Slipping on ice may be down to too much alcohol (or salt)…
10 Dec 2023
It’s a challenge for pedestrians and road users but also a major problem for industry: why are some ice deposits more slippery than others?
The answer may not have been clear to scientists, says a report from the University of Illinois Chicago, because labs have tended to test ice made from pure water.
In the outside world, however, ice tends to contain an appreciable number of commonplace contaminants – such as salt, soap and alcohol. And these impact the stickiness of the ice itself.
“Be it dirty sidewalks or the hull of Arctic-going marine ships, there’s always impurities there. So, the natural question that comes to mind is: What is the influence of these compounds on how strongly ice sticks to surfaces?” said senior author associate professor of mechanical and industrial engineering at UIC Sushant Anand.
His research team prepared ice with various kinds and quantities of contaminants to see how strongly they adhered to various industrial materials. Under certain conditions, impure ice proved far less sticky.
This was influenced by factors that included the way the water freezes when it contains impurities but also the specific structure where ice touches a solid material, termed the quasi-liquid layer.
“The ice region near a solid has liquid-like properties, and its thickness could contribute to how tightly ice sticks,” Anand explained.
To better study the layer, Anand secured the collaboration of his colleague Subramanian Sankaranarayanan and co-workers at the UIC/Argonne National Laboratory. Their work identified that during the freezing process, impure water will expel contaminants to form a more slippery liquid layer.
“These insights could lead to the design of next-generation winterization techniques that slowly release contaminants to promote facile ice shedding,” said the paper’s first author, PhD Rukmava Chatterjee.
However, vessels in polar climates frequently struggle through ice, despite the fact that sea water contains high salt content that ought to make for less adhesive ice. Further experimentation revealed that the rate of freezing was also a factor.
This showed that a slow freezing process creates pockets of concentrated contaminants or expels them altogether, leaving the ice stronger; weaker adhesion required a faster freezing process.
Said Anand: “Our study represents just the tip of the iceberg, opening new lines of investigation of how impure ice adheres with widespread implications across multiple disciplines,” Anand said.
Pic: IBCSO S.Ocean mapping (Wegener Institute/ S Hendricks)