#viscoelasticity

When flow moves past a cylinder, vortices get shed in its wake. Known as a von Karman vortex street, this distinctive pattern is seen behind flags, islands, and even behind starships.  (Image and research credit: U. Patel et al.)

Predicting When Ketchup Will Start Flowing

For a wide range of complex fluids, the transition from solid-like at rest to liquid-like when pushed can be predicted from properties of the at-rest state. [...] Complex fluids such as ketchup or toothpaste can switch from a solid-like state to a liquid-like state when subjected to a stress, such as shaking or squeezing. The details of this change can be crucial in areas such as food science and cosmetics. A research team has now shown that the point at which the solid-to-liquid transition occurs can be predicted from the properties of the substance while it is still a solid [1]. This insight could guide the design and control of this industrially important class of fluids.

Seven-year study uncovers the holy grail of beer brewing

For many people, a glass of beer feels incomplete without a thick, creamy layer of foam resting on top. Yet anyone who enjoys beer knows that this foam often disappears quickly, collapsing before the first sip. Some varieties, however, manage to hold their foam for a surprisingly long time. Researchers at ETH Zurich, led by Jan Vermant, Professor of Soft Materials, have uncovered the scientific explanation for these differences. Their work, published in the journal Physics of Fluids, is the result of seven years of detailed investigation. The idea for the study began with a straightforward question posed to a Belgian brewer: "How do you control brewing?" The brewer's answer was brief but revealing: "By watching the foam." The research team now has a solid grasp of the forces and structures responsible for long-lasting beer foam, offering new insight into what keeps a beer's head intact.