Foaming ability and stability of silica nanoparticle-based triple-phase foam for oil fire extinguishing: experimental

The triple-phase foam has been widely used in oil fire extinguishing, and its two key parameters for application are the foaming ability and stability. We present a comprehensive study on the foam expansion ratio (FER) and drainage time, where factors such as the foam morphology, zeta potential of particles, foam mixing homogeneity, surfactant concentration, particle mass percentage, and specific surface area of the particle are investigated in detail. The dependence relationship curves of FER and drainage time with respect to the latter four variables are given through experiments, and optimal parameter values are selected. Moreover, the scaling laws correlating these variables are in agreement with the experimental results, and some necessary parameters are obtained by data fitting. These analyses are beneficial to better understand the foaming ability and stability mechanism of the triple-phase foam and to prepare materials of high performances for oil fire extinguishing.     

Implications of interfacial characteristics of food foaming agents in foam formulations

The manufacture of food dispersions (emulsions and foams) with specific quality attributes depends on the selection of the most appropriate raw materials and processing conditions. These dispersions being thermodynamically unstable require the use of emulsifiers (proteins, lipids, phospholipids, surfactants etc.). Emulsifiers typically coexist in the interfacial layer with specific functions in the processing and properties of the final product. The optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics - such as surface activity, amount adsorbed, structure, thickness, topography, ability to desorb (stability), lateral mobility, interactions between adsorbed molecules, ability to change conformation, interfacial rheological properties, etc. -, the kinetics of film formation and other associated physico-chemical properties at fluid interfaces. These monolayers constitute well defined systems for the analysis of food colloids at the micro- and nano-scale level, with several advantages for fundamental studies. In the present review we are concerned with the analysis of physico-chemical properties of emulsifier films at fluid interfaces in relation to foaming. Information about the above properties would be very helpful in the prediction of optimised formulations for food foams. We concluded that at surface pressures lower than that of monolayer saturation the foaming capacity is low, or even zero. A close relationship was observed between foaming capacity and the rate of diffusion of the foaming agent to the air-water interface. However, the foam stability correlates with the properties of the film at long-term adsorption.     

The effect of clay on foaming and mechanical properties of glass foam insulating material

In the current study, the main composition was prepared using soda-lime glass with dolomite [CaMg(CO₃)₂] as a foaming agent. The clay powder was added to the main composition in different ratios, and then, the mixtures were shaped by one-axial pressing. Differential thermal analysis (DTA) was used for the determination of crystallization temperatures, and the samples were heated according to the DTA results. Furthermore, heating microscopy was employed for studying the high-temperature behaviours of the mixtures. The samples were characterized using scanning electron microscopy, X-ray diffraction analysis, and comprehensive strength testing. Porosity and bulk density were measured to assess the foaming capability of the mixtures. The results showed that clay addition has a positive role on the mechanical properties of glass foam.     

A model for foam formation, stability, and breakdown in glass-melting furnaces

A dynamic model for describing the build-up and breakdown of a glass-melt foam is presented. The foam height is determined by the gas flux to the glass-melt surface and the drainage rate of the liquid lamellae between the gas bubbles. The drainage rate is determined by the average gas bubble radius and the physical properties of the glass melt: density, viscosity, surface tension, and interfacial mobility. Neither the assumption of a fully mobile nor the assumption of a fully immobile glass-melt interface describe the observed foam formation on glass melts adequately. The glass-melt interface appears partially mobile due to the presence of surface active species, e.g., sodium sulfate and silanol groups. The partial mobility can be represented by a single, glass-melt composition specific parameter psi. The value of psi can be estimated from gas bubble lifetime experiments under furnace conditions. With this parameter, laboratory experiments of foam build-up and breakdown in a glass melt are adequately described, qualitatively and quantitatively by a set of ordinary differential equations. An approximate explicit relationship for the prediction of the steady-state foam height is derived from the fundamental model.     

Improvement of foaming ability of egg white product by irradiation and its application

To investigate the enhancement of foaming abilities of liquid egg white (LEW) and egg white powder (EWP) by irradiation and its application for bakery product, LEW and EWP were irradiated at 0, 1, 2, and 5 kGy by Co-60 gamma ray. There was no pH change found among treatments in both LEW and EWP. The viscosity of LEW decreased significantly by irradiation (P<0.05), whereas that of EWP was not affected by irradiation. The foaming ability of LEW and EWP was significantly increased by irradiation as a dose-dependent manner (P<0.05). The volume and the height of angel cake baked with irradiated LEW were significantly higher than those of unirradiated control (P<0.05). For EWP, the volume and the height of angel cake were greater at 2 kGy only than those of control. A significant decrease in hardness, chewiness, and gumminess values and an increase in Hunter L* value were observed in the angel cakes prepared from irradiated egg white products (P<0.05). Results indicated that irradiation of egg white could offer advantages in increasing foaming ability and improving quality of final bakery products.     

Influence of the type of foam films and the type of surfactant on foam stability

The behaviour and the life time ( _p) of different types of foam films (thin liquid films, for which DLVO-theory is valid; common black films, Newton black films) have been studied as a function of external pressure (P), applied in the Plateau-Gibbs-borders of the foam. The foam stability and the course of thep/P-dependence are determined mainly by the type of the foam films. A criterion for estimation of foam stability is proposed on the base of the obtained experimental results.     

Relating foam lamella stability and surface dilational rheology

The surface dilational elasticity module E of a soluble cationic surfactant at the air-water interface is measured in a frequency range of 1-500 Hz. The data are then correlated with the lifetime of a foam lamella formed with the same surfactant solution. The surface rheological measurement have been performed with an improved design of the oscillating bubble technique that measures precisely the real and imaginary part of the complex dilational module E. The imaginary part captures a dissipative process which is interpreted as an intrinsic surface dilational viscosity kappa. The cationic surfactant 1-dodecyl-4-dimethylaminopyridinium bromide shows a transition between a surface elastic to a viscoelastic behavior with an increase of the bulk concentration. The transition corresponds to a striking increase in the lifetime of the foam lamella. The lamella lifetime of the viscoelastic system exceeds the one of an elastic system by 2 orders of magnitude while the absolute value of the E module remains comparable. The results suggest that surface dilational viscosity kappa is crucial for the ability of a surfactant system to form a stable foam. A simple picture that explains this observation is discussed.     

Effect of environmental humidity on static foam stability

The quality of foaming products (such as beer and shampoo) and the performance of industrial processes that harness foam (such as the froth flotation of minerals or the foam fractionation of proteins) depend upon foam stability. In this study, experiments are performed to study the effect of environmental humidity on the collapse of static foams. The dependency of the rate at which a foam collapses upon humidity is demonstrated, and we propose a hypothesis for bubble bursting due to Marangoni instability induced by nonuniform evaporation to help explain the dependency. This hypothesis is supported by direct experimental observations of the bursting process of isolated bubbles by high speed video recording and the thinning of isolated foam films under different values of humidity and temperature by microinterferometric methods.     

Effect of lidocaine on ovalbumin and egg albumin foam stability

Foam fractionation is a simple separation process that can remove and concentrate hydrophobic molecules such as proteins, surfactants, and organic wastes from an aqueous solution. Bovine serum albumin and ovalbumin have been widely used as model proteins due to their strong foaming potential and low price. Here, we study the effect of lidocaine on albumin foam, since drugs like lidocaine are known to bind with albumin. We observed that lidocaine not only enhances the amount of foam produced but also the stability of that foam as well. The foam stability was evaluated as the decay rate constant of the foam, determined from a change in height (or volume) of the foam over a given time period.     

烷基多苷的泡沫性能及在硬水中的稳定性研究

烷基多苷(APG)由葡萄糖的半缩醛羟基和脂肪醇羟基在酸催化下失去一分子水而得到,它与常用的阴离子表面活性剂十二烷基苯磺酸钠有相似的功能,其起泡性以及在硬水中的稳定性更优良。本文对实验室合成的部分烷基多苷产品的泡沫性能以及在硬水中的稳定性进行研究。     

The effect of filamentous bacteria on foam production and stability

Bacteria have been implicated in the formation of viscous brown foams that can appear suddenly on wastewater treatment plants. Three strains of the filamentous bacterium Gordonia amarae, isolated from wastewater treatment plants, were investigated to determine their effect on foam formation and stabilisation. During the exponential phase of the bacterial growth a biosurfactant was formed, causing a significant drop in the surface tension of the filtered medium and the formation of persistent foam. Foaming tests in the presence and absence of bacteria showed that bacteria increased foam persistence, most probably by reducing the drainage from the lamellae between bubbles. Experiments showed that > or =55% of the three bacterial strains partitioned into the foam produced by the biosurfactant, indicating that their surfaces were hydrophobic. The extent of partitioning was independent of the growth stage, suggesting that the cell surface hydrophobicity did not change with age, or with cell viability. This work shows that, although the G. amarae cells themselves do not cause foaming, they do produce biosurfactant, which aids foam formation, and they stabilise the foam by reducing the rate of drainage from the foam lamellae.     

Glass forming ability and thermal stability of oxyfluoride glasses

New oxyfluoride glasses based on the system ZrO₂-Pr₂O₃-ZrF₄-BaF₂ were obtained, and the glass forming ability of this system was evaluated. The effects of glass composition on both thermal stability and the crystalline phases formed upon heat treatment were determined by the DSC and XRD methods, respectively. The composition with higher thermal stability and better glass forming ability contained 2 mol% of oxides.     

On the stability of membrane,foam and emulsion bilayers with respect to rupture by hole nucleation

Bilayer membranes and bilayer foam or emulsion films were considered thermodynamically from a unified point of view as two-dimensional phases. The work of fluctuation formation of holes in a bilayer was determined and it was shown that the bilayer can be either stable or unstable with respect to rupture by hole nucleation. When the bilayer is in contact with a solution, its stability with respect to rupture was found to decrease with decreasing concentration of dissolved amphiphiles, and a limiting concentration was shown to exist, below which the bilayer is subject to rupture by hole nucleation. The connection is discussed between existing formulae for the work of fluctuation formation of holes in bilayers.     

Studies on foam stability by the actions of hydrophobically modified polyacrylamides

Hydrophobically modified polyacrylamide (HMPAM), as a foam stabilizer, was prepared with a cationic surfomer, acrylamide and acrylic acid by free-radical polymerization in aqueous solution. The actions of HMPAM on foam stability have been investigated with the Waring blender method. The results showed the foam containing HMPAM was stabler than that contained polyacrylamide. Moreover, a linear relationship between the logarithm of the half decay time and polymer concentration was observed, and the slope reflects the polymer ability to stabilize the foam.     

Combining foam injection molding with batch foaming to improve cell density and control cellular orientation via multiple gas dissolution and desorption processes

In contrast to solid parts fabricated through conventional injection molding (CIM), foamed parts manufactured via foam injection molding (FIM) exhibit substantial variations in mechanical properties, which are attributed to differences in the cellular structure. In this study, parts with different cellular structures are fabricated via FIM, during which the gas dissolution and desorption processes are controlled by subjecting the gas‐laden melt to reciprocating compression and expansion operations. The results suggest that the cell density can be drastically improved by rapidly decreasing the pressure caused by the mold opening and that the cell orientation obviously occurs in the direction perpendicular to the mold‐opening direction. Moreover, the cell density and cellular orientation can be adjusted by utilizing appropriate mold opening and closing operations, leading to improvements in the resultant ultimate mechanical properties. In particular, the foamed samples fabricated with controlled mold opening‐closing operations exhibit excellent tensile strength and strain‐at‐break, indicating that samples containing a high density of cells oriented along the tensile test direction facilitate the formation of superductility and an increase in tensile strength. Hence, a method that combines FIM with batch foaming has been proposed for improving the cellular structure and controlling the cellular orientation.     

Simulation of structure and stability of carbon nanoribbons

Results of carbon nanoribbons and nanotubes simulation by means of hybrid density functional method and using empirical potentials have been compared. Energy of the nanoribbons formation and their citting from graphene sheet as well as energy of the nanotubes folding from graphene and nanoribbons have been determined. The REBO force field satisfactorily reflects the result of quantum chemical simulations; however, it cannot reproduce the formation of triple bonds between the edge atoms of the nanoribbons in the armchair conformation and thus leads to underestimated stability of the latter. Energy of the nanotubes folding from the nanoribbons is linear with the nanotube diameter.     

Investigation of aqueous foam stability containing pigment colorant using polyoxyethylene nonionic surfactant

To improve foam stability in pigment foaming dispersions, a series of fatty alcohol polyoxyethylene ether (CmEOn) with different alkyl chain and ethylene oxide (EO) chain length (m = 12, 14, 16 and n = 5, 7, 9) were used as foam stabilizer to select the most superior structure for stabilizing foam. The effects of CmEOn on surface tension were investigated which revealed that the CMC of CmEOn in the pigment foaming dispersion decreased with the increase of surfactant hydrophobicity or the decrease of hydrophilicity. Compared to the alkyl chain, EO chain length influenced foam more significantly. C₁₄EO₅ in the pigment foaming dispersion showed lowest CMC and equilibrium surface tension. The presence of wormlike micelles and lamellar liquid crystal of SDS and C₁₄EO₅ endowed the C₁₄EO₅ pigment foaming dispersion with highest viscosity which was distinctly different with other CmEOn. C₁₄EO₅ showed the most superior stabilization effects with foam half-life of 172.9 min at 9 wt%. To further analyze the stabilization mechanism of C₁₄EO₅, the foam volume and bubble diameter change were observed with a digital microscope. The results demonstrated that the superior stabilization effects of C₁₄EO₅ were closely related to its high viscosity, which mainly resulted in the decrease of foam drainage and gas permeability. C₁₄EO₅, the optimal CmEOn structure for stabilizing foam, shows excellent foam stabilization capability in pigment foaming dispersions, which is a promising tool to realize pigment foam coloring.     

Foaming,foam films,antifoaming and defoaming

A general introduction to foams, the initial stages in the production of foams in aqueous solution, foam structures and the classification of bulk foams according to their lifetimes and stability are presented. Fundamental studies on horizontal and vertical isolated foam lamellae with emphasis on drainage and stability are reviewed. For freshly prepared foams containing fairly thick lamellae, the mechanical-dynamical properties of the surface adsorbed layers (surface tension gradients) are decisive for retaining stability. Important parameters to be taken into consideration are the surface elasticity, viscosity (bulk and surface), gravity drainage and capillary suction. Also the film should exhibit low permeability to gases. Providing the stability of a foam film (containing dilute surfactant) is retained during the initial dynamic drainage process, then eventually a static (equilibrium) situation will be reached at film thicknesses < 100 nm. In this region, interfacial interactions dominate and the stability of the film must be discussed in terms of the intermolecular forces (electrostatic double layer repulsion, dispersion force attraction and steric forces). This may lead to the formation of common black and Newton black films and these structures have been shown to be resilient to rupture and have low gas transfer characteristics. At high surfactant concentrations (>c.m.c.) stabilization of films and foams can occur by a micellar laying mechanism (stratification). Antifoaming and defoaming theories are presented, together with the mechanisms of heterogeneous antifoaming agents (non-polar oil, hydrophobic solid particles or mixtures of both) including recent theories describing the role of the emulsion and pseudo-emulsion film in the stability of foams containing oil droplets. Finally, defoaming by ultrasonic waves is briefly reviewed.