Distortion of water droplet surface may increase the likelihood of the droplet freezing

December 12, 2018, US Department of Energy
For 50 years, scientists have struggled with a mystery around how ice nucleates. They lacked an explanation for the efficient ice nucleation that happens when a particle contacts a supercooled water drop. New research addresses this mystery. Credit: Pixabay

Clouds are a big source of uncertainty in computer simulations used to study Earth systems. To reduce that uncertainty, researchers study the formation of ice in clouds. This formation influences precipitation rates, large-scale cloud motions, and cloud optical properties. This research helps to address a long-standing mystery. For more than 50 years, scientists wanted to know why water droplets will freeze at a higher temperature when they are impacted by a particle. It's the pressure of the impact, according to new observations. A new study suggests the warmer freezing point is due to pressure changes resulting from the contact.

In most predictive models of cloud formation and growth, temperature is the most important variable, followed by the material properties of atmospheric particles, in determining whether or not a cloud is composed of water droplets or ice crystals. These new results imply that it may also be important to consider collisions, or dynamic properties, that influence the water surface.

In the atmosphere, droplets of liquid water are frequently found at temperatures below the freezing point of water (0 degrees Celsius) down to temperatures as cold as around minus 40 degrees Celsius. These cold liquid droplets are referred to as "supercooled." Supercooled drops can freeze into in the presence of a class of small particles known as ice-nucleating particles. Understanding which particles serve as ice-nucleating particles under which circumstances and at which temperatures is an active research area because the formation of ice in clouds influences precipitation rate, large-scale cloud motions, and cloud . Much of the ice formation in the atmosphere is a result of catalysis by ice-nucleating particles, and the many different types of ice-nucleating materials are usually characterized by the temperature at which they trigger freezing. A long-standing mystery is the observation that supercooled freeze at a when an ice-nucleating particle impacts the , compared to the same particle being immersed in the droplet. Researchers performed where they held the droplet temperature constant and agitated pure water drops and drops contaminated with a small amount of oil on two different surfaces. The drops were mechanically agitated using a frequency-controlled speaker and photographed with a high-speed camera. With this approach, scientists detected whether freezing occurred and if so, when and where on the drops. These experimental results show that ice nucleation initiated by mechanical agitation is strongly related to the moving and distorted three-phase contact line, suggesting pressure perturbations as a cause.

Explore further: Freezing point of supercooled water varies with electric charge

More information: Fan Yang et al. Nonthermal ice nucleation observed at distorted contact lines of supercooled water drops, Physical Review E (2018). DOI: 10.1103/PhysRevE.97.023103

Related Stories

How ice in clouds is born

November 8, 2017

Something almost magical happens when you put a tray full of sloshing, liquid water into a freezer and it comes out later as a rigid, solid crystal of ice. Chemists at the University of Utah have pulled back the curtain a ...

Cloud research may lead to improved precipitation forecasts

March 18, 2015

From light, airy, and spotless white to threatening and grey-black: Clouds are encountered in various forms. At the AIDA "cloud chamber", scientists of Karlsruhe Institute of Technology (KIT) study how clouds form and which ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

0 comments

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.