Synopsis: Cracks in the Cornstarch

When rapidly deformed, a suspension of cornstarch in water not only becomes stiff like a solid but also fractures like one.
Synopsis figure
M. Roché et al., Phys. Rev. Lett. (2013)

Collections of particles, whether dry or suspended in liquid, can act like either fluids or solids under different conditions. A household example is a mixture of cornstarch and water, which normally flows slowly like a viscous liquid but when rapidly shocked can be solid enough to hold a person’s weight (for a second or two). In Physical Review Letters, Matthieu Roché and colleagues at Princeton University, New Jersey, characterize how this stiff material then cracks, if the stress is high enough.

On impact, the stiffening of a rapidly deformed suspension reflects “jamming”: the liquid is expelled, but the cornstarch particles (typically microns in size) are pushed against each other before they can get out of the way, so they form a rigid framework. The team used high-speed photography to monitor a thin layer of the suspension as they dropped a cylindrical rod end-on onto the layer from various heights. The impact creates a solid ring a few millimeters thick—visible because it is less glossy than the initial suspension—and then a gap opens around the cylinder. If the layer is thin enough, though, cracks rapidly shoot out radially from the edge of this hole, propagating further in thinner layers. The cracks then heal as water flows back into the solidified region. Roché et al.’s careful measurements under various conditions let the researchers calculate the mechanical strength of the short-lived solid, as well as the kinetic energy required to cause crack propagation. The counterintuitive behavior could shed light on other important liquid-particle mixtures ranging from foodstuffs to earthquake-jostled ground. – Don Monroe


More Announcements »

Subject Areas

Soft Matter

Previous Synopsis

Biological Physics

The Hairs Rustling in Your Ears

Read More »

Next Synopsis

Nuclear Physics

Squashed Nuclei

Read More »

Related Articles

Focus: Complex Crystals Form from Heterogeneous Particles
Materials Science

Focus: Complex Crystals Form from Heterogeneous Particles

A suspension containing particles with wide-ranging diameters can crystallize into multiple ordered structures. Read More »

Viewpoint: Particles Move to the Beat of a Microfluidic Drum
Fluid Dynamics

Viewpoint: Particles Move to the Beat of a Microfluidic Drum

A thin vibrating plate can organize microscopic particles within a liquid into different patterns, an effect like that observed in 18th century studies of musical instruments. Read More »

Viewpoint: Turning Down the Volume on Granular Materials
Statistical Physics

Viewpoint: Turning Down the Volume on Granular Materials

A reformulation of the statistical mechanics of granular materials replaces the volume of the material with a function related to its structure. Read More »

More Articles