Emulsion structure and stability

Another important emulsion structure parameter is the mean diameter of the droplets (d) which determines their dispersity. It is common to call disperse systems having d 0.1 pm among the so-called macroemulsions . Microemulsions are thermodynamically stable disperse systems many investigators name them homogeneous, others consider them microheterogeneous [39—41]. Achievement of extremely low (y 0.1 mN/m) interfacial tensions is a prerequisite to obtain microemulsions. 

The coalescence rate, i.e. formation of larger droplets after collision of two droplets, depends on the number of collisions and on the properties of the adsorption layers. For dilute emulsions, as well as emulsions having V2 = 0.3—0.74, coalescence is the main process leading to the disturbance of their aggregative stability. Hence, prerequisite for the production of appreciable volumes of any type of emulsions suitable for practical application is provision of their coalescence stability. In case of o/w emulsions, maximum stability against coalescence is achieved through the formation, on the surface of the disperse phase particles, of structured adsorption layers, a structure-mechanical barrier defined by Rehbinder [8]. Such layers are 

In case of a constant contact of emulsion droplets, which is typical of highly concentrated systems, diffusive transfer (isothermal distillation, recondensation, Ostwald ripening) is of great importance, along with coalescence. This phenomenon has been extensively studied in [46- 7]. 

The flocculation process is less investigated with respect to emulsions, especially water-in-oil emulsions. According to the DLVO theory [48] the aggregation stability of a disperse system is determined by the sum of energy of ion-electrostatic repulsion (Uj) and Van-der-Waals attraction (Um) 

The terms of this sum depend on the distance (h) between the particles, Um falling proportionally (h ) with increasing distance, while Uj decreases exponentially. There are, as a rule, two minima in the energetic curves reflecting the interaction between two particles as a 

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