GRAVITATIONAL SYNERESIS IN FOAMS AND CONCENTRATED EMULSIONS

When a concentrated gas-liquid foam or liquid-liquid emulsion is held in a container, drainage may or may not result in the separation of a layer of bulk continuous phase. This study establishes precise criteria for the occurrence and extent of such "gravitational syneresis." Factors that promote syneresis are relatively low volume fraction of the dispersed phase, large sample height (tall container), large mean drop size, low interfacial tension, high-density difference between the phases, and a container that is wider at the top than at the bottom. Procedures are presented for the quantitative evaluation of the vertical gradient in the volume fraction at equilibrium. © 1990.