Explaining the shape of freezing droplets

August 4, 2014
This image shows the freezing front, resulting in a pointy shape.

A water droplet deposited onto an icecold surface clearly has more effect than a drop in the ocean: the droplet will freeze in a peculiar way, forming a pointy tip. Scientists of the University of Twente have, in cooperation with colleagues from Paris, Brussels and Munich, found an explanation for this remarkable shape. They used video images and advanced mathematics for this. Insight into this process is also useful for understanding processes like 3D printing. The results are published in the August 1 issue of Physical Review Letters.

It is typically a 'do try this at home' experiment that can be performed using a deep-frozen plate (colder than minus 15 degrees Celsius, preferably) and some water at room temperature. A droplet falling on the plate, will freeze starting at the bottom. It will not stay round, but turn into a conical shape. Existing theories could not explain this shape transformation. In their latest publication, the scientists from the University of Twente now present an explanation. Using their theory, the cone angle can also be calculated. These new insights provide useful information for e.g. icing processes on aircraft wings or for manufacturing technologies like 3D printing, where molten metal drops solidify when hitting a surface.

Looking inside a droplet, to investigate the freezing process, is quite complicated. The droplet acts as a lens and distorts the 3D image. That's why the researchers found a way to get from a 'flat', 2D droplet. Between two closely spaced glass plates, a droplet is released onto the cold surface. The freezing process can then be monitored very well. The video images prove that the freezing front always has a 90 degrees angle with the water surface. The consequence is that the front turns from spherical to concave. As ice takes about 10 percent more volume than water, in the end ice finds a 'way out' via a pointy tip. Calculations show that this cone angle is always circa 140 degrees, indepent of drop temperature or size.

This research has been done by Oscar Enríquez and Jacco Snoeijer of the University of Twente, The Netherlands, together with colleagues from the Universität der Bundeswehr in Munich, the Laboratoire Matière et Systemes Complexes in Paris and the Université Libre in Brussels.

Explore further: Freezing water droplets form sharp ice peaks

More information: 'Universality of Tip Singularity Formation in Freezing Water Drops', Physical Review Letters 113, August 1, 2014. DOI: 10.1103/PhysRevLett.113.054301

Related Stories

When liquids behave like solids

December 10, 2013

(Phys.org) —When a rubber ball and a droplet of water are compressed onto a solid surface, they behave very differently. For the ball, the compression process is reversible, so the ball retains its original form when decompressed. ...

How do our cells move? Liquid droplets could explain

May 1, 2014

Living cells move; not just bacteria, but also cells in our own bodies. EPFL scientists have discovered a new relationship between the three-dimensional shape of the cell and its ability to migrate. The work has important ...

Basic science in evaporating droplets

April 18, 2013

What happens if you slowly evaporate a droplet containing dissolved particles? The question sounds simple, but it involves a surprising amount of basic physics and mathematics. Hanneke Gelderblom of the University of Twente ...

Unexpected ice-formation mechanism

January 18, 2012

(PhysOrg.com) -- Extremely hydrophobic materials cause water to roll right off objects that have been coated with them. Up to now, it was assumed that aircraft or wind turbines coated in such a way did not ice up as easily. ...

Droplets that Roll Uphill

September 24, 2007

A recent experiment conducted by physicists at University of Bristol in the United Kingdom has shown that liquid drops can defy gravity. Droplets of liquid on an inclined plate that is shaken up and down can travel uphill ...

Recommended for you

Electromagnetic water cloak eliminates drag and wake

December 11, 2017

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while simultaneously helping it avoid detection.

Three kinds of information from a single X-ray measurement

December 11, 2017

Whatever the size of mobile phones or computers are, the way in which such electronic devices operate relies on the interactions between materials. For this reason, engineers as well as researchers need to know exactly how ...

New manifestation of magnetic monopoles discovered

December 8, 2017

The startling similarity between the physical laws describing electric phenomena and those describing magnetic phenomena has been known since the 19th century. However, one piece that would make the two perfectly symmetric ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.