Emulsification and Foaming

To make an emulsion or a foam, droplets or bubbles have to be generated from the interface between the two immiscible phases. This is usually done in a homogenizer, where droplets or bubbles continuously breakup and recoalesce. The droplet or bubble size is ultimately determined by the timescales of the breakup and recoalescence processes. Foams may also be produced by supersaturating a liquid with a gas. This can be realized by gas-producing microorganisms or by dissolving gas in a liquid under pressure, whereafter the pressure is released as happens when opening a bottle of beer. 

FIGURE 18.3 Interfacial tension gradients causing a liquid flow that opposes coalescence of emulsion droplets or foam bubbles. 

As a rule, the HLB number is sensitive to temperature variation. For most surfactants, HLB increases by raising the temperature, so that at a certain temperature a phase transition may take place. Thus, a w/o emulsion may invert into an o/w emulsion upon increasing the temperature. Around the phase inversion temperature, HLB == 7, which results in a rather unstable emulsion. 

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The main performance characteristics of light-duty liquids or dishwash blends are soil emulsification and foaming. Figueroa-Raulli [73] published a comparative study of AOS vs. alkyl sulfates (AS), alcohol ether sulfates (AES), and linear alkylbenzenesulfonates (LAS) in light-duty liquid blends. The blends were evaluated for flash foam, the stability of foam under accumulating soil loads, and for the number of plates washed. Blend performance is expressed as a percentage of a dishwash reference standard. 

Emulsification properties. Caseins and caseinates are commonly selected for food product applications that require surfactant properties, e.g., emulsification and foam stabilization, since they contain high protein contents of > 90 %, are highly soluble, and are resistant to heat-induced denaturatlon in products to be subjected to high temperature processing conditions (15). 

Applications Food plant cleaning, good emulsification and foam... 

A whey protein hydrolysate BioZate , containing ACE-inhibitory peptide was recently developed by Davisco Foods International Inc. The effect on blood pressure was studied with 30 unmedicated, non-smoking, borderline hypertensive men and women, and daily dose was 20 g. The results indicated that there was a significant drop in both systolic and diastolic blood pressure after 1-week treatment, which persisted throughout the study of 6 weeks. The application of this product is varied and flexible. In addition to the bioactive peptides, it has functional properties such as emulsification and foaming (Klink, 2002). 

Dilational moduli play an important part in a number of practical processes involving interfaclal area changes, where K° is a measure of the resistance a monolayer has against creating an interfaclal tension gradient Vy upon extension or compression. Emulsification and foam formation are representatives of such processes. On the other hand, once Vy has been created, the modulus controls the rate of relaxation. Historically, only static values have been considered. Recall that for elasticities of the Gibbs type, expressions for K° can be formulated on the basis of two-dimensional equations of state, see 13.4.30 and 30a]. In more modem developments the modulus is also studied under dynamic, or non-equilibrium... 

TABLE 11.2 Various Regimes for Emulsification and Foam Bubble Formation. Valid for Small Volume Fractions... 

Investigation of the role that liquid media play in the intensification of the grinding of solid materials is one of the main subjects of physico-chemical mechanics described in Chapter IX. The role of surfactants is equally important in the emulsification and foaming of liquids, which are processes broadly used in various technologies across the chemical, pharmaceutical, and food industries. 

The dynamic surface tension is an important property, relevant to many practical, non-equilibrium processes such as emulsification and foaming. Dynamic surface tension is a measure of how fast, in the millisecond range, a surfactant decreases the surface tension from the value of pure water (around 70 mN/m) to values in the range of 30 mN/m. It has been found that the type of spacer governs the dynamic surface tension of geminis to a considerable degree, i.e. the longer and... 

Toledan0,0. and Magdassi, S. (1998) Emulsification and foaming properties of hydrophobicaUy modified gelatin. /. Colloid Interf. Sci, 200,235. 

Alcohol ethoxysulfates have been used in field tests as nitrogen (177) and carbon dioxide (178) foaming agents. Field use of alcohol ethoxysulfates is restricted to low temperature formations owing to its limited hydrolytic stabihty at low pH and elevated temperature (179). It has been reported that some foams can reduce residual oil saturation, not by oil displacement, but by emulsification and imbibition of the oil into the foam (180). 

Apphcation chemists are most interested in physical and functional properties contributed by the sulfonate moiety, such as solubility, emulsification, wetting, foaming, and detersive properties. Products can be designed to meet various criteria including water solubility, water dispersibility, and oil solubility. The polar SO moiety contributes detersive properties to lube oil sulfonates and dry-cleaning sulfonates. 

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

Fuel system corrosion inhibitors must have a low tendency toward emulsification with water and toward foam enhancement in turbulent systems. These properties are especially critical whenever inhibitors are used in jet fuel. The sensitivity of jet fuel pumping and injection systems requires that fuel be free of emulsions and foam. 

Foams. See under Emulsification, Emulsion, Foaming and Foam in Vol 5, p E87-R Addnl Ref J.J. Bickerraan et al, "Foams. Theory and Application , Reinhold, NY(1953)... 

It is essential to consider the physico-chemical properties of each WPC and casein product in order to effectively evaluate their emulsification properties. Otherwise, results merely indicate the previous processing conditions rather than the inherent functional properties for these various products. Those processing treatments that promote protein denaturatlon, protein-protein Interaction via disulfide interchange, enzymatic modification and other basic alterations in the physico-chemical properties of the proteins will often result in protein products with unsatisfactory emulsification properties, since they would lack the ability to unfold at the emulsion interface and thus would be unable to function. It is recommended that those factors normally considered for production of protein products to be used in foam formation and foam stabilization be considered also, since both phenomena possess similar physico-chemical and functionality requirements (30,31). 

Figure 1.5 shows an example of an aqueous foam with emulsified and imbibed crude oil droplets residing in its plateau borders. Using a simple model the degree of emulsification and imbibition has been found to correlate quite well with foam sensitivity to oil for a wide variety of foams, oils, and conditions [114]. A limitation of emulsification/imbibition models is that they will only be important for foam lamellae that are thick enough to accommodate realistic emulsion droplet sizes. Typical foam lamellae in porous media appear to have thicknesses on the order of tens of nm [70,71,114,328],... 

The adsorption mechanisms of surfactant at interfaces have been extensively studied in order to understand their performance in many processes such as dispersion, coating, emulsification, foaming and detergency. These interfaces are liquid-gas (foaming), liquid-liquid (emulsification) and liquid-solid (dispersion, coating and detergency). 

The rating scheme was biased towards Emulsification and Emulsion Stability. The use pattern for the product under study was the guide for this bias. These two properties were considered more important in the performance of the product than foam or spontaneity. 

Nearly all of the treatment processes in which fluids are injected into oil wells to increase or restore the levels of production make use of surface-active agents (surfactant) in some of their various applications, e.g., surface tension reduction, formation and stabilization of foam, anti-sludging, prevention of emulsification, and mobility control for gases or steam injection. The question that sometimes arises is whether the level of surfactant added to the injection fluids is sufficient to ensure that enough surfactant reaches the region of treatment. Some of the mechanisms which may reduce the surfactant concentration in the fluid are precipitation with other components of the fluid, thermally induced partition into the various coexisting phases in an oil-well treatment, and adsorption onto the reservoir walls or mineral... 

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