A Simple Liquid Can Shatter Like Glass
Scientists thought only springy, elastic fluids could fracture. This one popped like a snapped rubber band.
Quanta Magazine · We Know Simple Fluids Can Flow. Turns Out, Some Can Fracture.Under a hard enough pull, a plain liquid with almost no springiness can snap like glass. The fluid was an oil-like black goo made of hydrogen and carbon, with almost no elasticity, the springiness that lets a material store stress and bounce back.
Research professor Thamires Lima stretched it again and again, and Nicolas J. Alvarez, the Drexel University chemical engineering professor whose lab led the research, said it broke every time with a loud pop, like a snapped rubber band. When the team looked closer with high-speed cameras, they concluded the split matched the shattering seen in dropped dishware.
That overturned an assumption. Nicolas Alvarez's Drexel lab had shown in 2016 that melted polystyrene, a complex fluid full of long, tangled molecular chains, could crack like a solid, and the team had thought elasticity was a prerequisite for liquids to break. “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.
Alvarez suggests the limit may depend not on elasticity, but on the more fundamental cohesive energy that holds a liquid’s molecules together.
Questions people ask
What is the difference between a simple fluid and a complex fluid?
A simple fluid is made of small molecules that slide past one another and do not store much stress, like oil or honey. A complex fluid contains structures such as long, entangled polymer chains that give it some elasticity, so it can briefly act solid and bounce back.
Why did scientists already know that melted polystyrene could fracture?
Melted polystyrene is plastic heated until it flows. Its long molecular chains get tangled like cooked spaghetti, giving the melt elasticity. That elasticity was why scientists previously believed it could crack like a solid.
Could water or honey shatter in my kitchen?
Not under ordinary conditions. The fracturing happened during a fast, forceful stretch in a specialized instrument. Everyday pouring or stirring is far too gentle to make water or honey snap.