https://journals.aps.org/prl/abstract/10.1103/t2vy-32wr Comments URL: https://news.ycombinator.com/item?id=48877668 Points: 88 # Comments: 45

When pulled at 100 millimeters per second, a blend of hydrogen and carbon stretches. At 300 millimeters per second, the fluid breaks. Adapted with permission from Phys. Rev. Lett. 136, 124002. Copyrighted by the American Physical Society. Thamires Lima, a research professor in chemical engineering at Drexel University, studies the properties of thick, viscous liquids — think honey or molasses, though in a lab you’re more likely to find polypropylene or crude oil. Using a method called extensional rheology, Lima stretches liquids between metal plates to find the force that makes them flow. A few years ago, she was conducting a test as part of a project in collaboration with the oil and gas company Exxon Mobil when she heard a short, sharp crack. “I thought it was the machine,” Lima said. But the crack came from the fluid that the machine was pulling: a gooey, black blend of hydrogen and carbon. Instead of stretching, the fluid had fractured. Fractures are known to occur in certain elastic complex fluids, which can act like solids under certain conditions. But Lima was working with a nonelastic simple fluid. Even with almost no elasticity, it snapped apart under stress. “Nobody expected that this would be possible in this kind of simple fluid because viscosity usually just rearranges the molecules,” said Arnold Mathijssen, a fluid physicist at the University of Pennsylvania. “You don’t expect it to crack. But it does, so I think that’s what’s really surprising.” Lima stretched the liquid again and again to prove that the unexpected crack wasn’t a one-off. “Every time that she measured it, the material would break,” said Nicolas J. Alvarez, the professor of chemical engineering at Drexel University whose lab led the research. “It makes a loud pop. I mean, like you just took a rubber band and pulled it and stretched it and it snapped.” Thamires Lima, a research professor in chemical engineering at Drexel University, was stretching a liquid in an extensional rheometer when she heard a short, sharp crack.