Emulsifier critical micelle temperature

Fig. 8.15. Solubility of an emulsifier in water. Ordinate concentration, abscissa temperature. I Solution, II Crystals, III Micelles, Tci Critical micelle temperature...

Like other emulsifiers, an EUP forms micelles at a critical micelle concentration (CMC). For comonomer-free EUP-emulsions of the (MA+HD)- type the CMC is about 5 X 10"4 g/ml [115,118]. The CMC depends on the composition and chain length of the polyester, the presence of an electrolyte [118] and the temperature. 

K. Taiwo, H. Karbstein, and H. Schubert [/. Food Process Eng., 20, 1-16 (1997)] studied the influence of temperature on the kinetics of adsorption of a variety of food emulsifiers at oil-water interfaces. They used interfacial tension measurements to monitor the rate at which egg yolk present at 10 times its critical micelle concentration was transferred to a water-soybean oil interface. The rates of these processes are important in assessing the potential stability of oil-in-water emulsions of the type found in salad dressings and mayonnaise. The interfacial tension can be viewed as a property that reflects the contributions of the various species present at the interface, being an additive function of these contributions. Each individual contribution is proportional to the quantity of the material in question located at the interface between the oil and the water. The reaction of interest can be regarded as... 

The melting properties are of crucial importance to the technical functionality of emulsifiers, in addition to their amphiphilic properties. Most food and feed emulsifiers are based on natural fat sources, thus giving different melting properties. The consequences of the melting properties can be expressed as the Krafft temperature (i.e. the temperature at which the solubility is above the critical micelle concentration) or as the transition temperature (chain melting temperature, i.e. the melting temperature of the fatty acids in a semicrystaline bilayer). The transition temperature in an emulsifier water system forming a lamellar liquid crystalline phase... 

The temperature at which the solubility of an groups are oriented towards the inner water emulsifier reaches the CMC is called the critical phase, micelle temperature (Tc, Krafft point). Crystals, micelles, and the dissolved emulsifier are in equilibrium at the Tc (Fig. 8.15). An emulsifier cannot form micelles below the Tc which, e. g., depends on the structure of the fatty acid residues in... 

Because the effective HLB of a given surfactant will depend on the nature of the solvent, HLB numbers cannot be considered to be absolute, reaUstic measures of the emulsifying ability of a material under all conditions. The actual HLB of a surfactant in a system will depend on the nature of the solvent, the temperature, and the presence of additives such as cosolvents, electrolytes, and polymers. Although the relationship will not always be linear, the HLB may be expected to vary in a manner analogous to that found for the critical micelle concentration of the surfactant under the same conditions. 

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