History

The term coacervation is derived from the latin acervus, meaning aggregation, and the prefix co to indicate union of colloidal particles. Bungenberg de Jong and Kruyt described the term in 1929 and 1930, as noted by Bungenberg de Jong (1949a). Two chapters, 'Crystallization -Coacervation - Flocculation' and 'Complex Colloidal Systems' describing the early work of coacervation, were prepared by Bungenberg de Jong (1949a,b). The term was used to indicate the formation of colloid rich liquids brought about by various processes which caused phase separation in aqueous systems of macromolecules or colloids in solution.

In 1954, Green and associates of the National Cash Register Company researched the coacervation process using gelatin and gelatin-acacia for commercial purposes. This led to the publication of a number of patents for the preparation of carbonless carbon paper. The result of the coacervation process was the formation of microcapsules containing a colourless dye precursor. The microcapsules were attached to the underside of the paper, and the dye was released upon pressure from pencil or pen and reacted with an acid clay which coated the top surface of the subsequent page; a copy was formed as a result (Deasy, 1984a; Kondo, 1979b).

A brief history of the process using phase separation by emulsification and/or solvent evaporation/extraction is provided by Arshady (1990b), who indicates that early examples include the formation of microspheres/ microcapsules of cellulose beads by Wieland and Determan in 1968, and that of dye-loaded polystyrene microcapsules by Vranken and Claeys in 1970. An extensive list of early patents is provided by Kondo (1979a).

The preparation of microcapsules is the single, most important use of coacervation-phase separation because microcapsules are widely used in many industries such as printing, food, aerospace, agriculture, cosmetics, and especially pharmaceuticals. Other methods of microencapsulation have been investigated and are used extensively. The two other principal methods of microencapsulation are chemical processes which include interfacial polymerization and in situ polymerization and also mechanical processes which include, for example, air suspension coating and spray drying (Kondo, 1979c; Deasy, 1984c).

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