Emulsion and Foam Stability

Following the formation stage, emulsions and foams are subjected to various processes that influence their long-term stability, notably their colloid stability, their particle size, and their particle-size distribution. The major processes, which are often correlated, are briefly reviewed. 

---

The surface active properties of aHphatic amine oxides were discovered ia the 1930s and the wetting, detergent, emulsion, and foam stabilizing properties were published shortiy thereafter (42). However, the use of amine oxides was not significant until Procter and Gamble started usiag them ia household products around 1960 (43—46). 

There is now a solid body of available knowledge to indicate that the general features of biopolymer self-assembly in bulk aqueous solutions can account for various detailed aspects of the stability, rheology and microstructure of oil-in-water emulsions (and foams) stabilized by the same kinds of biopolymers (Dickinson, 1997, 1998 Casanova and Dickinson, 1998 Dickinson et al., 1997, 1998 Semenova et al., 1999, 2006 van der Linden, 2006 Semenova, 2007 Ruis et al., 2007). In particular, the richness of the self-assembly and surface-active properties of the... 

Malhotra, A.K. Wasan, D.T. Interfacial Rheological Properties of Adsorbed Surfactant Films with Applications to Emulsion and Foam Stability in Thin Liquid Films, Ivanov, I.B. (Ed.), Dekker New York, 1988, pp. 829-890. 

Very varied functionality is typical of biopolymers as main materials of life and of food. Functional roles in foods cover such applications as water binding, solubility and viscosity, catalysis, lipid and flavour adsorption, emulsion and foam stabilization, gel and film forming. Additionally, they provide biodegradable ingredients and materials, nutrients, vaccines, adaptogens, carriers and delivery of micro- and macronutrients, and so on. 

Murray, B.S. Interfacial rheology of mixed food protein and surfactant adsorption layers with respect to emulsion and foam stability. Proteins at Liquid Interfaces, D. Mobius and R. Miller, eds., Elsevier, Amsterdam, 1998. 

Malhotra AK, Wasan DT. Interfacial rheological properties of adsorbed surfactant films with applications to emulsion and foam stability. In Ivanov IB, ed. Thin Liquid Films, Fundamentals and Applications. Vol. 29. Surfactant Science Series. New York Marcel Dekker, 1988 829-890. 

Lipamide. [lipo] Fatfy add alkanol-amide emulsifier, opacifier, thickener, emulsion and foam stabilizer, lubricant, humectant, antistat for personal care prods. 

The presence of mixed surfactant adsorption seems to be a factor in obtaining films with very viscous surfaces [27], For example, in some cases, the addition of a small amount of nonionic surfactant to a solution of anionic surfactant can enhance foam stability due to the formation of a viscous surface layer possibly a liquid crystalline surface phase in equilibrium with a bulk isotropic solution phase [21, 126], To the extent that viscosity and surface viscosity influence emulsion and foam stability one would predict that stability would vary according to the effect of temperature on the viscosity. Thus, some petroleum industry processes exhibit serious foaming problems at low process temperatures, which disappear at higher temperatures [21],... 

With parameter values typical for foams, a = 30 dyn/cm and Rc = 50 xm, and with the buoyancy as the driving force, from Eq. (246) one obtains hi = 14 nm, which is an uirrealistically small value. This means that the buoyancy force might be insuflicient to explain the formation of films during the hydrodynamic interaction of two bubbles. Another outer force that can be important for the emulsion and foam stability is the hydro-dynamic force in a shear or nonturbulent flows [461]. An attempt to treat the case of turbulence was performed by Kumar et al. [462,463]. For micron-sized liquid droplets. 

The most effective emulsion and foam stabilizers are aerosol systems containing fluorocarbon propellants as surfactants. These are believed to form an oriented polymolecular structure at the propellant-water interface for optimum stability Sanders has found [90] that the surfactants must have a low solubility in both phases and have the ability to remain in the interfacial region. Hydrocarbon and fluorocarbon chains are not freely miscible and this perhaps explains the unusual behaviour of the surfactants in these systems. Addition of long-chain alcohols or acids enhance stability of the fluorocarbon emulsions and a hypothetical structure of the interfacial region has been proposed (Fig. 8.16). Davis et al. [91] have investigated the stability of fluorocarbon emulsions intended as artificial blood substitutes. Perfluorocarbon oils tended to produce unstable emulsions while oil phases such as perfluorotributylamine or per-fluorotetrahydrofuran formed more stable systems. These authors also refer to the possibility that as fluorocarbon-hydrocarbon mixtures have positive excess free energies, cohesive and adhesive forces between surfactant and oil phase will result. 

P Walstra. Overview of emulsion and foam stability. In E Dickinson, ed. Food Emulsions and Foams. London Roy Soc Chem, 1987. 

Solid Particles at Liquid Interfaces, Including Their Effects on Emulsion and Foam Stability... 

---