*3.2.1 Emulsion-diffusion/evaporation method*

Emulsion-diffusion is a technique that involves the emulsification of an organic phase onto an aqueous phase and the subsequent elimination of the organic solvent by diffusion into the external phase or driven by evaporation, which results in the formation of nanocapsules [6, 27]. The formation of a conventional oil-in-water emulsion within a partially water-soluble solvent via diffusion requires a second aqueous phase (also named dilution phase) that promotes the solvent to diffuse into the external phase causing polymer precipitation and interfacial phenomena, forming a core-shell structure. The homogenization of both phases can be attained through low or highenergy shaking (by means of magnetic or mechanical stirring, ultra turrax, ultrasound, high-pressure homogenizers, etc.), being the latter a better option to obtain smaller nanocapsules [5, 28]. The basis of this method, which differentiates it from nanoprecipitation, is mainly the use of an organic phase partially miscible in water and a polymer partially miscible in both phases. Some other factors that can affect the final characteristics of the nanocapsules obtained by this technique are the amount of dilution phase, the surfactant and polymer concentrations, the oil-to-polymer ratio, and the drop size of the primary emulsion [21]. The advantages of this method include better reproducibility, control of particle size, and therefore better scaling response; but enough energy must be spent to remove large amounts of water, and it is a recommended method only for particles with an oily core [5, 23, 29].
