Liquid crystals and emulsion stability

The presence of liquid-crystalline phases at the oil-water interface has been shown to produce improvements in the stability of various emulsions, although the exact mechanism of their action is still subject to some question. 

FIGURE 11.4. In a manner similar to stabilization by cxrlloidal particles, surfactant Uquid crystals may adsorb at the emulsion interface and provide mechanical, steric, and/or electrostatic stabilization. 

Even in the absence of complete understanding, the use of hquid crystals at o/w interfaces has been demonstrated in practical apphcations. 

It has been found that the presence of two surfactant species, one water and the other oil soluble, can greatly enhance the stability of an emulsion system. The effect has been explained by invoking two possible mechanisms (1) to the production of very low interfacial tensions through a synergistic effect that increases the effectiveness of adsorption of the combination and (2) the formation of cooperative surfactant complexes, which impart greater strength (i.e., a more effective energy barrier to flocculation) to the o/w interface. 

An interfacial complex may be defined as an association of two or more surface-active molecules at an interface in a relationship that does not exist in either of the bulk phases (Fig. 11.5). Each bulk phase must contain at least one component of the complex, although the presence of both in any one phase is not ruled out. According to le Chatelier s principle, the formation of 

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