Synopsis: Bubble bath

The flow properties of foams may not be that different from those of granular materials.
Synopsis figure
Credit: R. Lespiat et al., Phys. Rev. Lett. (2011)

A wet foam—such as that on a cappuccino—and a trough of plastic beads are both made up of nearly spherical, close-packed objects, but do these two types of materials, which are neither fully liquid or solidlike, have anything in common? Experiments presented in Physical Review Letters suggest similarities between foams and granular matter that may lead to a more unified theory for describing the two materials.

A feature of granular materials distinguishing them from liquids is that they jam: the flow is arrested by clusters of grains that can’t reconfigure, like cars merging out of a closed lane. Unlike grains, however, bubbles aren’t hard and slip past each other easily, so it isn’t clear they should behave in a similar way.

Rémi Lespiat and colleagues at the Université Paris-Est, France, have designed a microfluidic chamber to study foams made from nitrogen bubbles in water containing a small amount of surfactant. They let a controlled amount of the bubble mixture rise up onto the bottom surface of a smooth plate, which is bounded on the sides and submerged in the liquid. The plate is tilted up, so buoyancy drives the closely packed gas bubbles upwards along its bottom surface, much as gravity would drive solid grains poured on the top surface downwards.

This setup, with which the team can track the jamming or flow of the bubbles, depending on plate inclination, allows Lespiat et al. to make a direct comparison between grainy matter and foams. – Jessica Thomas


Features

More Features »

Announcements

More Announcements »

Subject Areas

Soft Matter

Previous Synopsis

Particles and Fields

Where are the neutrinos?

Read More »

Next Synopsis

Statistical Physics

Making a hole in a Fermi sea

Read More »

Related Articles

Synopsis: Now You See Them, Now You Don’t
Soft Matter

Synopsis: Now You See Them, Now You Don’t

Whether topological defects form when a disk-shaped particle is placed in a liquid-crystal bath depends on the thickness of the particle. Read More »

Focus: Membrane Holes Can Shrink, Grow, or Stay Put
Soft Matter

Focus: Membrane Holes Can Shrink, Grow, or Stay Put

Pores in a polymer film do not change size over time if they have just the right diameter, according to experiments. Read More »

Viewpoint: Signs of a Gardner Transition in a Granular Glass
Soft Matter

Viewpoint: Signs of a Gardner Transition in a Granular Glass

Two-dimensional disk packings under compression and vibration display signatures of the Gardner phase transition that is thought to occur between the glass and jamming transitions. Read More »

More Articles