title: Two types of quasi-liquid layers on ice crystals are formed kinetically.
abstract: Surfaces of ice are covered with thin liquid water layers, called quasi-liquid layers (QLLs), even below their melting point (0 °C), which govern a wide variety of phenomena in nature. We recently found that two types of QLL phases appear that exhibit different morphologies (droplets and thin layers) [Sazaki G. et al. (2012) Proc Natl Acad Sci USA 109(4):1052-1055]. However, revealing the thermodynamic stabilities of QLLs remains a longstanding elusive problem. Here we show that both types of QLLs are metastable phases that appear only if the water vapor pressure is higher than a certain critical supersaturation. We directly visualized the QLLs on ice crystal surfaces by advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on ice crystal surfaces. At a certain fixed temperature, as the water vapor pressure decreased, thin-layer QLLs first disappeared, and then droplet QLLs vanished next, although elementary steps of ice crystals were still growing. These results clearly demonstrate that both types of QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. To our knowledge, this is the first experimental evidence that supersaturation of water vapor plays a crucially important role in the formation of QLLs.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Harutoshi
authors.initials: H
authors.lastname: Asakawa
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan sazaki@lowtem.hokudai.ac.jp.
authors.forename: Gen
authors.initials: G
authors.lastname: Sazaki
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Nagashima
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Nakatsubo
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Furukawa
keywords: advanced optical microscopy; metastable phase; molecular-level observation; supersaturation
references.citation: Sci Am. 2000 Feb;282(2):50-3
references.pmid: 10710786
references.citation: Proc Natl Acad Sci U S A. 2010 Nov 16;107(46):19702-7
references.pmid: 20974928
references.citation: Phys Rev B Condens Matter. 1986 Dec 1;34(11):7506-7516
references.pmid: 9939429
references.citation: Phys Rev Lett. 2001 Feb 19;86(8):1554-7
references.pmid: 11290191
references.citation: Proc Natl Acad Sci U S A. 2012 Jan 24;109(4):1052-5
references.pmid: 22232653
references.citation: Science. 1989 Dec 22;246(4937):1591-3
references.pmid: 17834424
references.citation: Phys Rev Lett. 1987 Dec 7;59(23):2678-2681
references.pmid: 10035620