Physicists crack science of ice formation

Feb 27, 2013

(Phys.org)—Salt—and just about anything else that dissolves in water, which is called a solute—lowers water's melting point, which is why it's useful for de-icing roads. And the higher the solute concentration, the slower ice forms. That's why solutes, or "cryoprotectants," are added to proteins, cells, tissues and even dead bodies to slow down ice formation during cryopreservation.

Intrigued by this rather poorly understood process, Cornell physicists have discovered that, for a variety of common cryoprotectants, the time for ice to form has a simple exponential variation with concentration. It's the first molecular-level understanding of exactly how solutes slow down ice formation, and it has implications in fields ranging from climate physics to cryopreservation and .

Matthew Warkentin, a physics postdoctoral associate, together with professors of physics Robert Thorne and James Sethna, published these findings online in in January.

Ice forms in supercooled pure water in about 1 microsecond (one-millionth of one second). That time gets multiplied by 10 for every incremental increase in solute concentration. In a 50 percent -water solution, for example, ice formation can take almost a minute.

The simple exponential behavior suggested that there might be a correspondingly simple explanation, Warkentin said.

In order for ice to form, a small cluster of about 50 water molecules must form a crystalline "nucleus"; a smaller cluster will tend to shrink and disappear, but larger clusters will keep growing as long as is available. The researchers postulated that the solute molecules "get in the way" of trying to form a nucleus.

By calculating the probability of finding a nucleus-size volume free of the solute molecules that were preventing nucleation, they derived the exponential dependence on solute concentration and were able to quantitatively replicate data for eight different solutes, ranging from salt to sugar to alcohol. The resulting simple theory used statistical mechanics to extend classical nucleation theory.

In looking at the implications of the work for climate change, for example, Thorne said that modern climate models must take into account a measure of the Earth's reflectiveness, which is influenced by cloud cover. This in turn requires understanding of when and why cloud particles crystallize or remain liquid.

Furthermore, is widely used in medicine and biotechnology, where ice formation can be lethal to cells and tissues. Fertility clinics routinely freeze sperm, eggs and fertilized embryos, and nearly all domestic cattle and swine are propagated using cryopreserved semen, Thorne said.

Aside from its simplicity, an exciting feature of the new theory is that it is generalizable to other liquids and to any system undergoing nucleation, the researchers added.

Explore further: Attosecond laser provides first 'movie' of fast electrons jumping band-gap of semiconductor

add to favorites email to friend print save as pdf

Related Stories

Declining sea ice to lead to cloudier Arctic: study

Mar 31, 2012

Arctic sea ice has been declining over the past several decades as global climate has warmed. In fact, sea ice has declined more quickly than many models predicted, indicating that climate models may not be correctly representing ...

Recommended for you

Unraveling the light of fireflies

11 hours ago

How do fireflies produce those mesmerizing light flashes? Using cutting-edge imaging techniques, scientists from Switzerland and Taiwan have unraveled the firefly's intricate light-producing system for the ...

Where are helium atoms in molecule?

Dec 10, 2014

Frankfurt physicists have once again contributed to resolving a disputed matter of theoretical physics. Science has long since known that, contrary to the old school of thought, helium forms molecules of two, three or even ...

User comments : 0

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.