Air bubbles stabilization

E. Dickinson, et al. Factors controning the Formation-and Stability of Air Bubbles Stabilized by Partially Hydrophobic Silica Nanoparticles[J]. Langmuir, 2004, 20 8517-8525. 

E. Dickinson, R. Ettelaie, T. Kostakis, and B. S. Murray, "Factors controlling the for-mahon and stability of air bubbles stabilized by partially hydrophobic silica nanoparticles," Langmuir, 20 (2004) 8517-8525. 

The importance of the thin film between the mineral particle and the air bubble has been discussed in a review by Pugh and Manev [74]. In this paper, modem studies of thin films via SFA and interferometry are discussed. These film effects come into play in the stability of foams and froths. Johansson and Pugh have studied the stability of a froth with particles. Small (30-/ m), moderately hydrophobic 6c = 65°) quartz particles stabilized a froth, while more hydrophobic particles destabilized it and larger particles had less influence [75]. 

Defoamers. Foam is a common problem in papermaking systems (27). It is caused by surface-active agents which are present in the pulp slurry or in the chemical additives. In addition, partially hydrophobic soHd materials can function as foam stabilizers. Foam can exist as surface foam or as a combination of surface foam and entrained air bubbles. Surface foam usually can be removed by water or steam showers and causes few problems. Entrained air bubbles, however, can slow drainage of the stock and hence reduce machine speed. Another serious effect is the formation of translucent circular spots in the finished sheet caused by permanently entrained air. 

Frothers. These are also surface-active agents added to the flotation pulp primarily to stabilize the air bubbles for effective particle-bubble attachment, cariyover of particle-laden bubbles to the froth. 

Luft-bestandigkeit, /. stability in air, resistance to air. -bestandteil, m. constituent of air. -bild, n. aerial photograph (Optica) aerial image, -blaschen, n. (small) air bubble, -blase,/, air bubble air pocket air bladder, -bleiche, /. open-air bleaching, -bombe, /. aerial bomb, -brennstoffgemisch, n. fuel-air mixture. 

There several DO probes available. Some well-known branded fermenters, like New Brunswick, Bioflo series and the B. Braun Biotstat B fermenters are equipped with a DO meter. This unit has a 2 litre fermentation vessel equipped with DO meter and pH probe, antifoam sensor and level controllers for harvesting culture. The concentration of DO in the media is a function of temperature. The higher operating temperature would decrease the level of DO. A micro-sparger is used to provide sufficient small air bubbles. The air bubbles are stabilized in the media and the liquid phase is saturated with air. The availability of oxygen is major parameter to be considered in effective microbial cell growth rate. 

Bubble stability and breakup were reviewed by Hinze (H16). Early stages in the motion and breakup of two-dimensional air bubbles in water have been followed by Rowe and Partridge (R8), using high-speed cinephotography. The initial diameter of their circular bubble was about 4 in. 

The structure of whipped cream is quite complex. A coating of milk protein surrounds small globules of milk fat containing both solid and liquid fats. These globules stack into chains and nets around air bubbles. The air bubbles are also formed from the milk proteins, which create a thin membrane around the air pockets. The three-dimensional network of joined fat globules and protein films stabilizes the foam, keeping the whipped cream stiff. 

Salts of a-sulfo fatty acid esters can work as emulsifying agents for the preparation of asphalt emulsions and asphalt-latex emulsions. The ester sulfonates improve the storage stability of the emulsions [101,102]. In the manufacture of lightweight gypsum products air bubbles have to be mixed into the slurries. The use of salts of sulfonated C10 l8 fatty acid alkyl esters as foaming agents produces uniformly distributed fine bubbles [103]. Salts of C10 16 fatty acid alkyl ester sulfonates can also be added to cement mixtures to prevent slump loss of the mixtures [104]. 

The foaming capacity of milk is related to the ability to form stable air bubbles. One factor that can stabilize air bubbles is the presence of a film coating on... 

A typical characteristic of many food products is that these are multi-phase products. The arrangement of the different phases leads to a microstructure that determines the properties of the product. Mayonnaise, for example, is an emulsion of about 80% oil in water, stabilized by egg yolk protein. The size of the oil droplets determines the rheology of the mayonnaise, and hence, the mouthfeel and the consumer liking. Ice cream is a product that consists of four phases. Figure 1 shows this structure schematically. Air bubbles are dispersed in a water matrix containing sugar molecules and ice crystals. The air bubbles are stabilized by partial coalesced fat droplets. The mouthfeel of ice cream is determined by a combination of the air bubble size, the fat droplet size and the ice crystal size. 

The appearance of air bubbles in the polymer melt may occur under certain circumstances during processing. This phenomenon is rarely related to obvious faults in the polymer, but sometimes gas bubbles can be observed in cases of decreased thermal stability. Gas bubbles appear due to a certain amount of dispersed gas in the polymer matrix. Insufficient removal of gas from the extruder, particularly from the compression zone, can also cause the problem of air bubbles in the melt. An influence of the extruder screw could be established, because gas bubbles can be removed to some extent by using special screws or changing the extrusion conditions, along with the application of a vacuum. 

Source plates may be prepared in advance and stored frozen, depending upon fhe probe ink stability. In any case, source plates should be brought to ambient temperature to assure that all components have redissolved. We recommend that source plates be centrifuged to remove any entrapped air bubbles from fhe bottoms of the wells. While manual preparation of source plafes is possible, the use of a robotic dispensing sysfem is highly recommended in order to avoid mistakes in placement of fhe probe inks in fhe wells and to avoid cross-contamination. The use of such a device will also allow more xmiform preparation of subsequent source plates. 

While the microbubbles with an albumin shell were already in development, other groups of researchers investigated the use of surfactants or fipid-stabilized microbubble shells. Pluronic-stabifized renografin-air bubbles were prepared, but their storage stability was unsatisfactory. It required sonication shear mixing immediately prior to administration into experimental animals [18]. Other materials fared considerably better. A combination of a hydrophobic Span and... 

Therefore, the stability and lifetime of such thin films will be dependent on these different characteristics. This is evident from the fact that, as an air bubble is blown under the surface of a soap or detergent solution, it will rise up to the surface. It may remain at the surface if the speed is slow, or it may escape into the air as a soap bubble. Experiments show that a soap bubble consists of a very thin liquid him with an iridescent surface. But, as the huid drains away and the thickness decreases, the bubble approaches the equivalent of barely two surfactant molecules plus a few molecules of water. It is worth noting that the limiting thickness is of the order of two or more surfactant molecules. This means that one can see with the naked eye the molecular-size structures of thin liquid hlms (TLFs) (if curved). 

Bubbles are critical in manufacturing in the food industry. The stability and size of the bubbles determines the taste and the looks of the product. In industry, much research has been done on the factors that control bubble formation and stability. This is of special interest in the production of ice cream, where air bubbles are trapped in frozen material. 

As is known, if one blows air bubbles in pure water, no foam is formed. On the other hand, if a detergent or protein (amphiphile) is present in the system, adsorbed surfactant molecules at the interface produce foam or soap bubble. Foam can be characterized as a coarse dispersion of a gas in a liquid, where the gas is the major phase volume. The foam, or the lamina of liquid, will tend to contract due to its surface tension, and a low surface tension would thus be expected to be a necessary requirement for good foam-forming property. Furthermore, in order to be able to stabilize the lamina, it should be able to maintain slight differences of tension in its different regions. Therefore, it is also clear that a pure liquid, which has constant surface tension, cannot meet this requirement. The stability of such foams or bubbles has been related to monomolecular film structures and stability. For instance, foam stability has been shown to be related to surface elasticity or surface viscosity, qs, besides other interfacial forces. 

The stability of a gas (i.e., N2, C02, air) bubble in a solution depends on its dimensions. A bubble with a radius greater than a critical magnitude will continue to expand indefinitely and degassing of the solution would take place. Bubbles with a radius equal to the critical value would be in equilibrium, while bubbles with a radius less than the critical value would be able to redissolve in the bulk liquid. The magnitude of the critical radius, Rcr, varies with the degree of saturation of the liquid (i.e., the higher the level of supersaturation, the smaller the Rcr). The work, W, required for the formation of the bubble of radius Rcr is given by La Mer ... 

Ice cream emulsion has a very characteristic degree of stability. The air bubbles should remain dispersed, but as soon it melts in the mouth, the emulsion should break. This leads to the sensation of taste, which is very essential to enjoy its specialness. The sensation of taste on the surface of the tongue is known to be related to molecular shape and physicochemical properties. As soon as these molecules are separated from the emulsion, the taste sensation is recorded in the brain. Therefore, the various components must stay in the same phase after the breakup of the emulsion. Emulsifiers that are generally used have low HLB values (for W/O), and have been found to have considerable effect on the structure of the ice cream. 

Manufacturers of a multicomponent mixture of fatty acids, salts of sulfonic acid and stabilizing polar compounds (such as sodium octonate) claim that it provides concrete extra protection by creating ultra-stable air bubbles that are small and closely spaced [5]. In addition to many advantages, it can be used in fly ash concrete containing large amounts of... 

The air-bubble generating and stabilizing process requires a minimum paste consistency. Silica fume particles are smaller than those of Portland cement and addition of silica fume therefore increases the fine fraction of the particles. The higher fraction of smaller particles then increases the surface area causing a greater binding of the water in the mix. This removes the water required for the bubble-generating process. 

The basic mechanism of plasticizing effect on fresh cement mixes is explained by forming a temporarily stable double layer on cement particles. Since the formation of the double layer is also connected with the surface of particles, the increased demand for AEA, WRA and SP, in silica fume concrete and the decreased demand for AEA in the presence of a WRA or SP can be directly correlated to the specific surface increase of silica fume-cement blends and the dispersing action of WRAs and SPs in achieving a mortar consistency that enables the air-bubble-generating and stabilizing process [147, 149]. Concrete producers are now cognizant of the effect of these factors. Field silica fume concrete with a satisfactory, stable air-void system can therefore be produced consistently. 

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