Emulsion formation is a challenging task. Breaking a large drop into smaller fragments gives rise to an increase in the total interfacial area and, consequently, in the interfacial energy. External energy must, therefore, be supplied to form an emulsion. Nanoemulsion formation is even more challenging since small drops require even higher interfacial energy.
The high-energy methods are designed to supply the energy required for emulsification by subjecting it to a disruptive hydrodynamic stress, that is, laminar or turbulent shear or cavitation. This chapter provides an overview of the current understanding of the mechanical principles of the high-energy methods. It discusses how they give rise to emulsification, both in terms of the traditional stress-balance description and of dynamic theories of emulsification. Special emphasis is placed on the difference between forming micrometer range emulsions and nanoemulsions.