Synopsis: Drops Act Like Tension “Compasses”

A liquid drop’s shape can be used to detect tension anisotropies in an underlying elastic membrane.
Synopsis figure
R. Schulman et al., Phys. Rev. Lett. (2017)

Want to know the tension in a stretched membrane or thin film? Spraying it with liquid droplets might give you the answer. Rafael Schulman from McMaster University, Canada, and colleagues have shown that otherwise spherical drops resemble ellipses when they are sprayed on a film in which the tension is greater in one direction than in the other. The finding suggests that droplets could map the tension in a film much like iron filings trace the field from a magnet.

The group suspended an elastic polymer film such that it had a uniform tension and then sprayed the film with glycerol drops. Imaging from above, they observed that the drops assumed near-perfect circular shapes. But when the team stretched the film to induce an anisotropic tension, drops that were subsequently sprayed onto the surface looked more like peanut M&M’s—fatter along one axis than the other. Specifically, each drop’s long axis was lined up with the direction in which the film had been most strained, that is, the direction of higher tension.

Based on a side view of the drop-film profile, Schulman’s group and his colleagues at the ESPCI Paris were able to calculate the local tension in the film using an existing model, which they modified to incorporate anisotropic tension. This enabled them to map both the direction and magnitude of stresses at each point in the film. And unlike other tension-measurement approaches, theirs left the film intact.

This research is published in Physical Review Letters.

–Katherine Wright

Katherine Wright is a Contributing Editor for Physics.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Fluid DynamicsSoft Matter

Previous Synopsis

Soft Matter

Sandy Scaling Law

Read More »

Next Synopsis

Astrophysics

Blocking out Starlight

Read More »

Related Articles

Viewpoint: Jamming Grains Come Full Circle
Soft Matter

Viewpoint: Jamming Grains Come Full Circle

The characterization of a new transition in sheared grains helps to fill in the phase diagram for granular materials. Read More »

Focus: Leaf-Like Veins Are Key to Efficient Pump
Fluid Dynamics

Focus: Leaf-Like Veins Are Key to Efficient Pump

A network of “veins” improves performance for a leaf-mimicking pump that could be used in microfluidics devices. Read More »

Synopsis: Softening Tones Make Shear-Thickening Fluids Relax
Materials Science

Synopsis: Softening Tones Make Shear-Thickening Fluids Relax

An acoustic signal can control the viscosity in shear-thickening materials, which have potential uses as impact absorbers. Read More »

More Articles