Emulsion stability, effect

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

The repulsion between oil droplets will be more effective in preventing flocculation Ae greater the thickness of the diffuse layer and the greater the value of 0. the surface potential. These two quantities depend oppositely on the electrolyte concentration, however. The total surface potential should increase with electrolyte concentration, since the absolute excess of anions over cations in the oil phase should increase. On the other hand, the half-thickness of the double layer decreases with increasing electrolyte concentration. The plot of emulsion stability versus electrolyte concentration may thus go through a maximum. 

Partially hydrolyzed poly(vinyl alcohol) grades are preferred because they have a hydrophobic /hydrophilic balance that make them uniquely suited for emulsion polymerization. The compatibUity of the residual acetate units with the poly(vinyl acetate) latex particles partly explains the observed stabilization effect. The amount of PVA employed is normally 4—10% on the weight of vinyl acetate monomer. The viscosity of the resulting latex increases with increasing molecular weight and decreasing hydrolysis of the PVA (318). 

Where employed for BW applications, silicone emulsion strengths, emulsion stability, spreading coefficients, and effectiveness rates may vary considerably and the preferred product should be identified by comparative evaluation. 

Carboxypolymethylene also exerts a stabilizing effect on a cetyl alcohol-sodium lauryl sulfate emulsion containing 15% of talc. The differential in the distribution of particles at all levels of those stabilized systems discussed above can be considered negligible for all practical purposes. 

Water content and viscosity measurements in certain systems show a correlation to emulsion stability [597]. The viscosity provides a more reliable measure of emulsion stability, but measurements of the water content are more convenient. Mixing time, agent amount, settling time, and mixing energy impact the effectiveness of an emulsifier. 

The major problem in demulsifying crude oil emulsions is the extreme sensitivity to demulsifier composition. There have been attempts (2, 3) to correlate demulsifier effectiveness with some of the physical properties governing emulsion stability. However, our understanding in this area is still limited. Consequently, demulsifier selection has been traditionally based on a trial and error method with hundreds of chemicals in the field. 

Our goal is to develop a property-performance relationship for different types of demulsifiers. The important interfacial properties governing water-in-oil emulsion stability are shear viscosity, dynamic tension and dilational elasticity. We have studied the relative importance of these parameters in demulsification. In this paper, some of the results of our study are presented. In particular, we have found that to be effective, a demulsifier must lower the dynamic interfacial tension gradient and its ability to do so depends on the rate of unclustering of the ethylene oxide groups at the oil-water interface. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

An emulsion is a dispersed system of two immiscible phases. Emulsions are present in several food systems. In general, the disperse phase in an emulsion is normally in globules 0.1-10 microns in diameter. Emulsions are commonly classed as either oil in water (O/W) or water in oil (W/O). In sugar confectionery, O/W emulsions are most usually encountered, or perhaps more accurately, oil in sugar syrup. One of the most important properties of an emulsion is its stability, normally referred to as its emulsion stability. Emulsions normally break by one of three processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation originate in density differences between the two phases. Emulsions often break by a mixture of the processes. The time it takes for an emulsion to break can vary from seconds to years. Emulsions are not normally inherently stable since they are not a thermodynamic state of matter. A stable emulsion normally needs some material to make the emulsion stable. Food law complicates this issue since various substances are listed as emulsifiers and stabilisers. Unfortunately, some natural substances that are extremely effective as emulsifiers in practice are not emulsifiers in law. An examination of those materials that do stabilise emulsions allows them to be classified as follows ... 

Surfactants such as sulfated fatty alcohols may be hydrated to a higher extent than the fatty alcohols alone and thus stabilize o/w emulsions. The eombination of an anionic and a nonionic srrrfactant has proved to be partieularly effeetive, sinee the electrostatic repulsion forces between the ionie surfaetant moleeules at the interface are reduced by the incorporation of nonionic molecules, thus improving the emulsion stability. The combination of cetyl/stearyl sulfate (Lanette E) and eetyl/ stearyl alcohol (Lanette 0) to yield an emulsifying eetyl/stearyl aleohol (Lanette N) is an example of this approach. The polar properties of this srrrfactant mixtrrre are dominant, and o/w creams are formed. In contrast to w/o systems, the stabilizing effect of the surfactant mixtirre is not mainly due to adsorption at the interfaee. Instead, the mixed surfactants are highly hydrated and fonn a lamellar network, whieh is... 

Binks BP, Lumsdon SO. Pickering emulsions stabilized by monodisperse latex particles effects of particle size. Langmuir 2001 17 4540-4547. 

Shinoda K, Aral H (1967) The effect of phase voliune on the phase inversion temperature of emulsions stabilized with nonionic simfacatnts. J Colloid Interface Sci... 

The foam stability of mixed AEg with a middle chain length distribution is better than the individual lower one. Among all AEg, the mixed Cio,12 9 gives probably the best result on the stability of emulsion to caster oil. Introducing a long hydrocarbon chain in the mixture or a wide distribution in hydrocarbon chain length causes no effect on the emulsion stability (Figure 6). 

In a previous paper 8), was inferred for com oil-in-water as well as toluene-in-water emulsions stabilize by bovine serum albumin (BSA). The effects of pH, ionic strength and BSA concentration on Hmax were investigated. Comparison of experimental maximum disjoining pressure witii predicted Ilmax indicated that steric interaction is the predominant mechanism of stabilization in such systems. 

Aquatic seeds in irrigation ditches interfere with the flow of water and often result in serious loss to farmers. Chlorinated benzene with appropriate emulsion stabilizers has proved effective in the control of such weeds. The Bureau of Reclamation through its Denver laboratories tested methyl substituted benzenes and found them equally toxic to aquatic weeds. As a result, the aromatic solvents, both from coal and petroleum sources, are proving a boon to farmers. 

Increasing temperature has the effect of decreasing emulsion stability this has been demonstrated by Kunieda et al. [11,14], among others, and is due to the increase of the rate of coalescence of the dispersed phase droplets with increasing thermal energy. Pons et al. [100] also noted that a temperature increase caused an increase in average droplet size due to increasing interfacial tension. 

Semenova, M.G., Antipova, A.S., Belyakova, L.E., Dickinson, E., Brown, R., Pelan, E., Norton, I. (1999). Effect of pectinate on properties of oil-in-water emulsions stabilized by asi-casein and P-casein. In Dickinson, E., Rodriguez Patino, J.M. (Eds). FoodEmul-sions and Foams Interfaces, Interactions and Stability, Cambridge, UK Royal Society of Chemistry, pp. 163-175. 

---