Fundamentals of emulsion formation and stability

This chapter describes the fundamental aspects of emulsion formation and of their stability, intended to provide a solid background for the reader to comprehend the more advanced concepts that will be presented over the next chapters. Emulsions are presented along their classical categorization regarding droplet size and type, including multiple emulsions. Physical–chemical aspects of macroemulsions formation are described, elucidating the origin of their thermodynamic instability, but also addressing the key aspects that may be used to ensure their kinetic stability. The physical mechanisms leading to their instability, such as creaming, sedimentation, flocculation, coalescence, and Ostwald ripening, are also explained. Finally, strategies on how to overcome this instability are illustrated, including high- and low-energy emulsification techniques, the parameters to guide the correct choice of emulsifiers, mostly the HLB concept, and other formulation aspects related to their electrostatic and steric stabilization, as well as the addition of rheology modifiers.