Theories of Emulsification

Surface Tension Theory

• Liquids tend to minimize their surface area by forming spherical shapes, which have the least surface area.
• Surface tension is a force that resists the formation of smaller droplets when two immiscible liquids come into contact.
• Emulsifying agents reduce interfacial tension, diminishing the repellent force between the liquids and each liquid's attraction to its own molecules.
• Emulsifiers lower the interfacial tension, facilitating the breaking up of large globules into smaller ones, which then have a lesser tendency to reunite or coalesce.

Oriented-Wedge Theory

• Emulsifying agents form monomolecular layers around the droplets of the internal phase.
• Emulsifying agents are preferentially soluble in one of the phases and are embedded more deeply in that phase than the other.
• Molecules with a hydrophilic and hydrophobic portion orient themselves in each phase based on their solubility.
• Hydrophilic emulsifiers promote o/w emulsions, while hydrophobic emulsifiers favor w/o emulsions.
• The phase in which the emulsifier is more soluble becomes the continuous phase of the emulsion.

Plastic or Interfacial Film Theory

• Emulsifying agents form a thin film at the interface between the immiscible liquids, adsorbed on the surface of internal phase droplets.
• The film acts as a barrier, preventing contact and coalescence of the dispersed phase.
• The stability of the emulsion depends on the toughness and flexibility of this film.
• The degree of solubility of the emulsifying agent in the two phases determines whether o/w or w/o emulsions are formed.