How tiny droplets can deform ice: Findings show potential for cryopreservation and food engineering

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When water freezes slowly, the location where water turns into ice—known as the freezing front—forms a straight line. Researchers from the University of Twente showed how droplets that interact with such a freezing front cause surprising deformations of this front. These new insights were published in Physical Review Letters and show potential for applications in cryopreservation and food engineering techniques.

When water freezes, it is often thought of as a predictable, solid block forming layer by layer. But what happens if the progressing freezing front encounters tiny particles or droplets? Researchers from the University of Twente have explored this question, discovering that droplets can cause surprising deformations in the way ice forms.

Droplets deform ice

In their new study published in Physical Review Letters, scientists in the Physics of Fluids group observed that droplets can alter the behavior of a freezing front. Scientists have long known that solid particles, like dust, deform the freezing front based on the difference between how well the particles and water conduct heat. However, when droplets meet the freezing front, they can cause a deformation of the front in ways that were previously unknown and are fundamentally different from the way in which particles deform the front.

The team found that the interaction between the freezing front and a droplet involves complex forces known as thermal Marangoni forces. In simple terms, the surface tension of the droplet depends on temperature.

As the freezing front approaches the droplet, the temperature on one side of the droplet is different than on the other side. That causes a difference in surface tension, which manifests as a force. This force, the thermal Marangoni force, causes a flow inside and outside the droplet. The flow outside the droplet moves warmer water towards the front, which causes the ice to bend away from the droplet.

Possible applications

This finding opens new doors for understanding processes where the freezing of droplets is a factor, such as in cryopreservation and food engineering. UT researcher Detlef Lohse explains, "Our findings can help us control whether particles become part of a material or are pushed away as it solidifies."

By understanding these flow dynamics, scientists will be able to improve methods that require precise freezing control, ultimately harnessing this behavior for more efficient materials and processes.

More information: Duco van Buuren et al, Deforming Ice with Drops, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.214002

Provided by University of Twente