ABSTRACT
This chapter discusses the basic principles involved in the preparation of emulsions and their stabilization. The most common classes of emulsions are those whereby an oil is dispersed into water, referred to as oil-in-water (o/w) emulsions, or water dispersed into an oil, referred to as water-in-oil (w/o) emulsions. The selection of different surfactants in the preparation of either o/w or w/o emulsion is still made on empirical base. One of the earliest semiempirical scales for selecting an appropriate surfactant or blend of surfactants was proposed by Griffin and is usually referred to as the hydrophilic–lipophilic balance or HLB number. This scale is based on the relative percentage of hydrophilic to lipophilic groups in the surfactant molecule(s). K. Shinoda and coworkers found that many oil-in-water emulsions, when stabilized with nonionic surfactants, undergo a process of inversion at a critical temperature phase inversion temperature (PIT). They also showed that the PIT is influenced by the surfactant HLB number.
