Being able to reversibly generate stable emulsions could help facilitate syntheses, separations, and processing of a variety of chemicals. Philip G. Jessop of Queen's University, Kingston, Ontario, and his colleagues have made this possible by creating "switchable surfactants" that need only CO2 and air to turn on and off (Science 2006, 313, 958). A year ago, Jessop's group reported switchable solvent systems based on the same concept (C&EN, Aug. 29, 2005, page 27). The researchers used long-chain alkylamidines RN=CR'-NR'2, where R is C12H25 or C16H33 and R' is methyl—that form bicarbonate salts when mixed with water and CO2 is added. The in situ salt formation helps create stable emulsions. Bubbling air into the mixture releases CO2 and breaks the emulsion. Switchable surfactants can be considered for all process applications involving surfactants, including emulsion polymerizations and different aspects of crude oil processing, Jessop notes.