Synopsis: Turning Round Drops Square

Researchers can change the shape of a liquid drop by placing it between two stretched elastic films, allowing the drop to be used as a tiny adjustable lens.
Synopsis figure
R. Schulman/McMaster University

A drop of water sitting on a surface minimizes its surface energy by assuming a round shape. Rafael Schulman and Kari Dalnoki-Veress of McMaster University in Canada wondered whether the same would be true for a drop sandwiched between two thin, stretchable films. Would it also form a round blob, or could it take on a wackier shape? In a series of experiments, the duo found that the drop can indeed develop a noncircular outline, such as a square, with its exact shape depending on the amount of tension in the two films. Dalnoki-Veress calls the results “counterintuitive” and “fun,” noting that the experiments were driven purely by curiosity and without any particular application in mind. That said, he imagines potentially using such a stretched and squeezed drop as a tiny lens with adjustable optical properties.

Dalnoki-Veress and Schulman placed a 30- to 300-𝜇m-diameter drop of either glycerol or polyethylene glycol on an elastic film secured to a silicon substrate. They stretched a second elastic film along two orthogonal directions and lowered it over the drop. When the top film’s tension was equal in all directions, the initially round drop flattened into a pancake. When the film’s tension was greater along one direction than along the other, the drop assumed an oval shape. Finally, when they suspended the setup and stretched both the top and bottom films in orthogonal directions, the drop adopted a square outline.

For the suspended drops, the duo monitored the focal properties of the film-drop sandwiches using a laser. They found that flatter drops had longer focal lengths. The focal spot shape also varied, with square drops producing a cross-shaped pattern and oval drops creating a line.

This research is published in Physical Review Letters.

–Christopher Crockett

Christopher Crockett is a freelance writer based in Arlington, Virginia.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Soft MatterFluid Dynamics

Previous Synopsis

Atomic and Molecular Physics

Ripples and Fireworks in Bose-Einstein Condensates

Read More »

Next Synopsis

Interdisciplinary Physics

How Walkers Avoid Collisions

Read More »

Related Articles

Synopsis: Fluid Dynamics Model for Cancer Patterns
Medical Physics

Synopsis: Fluid Dynamics Model for Cancer Patterns

Computer simulations indicate that friction and viscosity determine the patterns that cancerous cells form on skin tissue. Read More »

Synopsis: Air Jets Reduce Car Drag
Fluid Dynamics

Synopsis: Air Jets Reduce Car Drag

Wind tunnel experiments show how blasting air from the back of a vehicle can reshape the vehicle’s wake and lower its drag by several percent. Read More »

Synopsis: Two Nanodrops Zip Together to Form One  
Fluid Dynamics

Synopsis: Two Nanodrops Zip Together to Form One  

Simulations reveal that nanometer-scale droplets merge via a zipping-like action initiated by molecular-sized waves on their surfaces. Read More »

More Articles