In microencapsulation, each emulsion component has differing electrical properties. The solvent and carrier, being the most conductive of the group, will pick up the most electrons. The active, being less conductive, will pick up fewer electrons. The solvent molecules have the greatest charge density and will repel each other. This will force the solvent and carrier to migrate to the outer surface of the droplet, while the active will remain at the center.
Driving the solvent to the outer surface creates the ideal drying condition, leading to a near perfect encapsulation of the active without the use of high evaporation temperatures.
Spray Drying Technology has been in use on an industrial scale since the late 19th Century. In that time, the technology has evolved only incrementally with the fundamentals remaining very much the same still today.
Typically, this process uses an emulsion made up of three components; a solvent (water or solvent), a carrier (starch), and a core/active (oil or vitamin). The object of Spray Drying is microencapsulation - forming the carrier around the active and drying off the solvent with a heated drying gas. Ideally, the carrier remains as a protective layer around the active keeping it from oxidizing.Traditionally, the emulsion is atomized using a nozzle or rotary atomizer and heated drying gas (200°C) is introduced to the atomized emulsion.
Some major draw-backs of traditional spray dry include intense heat that can degrade the end product, and a dried particle that has the active trapped both inside the droplet and on the surface, partially defeating the intention of microencapsulation.