“Oobleck” still holds some surprises

Oobleck, a whimsical mixture of corn starch and water, continues to captivate scientists with its unexpected behaviors. When combined in the right proportions, this fascinating substance flows easily when stirred slowly but behaves like a solid when struck—earning its colorful name from a 1949 Dr. Seuss book. Recent research published in the journal Physical Review Letters has unveiled intriguing properties of oobleck, particularly its behavior upon impact with flat surfaces. Unlike ideal fluids, where viscosity remains consistent regardless of external forces, oobleck is a non-Newtonian fluid. This means its viscosity alters in response to applied strain or shearing forces, bridging the gap between liquid and solid states. In contrast to water, which flows unimpeded by stirring or mixing, non-Newtonian fluids such as oobleck respond differently. For example, ketchup is another shear-thickening non-Newtonian fluid; tapping the bottle doesn't speed up its flow because the force increases its viscosity. Other common examples include yogurt, gravy, and thick pie fillings. The complex physics underlying oobleck are not only surprising but also a source of fascination for researchers. In 2023, molecular engineers from the University of Chicago explored these principles using dense suspensions of piezoelectric nanoparticles, providing insights into the molecular dynamics that govern oobleck's transition from liquid to solid states.