Tiny Bubbles, Stabilized

Micrometer-sized bubbles favorably affect the taste, smell, and texture of foods and cosmetics, but the bubbles are unstable and don't last long. Now researchers have devised a method to stabilize bubbles in liquids so they'll last for more than a year. Harvard University professor Howard A. Stone, graduate student Emilie Dressaire, and colleagues at Unilever Research & Development in Trumbull, Conn., led by Rodney Bee carried out the work (Science 2008, 320, 1198). The researchers mix viscous glucose syrup with water and sucrose stearate, a surfactant, for two hours. Large bubbles of air initially trapped in the mixture are broken into smaller bubbles by shear forces in the mixer. The surfactant stabilizes the resulting micrometer-sized bubbles by forming an insoluble, elastic shell at the air-liquid interface. The shell gradually adopts a honeycomb structure with nanometer-scale hexagonal patterns. In addition to food and other multiphase material applications, stabilized bubbles could be useful as ultrasound contrast agents, Dressaire notes.