Foam Films Research Articles

Formation and stabilization of CO2 bubbles with different sizes and the interaction with solid particles

Various applications of CO2 have received extensive attention, especially those realizing the reuse of the greenhouse gas and meeting the application requirements simultaneously, of which the CO2 enhanced oil recovery (EOR) and enhanced gas recovery (EGR) approaches is a paradigm. In recent years, the applications of CO2 foam as flooding or fracturing system are both of the research hotspots. Since conventional surfactants are generally poor in stabilizing CO2 foam, the exploration of CO2 foam stabilizer is of great significance, while it is also a difficult problem. In this work, a kind of hydrophobically modified water-soluble polyelectrolyte (HMPE) was used in the stabilization of CO2 foam containing millimeter-sized and micron-sized bubbles, which both exhibit high stability and perfect foam viscoelasticity, due to the enhancement of the mechanical strength of the foam films through HMPE absorbed at the gas/liquid interfaces. The interaction between the CO2 bubbles and ceramiste particles was investigated, the mechanism of the excellent sand-carrying performance of the CO2 foam system was discussed. Based on the comprehensive understanding of all aspects of the properties, the HMPE-CO2 foam system has bright potential being used in the CO2-foam fracturing.

Compact and low-frequency broadband microwave metamaterial absorber based on meander wire structure loaded resistors

In this paper, a compact and low-frequency broadband microwave metamaterial absorber (MMA) based on meander wire structure loaded with lumped resistor has been proposed and investigated numerically and experimentally. Compared with the single meander wire structure, the bandwidth and absorption level of the proposed MMA loaded with lumped resistors can be improved extremely. The retrieved equivalent constitutive parameters and simulated electric and magnetic fields distributions have been demonstrated to illustrate the mechanism underlying observed absorption. The simulated results exhibit that the proposed MMA can keep a good stability in a wide angular range for both transverse electric (TE) and transverse magnetic (TM) waves under normal and oblique incidence. Further simulated results indicate that the performance of the MMA can be adjusted by changing parameters of unit-cell structure and lumped resistors. Finally, we have fabricated a modified MMA sample practically, composing of meander wire structure loaded with lumped resistors, FR-4(loss), foam and continuous metal film. The modified MMA yields absorbance of over 85% from 1.84 GHz to 5.96 GHz in the experiment, and the relative bandwidth is about 105.6%, which is agreement reasonable with simulation.

Bubble entrainment by a sphere falling through a horizontal soap foam

Processes such as particle separation, froth flotation and explosion suppression rely on the extent to which particles are trapped by foam films. We simulate the quasi-static motion of a spherical particle through a stable, horizontal soap film. The soap film subtends a fixed contact angle, in the range , where it meets the particle. The tension and pressure forces acting on the particle are calculated in two cases: when the film is held within a vertical cylinder, trapping a bubble but otherwise free to move vertically, and when the outer rim of the film is held in a fixed circular wire frame. Film deformation is greater in the second case, and the duration of the interaction therefore increases, increasing the contact time between particle and film. As the soap film returns towards its equilibrium shape following the passage of the particle a small bubble is trapped for contact angles below a threshold value of 90°. We quantify how the size of this bubble increases when the particle is larger and when the contact angle is smaller.

Enhanced foam-stabilizing performance by the addition of clays: A comparison of magnesium aluminum silicate with sodium bentonite

High-temperature-resistant foam stabilizers are desperately required for high-temperature conditions, such as in geothermal wells. In this study, nano‑magnesium aluminum silicate (NMAS) and micro‑magnesium aluminum silicate (MMAS) particles have been studied and compared with sodium bentonite (Na-Bent) as high-temperature-resistant foam stabilizers. It is found that increasing the temperature could facilitate aggregation of clay dispersion, and the increase of particle size results in significant positive effect on apparent viscosity, interface dilational modulus, foam film thickness, and eventually drainage half-life (T0.5) of the foam. Simultaneously, it leads to a negative impact on the initial foam volume (V0) and foam diameter. Moreover, NMAS even possesses excellent foam stabilization effect after being aged at 320 °C for 16 h that it could still dramatically extend T0.5 to 9.78 h, compared to 45.52 and 13.78 min for MMAS and Na-Bent, respectively. Furthermore, V0 of Na-Bent-stabilized foam cannot resist the influence of NaCl and CaCl2 even when only 1.0 wt% NaCl or 0.1 wt% CaCl2 is added. By comparison, V0 of NMAS- and MMAS-stabilized foam drilling fluids are comparatively insensitive to NaCl and CaCl2 until the concentration of 3.0 wt% and 0.2 wt%, respectively. Not only has this study provided a guideline for using clay minerals as foam stabilizers under various high-temperature conditions, but we have also discovered an outstanding high-temperature-resistant foam stabilizer, NMAS, which produces an excellent foam-stabilizing performance even at temperatures as high as 320 °C.

Dynamic Stabilization of Foam Films with Acoustic Sound.

This paper demonstrates the stabilization of single foam films at dynamic conditions induced by exposure to the acoustic sound. The foam films were formed from aqueous solutions using a Sheludko cell. In the presence of sound at certain sound frequencies and above certain thresholds of sound amplitude, the lifetime of the film with 1 × 10-4 M sodium dodecyl sulfate (SDS) in the presence of 0.1 M NaCl was significantly increased, and a stabilization map was drawn to show the three levels of film stability (i.e., unstable, metastable, and stable) obtained over a broad range of sound frequencies (1-19 kHz) and amplitudes (74-125 dB). In particular, stable films were observed at relatively high frequencies (14-19 kHz) and high amplitudes (>107 dB) and metastable films were observed at intermediate frequencies (8.8-9.3 kHz) and high amplitudes (>111 dB). The stabilization effect was also demonstrated with different surfactants at different concentrations, at different electrolyte concentrations (in the presence and absence of the surfactant), and at different temperatures. Image analysis suggested the presence of liquid flow within the films that were stabilized by exposure to the acoustic sound. The stabilization effect could be attributed to the hydrodynamic pressure arising at dynamic conditions.

Stabilization of foam using hydrophobic SiO2 nanoparticles and mixed anionic surfactant systems in the presence of oil

The use of nanoparticles has been intensively investigated to improve foam flooding in oil production. Because nanoparticles have larger adhesion energy at the air-water interface than the surfactant, they help to prevent a gas diffusion between bubbles that leads to foam film rupture. In this study, the detail investigation on the behavior of mixed-surfactant foam stabilized by silica nanoparticles (SiO2-NPs) was conducted. The binary surfactant systems of an internal olefin sulfonate (IOS) and sodium polyethylene glycol monohexadecyl ether sulfate (C32H66Na2O5S) were selected. The impact of alkane oil with varying carbon chain length (i.e. hexane, octane, dodecane, and hexadecane) was investigated. The findings from a similar system of foam in deionized water (DI) and brine solution also presented for comparison. For SiO2-NPs foam/brine system in the presence of oil, the foam stability increased to a maximum with respect to certainly added nanoparticles (10 ppm), and the additional surfactant is required to maintain the foam stability when the alkane chain length increases. The foam stability parameter indicated by spreading (S) and entering (E) coefficients shows that the SiO2-NPs foam systems with the shorter-tail surfactant (mixed C15-18 IOS) had lower the coefficient values compared to the longer-tail one (mixed C19-23 IOS), suggesting that the structure of surfactant influents on foam stability. The findings from this study bring an understanding of the SiO2-NPs foam/alkane oil behavior in the brine solution, which helps to select the appropriate system for improving foam flooding in EOR applications.

Ethanol enhanced anionic surfactant solubility in CO2 and CO2 foam stability: MD simulation and experimental investigations

CO2 foam has been widely scrutinized as a potential candidate in enhanced oil recovery while reducing CO2 emissions through geo-sequestration due to the high-efficiency CO2 mobility control ability. However, its application has been retarded partially because of the limited solubility of commercial and environmentally friendly surfactants in supercritical CO2. In this work, the challenge of limited solubility of surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in CO2 is overcome by using ethanol as a co-solvent. The presented MD simulation reveals the underlying mechanism of the ethanol increased solubility of AOT in CO2 and the subsequently water-CO2 interfacial properties favorable for a stable CO2 foam. Experimental observation is in good accordance with the MD simulation that foamability and foam stability both significantly increase with ethanol as co-solvent, and their dependence on ethanol content. With ethanol as co-solvent to assist the dissolution of AOT in CO2, the CO2 foam has a high stiffness and the foam film has a high dilational modulus under high pressure of 15 MPa, which explain the stable CO2 foam. Experiments also show that ethanol helps the foam regeneration, making the practical oil field application of the presented system even more promising.

Formation of stable aqueous foams on the ethanol layer: Synergistic stabilization of fluorosurfactant and polymers

The extreme instability of aqueous foams on the ethanol layer is an important issue to consider in the application of fire-fighting foams. We attempt making stable aqueous foams on the ethanol layer by using sodium dodecyl sulfate (SDS) as the foamer, with fluorosurfactant (FC1157) and xanthan gum polymers (XG) as the stabilizing agents. The surface properties, foam stability, and fire extinguishing performance of our studied systems were investigated respectively. The results show that ethanol destroys aqueous foams by dehydration and polar ethanol has a more significant defoaming effect than non-polar heptane. XG and FC1157 can inhibit the adverse effects of ethanol on foam stability. The addition of FC1157 improves the stability of the foam films and slows down the ethanol-induced dissolution of foams. XG polymers tend to form a gel-like membrane at the foam/ethanol interface, minimizing the mass transfer between foam and ethanol. The lifetime of foam stabilized by FC1157/ XG is much longer than that of foam stabilized by FC1157 or XG alone in the presence of ethanol. Foams can go from unstable foams to foams being stabilized by both XG membrane and FC1157 synergistically. As a result, the synergism of FC1157 and XG in stabilizing foams significantly enhances the fire extinguishing performance of foam.

Effect of surfactant redistribution on the flow and stability of foam films.

The viscous froth model for two-dimensional (2D) dissipative foam rheology is combined with Marangoni-driven surfactant redistribution on a foam film. The model is used to study the flow of a 2D foam system consisting of one bubble partially filling a constricted channel and a single spanning film connecting it to the opposite channel wall. Gradients of surface tension arising from film deformation induce tangential flow that redistributes surfactant along the film. This redistribution, and the consequent changes in film tension, inhibit the structure from undergoing a foam-destroying topological change in which the spanning film leaves the bubble behind; foam stability is thereby increased. The system's behaviour is categorized by a Gibbs-Marangoni parameter, representing the ratio between the rate of motion in tangential and normal directions. Larger values of the Gibbs-Marangoni parameter induce greater variation in surface tension, increase the rate of surfactant redistribution and reduce the likelihood of topological changes. An intermediate regime is, however, identified in which the Gibbs-Marangoni parameter is large enough to create a significant gradient of surface tension but is not great enough to smooth out the flow-induced redistribution of surfactant entirely, resulting in non-monotonic variation in the bubble height, and hence in foam stability.

Properties of the micelles of sulfonated methyl esters determined from the stepwise thinning of foam films and by rheological measurements

Properties of the micelles of sulfonated methyl esters determined from the stepwise thinning of foam films and by rheological measurements

Effect of initial adsorption coverage and dynamic adsorption layer formation at bubble surface in stability of single foam films

The paper presents the experimental studies on influence of degree of initial adsorption coverage and structure of the dynamic adsorption layer over a rising bubble on stability of single foam films formed at surfaces of solutions of surface-active-substances namely n-octanol, n-hexadecyltrimethylammonium bromide (CTAB) and polyoxyethylenesorbitan monooleate (Tween80). Stability of single foam films formed by the colliding bubble under different experimental conditions were determined on the basis of systematic measurements of a single bubble lifetime in self-elaborated set-up. The experiments were supplemented by theoretical calculations of values of rupture thicknesses of the foam films, determined according to the Radove-Dimitrov-Ivanov model of drainage, which allows to consider formation of symmetrical and unsymmetrical foam films, depending on estimated structure of the dynamic adsorption layer. It was found that film lifetime depends strongly on the structure (stage of development) of motion-induced dynamic adsorption layer over the rising bubble surface. Moreover, it was shown that the bubble with completely different degree of initial adsorption coverage can form foam film of similar stability. This effect was attributed to the fact that eventual degree of the bubble adsorption coverage can reach comparable (and in some cases even equilibrium) value before film formation with identical structure of the DAL and degree of liquid/gas interface immobilization.

Production and characterization of fully biobased foamed films based on gelatin

The objective of this study was to produce and characterize gelatin foamed films using extrusion. Three “optimum” formulations containing tannic acid, nanoclays (Cloisite Na+), glycerol, water, and gelatin, as well as three “controls” without tannic acid and nanoclays were prepared by calendering. Furthermore, the three “optimum” formulations were produced by extrusion film blowing only, since no stable processing conditions could be obtained for the controls. A complete set of sample characterization was performed, including morphological, mechanical, physical, and thermal properties. The results showed that besides the processing method, the thickness was also controlled by the glycerol and water content, leading to density slightly above unity, with higher values for the optimum materials. The calendered films from the optimum formulations showed overall a higher number of cells and cell density than the controls. Higher elastic moduli and tensile strengths were obtained for the films from the optimum formulations made by either method because of the reinforcing effect of the tannic acid and nanoclays, but this led to lower strain at break. The thermal profiles were similar for all films, with higher stability for the optimum formulations. The results were also explained via chemical interactions between the components as observed by Fourier transform infrared spectroscopy. Overall, the optimum formulations not only produced better foamed films in terms of general properties but were much easier to process by both methods (calendering and blowing).

Dynamical Coupling between Connected Foam Films: Interface Transfer across the Menisci.

The highly confined flow of the liquid phase, trapped between the gas bubbles, is at the origin of the large effective viscosity of the liquid foams. Despite the industrial relevance of this complex fluid, the foam viscosity remains difficult to predict because of the lack of flow characterization at the bubble scale. Using an original deformable frame, we provide the first experimental evidence of the interface transfer between a compressed film (or a stretched film) and its first neighbor, across their common meniscus. We measure this transfer velocity, which is a key boundary condition for local flows in foams. We also show the dramatic film thickness variation induced by this interface transfer, which may play an important role in the film thickness distribution of a 3D foam sample.

Equilibrium thickness of foam films and adsorption of ions at surfaces: Water and aqueous solutions of sodium chloride, hydrochloric acid, and sodium hydroxide

HypothesisThe origin of negative surface charge at water/air interface is still not clear. The most probable origin is specific adsorption of OH− ions. From diffuse layer potential, we can evaluate the surface density of ions in the Stern layer which can be a measure for the specific adsorption of ions and determines whether the surface charge is solely due to the specific adsorption of OH− ions. ExperimentsEquilibrium thickness of foam films of pure water and aqueous solutions of NaCl, HCl, and NaOH was measured as a function of disjoining pressure for water and as a function of concentration for the aqueous solutions at 298.15 K. Quartz-glass cells thoroughly cleaned and immersed in pure water before use were used for the measurement. FindingsApplication of a modified Poisson-Boltzmann equation to the equilibrium film thickness gave the diffuse layer potential and the surface density of ions in the Stern layer. From the concentration dependence of the surface density, it was concluded that not only OH− ions but also Cl− ions and HCO3− and/or CO32− ions adsorb specifically at the water/air interface.

New structural approach to rationalize the foam film stability of oppositely charged polyelectrolyte/surfactant mixtures.

A novel structural framework is presented to rationalize the foam film stability of polyelectrolyte/surfactant mixtures using neutron reflectivity data. Provision of electrostatic or steric stabilization in thin foam films is related to the spatial distributions of molecules interacting from opposing air/water interfaces. The advance is discussed in the context of many studies on mixed systems over two decades that focused on macroscopic properties such as the surface tension, elasticity, potential and composition, but for which no robust correlations have been established. This concept can now be broadened to other colloidal dispersions of high impact for technical, environmental and life science applications.

Effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother

Froth stability is one of the most important factors in fine coal flotation as it significantly affects the separation efficiency. Diesel is always used as the flotation collector while the effect of diesel on the froth stability is less investigated. In this study, effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother was investigated. Three-phase and two-phase froth stability tests were first carried out and the negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The results of the three-phase dynamic froth stability showed that the maximum froth height and half-life of froth first increased and then decreased with the increase in diesel concentration. When diesel concentration increased to 8 kg/t, the maximum froth height and half-life of froth increased to 7.7 cm and 19 s. Deforming effect was observed when further increasing diesel dosage. Two-phase froth stability tests showed that the foaming ability and foam stability gradually decreased as the diesel concentration increased. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s, respectively. Single foam drainage tests showed that the diesel droplets dispersed into the middle of the foam film resulting in the formation of oil-bridge and rupture of the foam film. Meanwhile, the oil-film spreading pressure was found increased as the diesel concentration increased, directly indicating the antifoam effect of diesel. MIBC molecules were competitively adsorbed at diesel droplets, which reduced the effective concentration of the frother at the gas-water interface. Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified.

Rayleigh-Taylor-like instability in a foam film

A foam film is prepared in a controlled way, so that the top part of the film is much thicker than the bottom part. This situation is unstable under gravity and Rayleigh-Taylor-like fingers grow.The wavelength and the growth rate depend on the effective gravity and on the thick-film width.

Preparation of boron-doped diamond foam film for supercapacitor applications

A boron-doped diamond (BDD) electrode with surface nanostructure is fabricated by introducing SiO2 microspheres as a template on a Ta substrate via hot filament chemical vapor deposition (HFCVD). The improved specific active surface area and active materials enhance the availability of the electrochemically active sites, and improve the capacitive performance. Consequently, the fabricated BDD electrode with concentration ratio 2 of SiO2 and diamond powder (BDD-SD2) possesses smaller Rs, a maximum specific capacitance of 6.44 mF cm−2 at a current density of 0.10 mA cm−2, and good cycling stability with 83.1% retention over 3000 cycles. The influence mechanism of the fabricated BDD foam electrode on the capacitive performance is then revealed.

Tunable stability of oil-containing foam systems with different concentrations of SDS and hydrophobic silica nanoparticles

Experiment and molecular dynamics simulation were carried out to study the tunable stability of oil-containing SDS-stabilized Nitrogen-in-water foam. The experimental results show that the foam stability could be tuned by the concentrations of SDS and modified SiO2 nanoparticles. In the foam systems with a low SDS concentration (0.2 wt.%), the foams show poor stability and the foam stability was almost not affected by the addition of modified SiO2 nanoparticles. The foam stability was greatly improved at moderate SDS concentration (0.5 wt.%), it enhanced first and then weakened with the increase of modified SiO2 concentration, and the half-life time achieved a maximum value of 1292 s at 0.05 wt.% modified SiO2. However, at high SDS concentration (0.8 wt.%), the foam stability was pretty good except for when the modified SiO2 concentration is too high (>0.2 wt.%). The microscopic mechanism was obtained by investigating the structural and dynamic properties of the foam film. The simulation work showed consistent results of foam stability with the experimental results. Moreover, it also revealed that the concentration and configuration of SDS will affect its interaction with SiO2 and oil molecule, which is critical to foam stability.

Experimental investigation of amine-surfactant CO2 foam for smart mobility control during CO2 flooding

Amine-surfactant can be converted to be cationic surfactant in water solution saturated with CO2, which can enhance their foaming ability and foam stability, and the foaming ability can be switched off or on by CO2 or replacing with N2 with heating, so the amine-surfactants have great potential for smart mobility control to gas channeling during CO2 flooding. In this study, three alkyl propyl dimethylamines with different carbon chain length (R = 11, 17 and 22, named as UC11AMPM, UC17AMPM, and UC22AMPM, respectively), were investigated as CO2 responsive foam agent, and their foam performance under static and dynamic condition was tested up to 130 °C and 10.5 MPa using a visualized foam meter and a sand-pack flooding setup. The influence of carbon chain length on bulk solution viscosity, surface activity, foaming ability, and foam quality on bulk foam stability were measured and analyzed. The experimental results indicate that the three amine surfactants all demonstrate well CO2 responsibility and CO2 foaming ability, and show well switchable by CO2 and N2 at high temperature and high pressure (HTHP) condition. With the carbon chain length increasing, the surfactant shows higher absorption on the foam films, and bulk solution has a higher viscosity, which can decrease de-foam velocity and enhance the foam stability, as a result, the surfactant shows higher mobility control ability.