.008 at which the particles are partially covered with surfactants and have smaller aggregate size. The findings provide a better understanding of the interaction between oppositely charged nanoparticle/surfactant pairs and how that interaction affects foam stability. It is demonstrated that substitution of absolute concentration by surfactant/nanoparticle ratio can truly govern the foam stability and texture. The results can be beneficial to predict the foam behavior in its numerous applications and whether interactions will be synergistic, antagonistic, or neutral.

CO2 foam properties and the stabilizing mechanism of sodium bis(2-ethylhexyl)sulfosuccinate and hydrophobic nanoparticle mixtures

In this work, we have prepared CO2-in-water foam by mixing partially hydrophobic SiO2 nanoparticles and sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and studied its properties. The observation of the appearance of the foam revealed that, with the continuous addition of AOT, the phase behavior of the SiO2 nanoparticle and the AOT mixed system transformed from that of a two-phase system of aggregated nanoparticles into that of a uniform dispersed phase. Both foaming ability and foam stability were optimized when the nanoparticles and the AOT were mixed in a proportion of 1 : 5. On the basis of our findings from measurements of the dispersion properties, including measurements of the adsorption isotherm of the surfactant on the nanoparticles, zeta potentials, interfacial tension and the three-phase contact angle, we concluded that the synergistic interactions between the SiO2 nanoparticles and the AOT led to the adsorption of nanoparticles around the bubble surface and the formation of a spatial network structure of nanoparticles in the film, thereby enhancing the mechanical strength of the bubble and improving the resistance to outside disturbances, deformation and drainage. Laser scanning confocal microscopy (LCSM) analysis of the same foams further confirmed the existence of a "viscoelastic shell" wrapped around and protecting the bubble.

Properties of multi-phase foam and its flow behavior in porous media

Aqueous foams were produced with partially hydrophobic SiO₂ nanoparticles and sodium dodecyl sulfate (SDS) dispersions.

Mechanistic understanding of the modes of action of foam control agents

In this paper we present briefly our current understanding of the modes of action of foam control agents (often termed "defoamers" or "antifoams"). After summarizing the background knowledge, reviewed in previous articles, the focus of the presentation is shifted to the antifoam studies from the last decade. The new experimental results, obtained by various research groups, are reviewed briefly to reveal the main mechanisms of antifoam action and the related key factors, governing the efficiency of the foam control agents. The role of the entry, spreading and bridging coefficients, of the entry barrier of the antifoam entities, and of the dynamics of surfactant adsorption is specifically discussed.

Thinning of a vertical free-draining aqueous film incorporating colloidal particles

The drainage under gravity of a vertical foam film formed on a wire frame has been investigated. Dual-wavelength optical interferometry was used so that unambiguous fringe order assignments could be made, enabling absolute film thicknesses to be calculated with confidence. Films were stabilized by nonionic polypropylene glycol surfactant. Half-micrometer silica particles with varying degrees of hydrophobicity were added to the film-forming liquid to investigate their effect on film drainage rate and stability. Hydrophilic particles had little or no effect, while hydrophobic particles slowed the drainage of the film and caused a minor increase in film lifetime, from approximately 10 to approximately 30 s. In both the hydrophilic and hydrophobic cases the films ruptured when they reached a thickness of approximately 2 particle diameters. Particles of intermediate hydrophobicity had the most significant effect, increasing film lifetime by an order of magnitude over that for hydrophilic particles. The intermediate particles allowed films to thin down to a thickness less than the particle diameter, indicating that particles bridge across the entire film. This did not occur with more hydrophobic particles even though they were embedded in each of the two film surfaces. These results correlate well with previous literature on particle-laden foams. The film thickness and drainage measurements allow drainage mechanisms for the different particles to be identified, thus providing a mechanistic explanation for the observation by several previous authors that foams formed in the presence of particles, for example during mineral processing, have the greatest stability when the particles are of intermediate hydrophobicity.

Foam drainage in the presence of nanoparticle-surfactant mixtures

The drainage of SiO(2) nanoparticle-cationic surfactant (TTAB) mixtures through calibrated aqueous foams had been studied by combining several approaches on both the macroscopic and the local scale. Macroscopic measurements reveal a strong stabilizing effect arising for nanoparticle concentrations as low as 2 wt % mainly because of a drainage kinetic slow-down dependent on the nanoparticle concentration. We show that the variation of the viscous parameters (bulk viscosity, interfacial viscosity, or both) in the classical theoretical models of foam drainage, mainly developed for aqueous surfactant solutions, does not enable fitting experimental data obtained via steady- or free-drainage strategies for [SiO(2)] > or = 2 wt %. In contrast, the quantitative analysis of the data obtained from front propagation velocities has revealed a drainage regime transition from a node-dominated regime toward a Plateau-border-dominated regime upon nanoparticle concentration increase. Observations performed at the Plateau border scale brought to light the drainage kinetic slow-down process by evidencing that the presence of insoluble aggregates induces traffic jamming and even cork formation for silica concentrations above 2 wt %. Considering these observations, a simple mechanism of aggregate growth and cork formation is proposed. Finally, we analyze the discrepancy between experiments (steady- and free-drainage methods) and theory by pointing out that the hypothesis relative to the foam structure that is usually assumed for both the liquid fraction calculation and the determination via conductivity measurements is strongly modified when large insoluble aggregates are present in the system. In this view, the method based on the liquid fraction determination through the measurement of the front propagation velocity seems to be the most suitable for studying the drainage of colloidal dispersion because of the lower dependence of this approach toward hypothesis on the local geometry of the foam continuous phase.