Abstract
We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit TH by cooling micrometer-sized droplets (microdroplets) evaporatively at 103–104 K/s and probing the structure ultrafast using femtosecond pulses from the Linac Coherent Light Source (LCLS) free-electron X-ray laser. Below 232 K, we observed a slower nucleation rate increase with decreasing temperature than anticipated from previous measurements, which we suggest is due to the rapid decrease in water’s diffusivity. This is consistent with earlier findings that microdroplets do not crystallize at <227 K, but vitrify at cooling rates of 106–107 K/s. We also hypothesize that the slower increase in the nucleation rate is connected with the proposed “fragile-to-strong” transition anomaly in water.
Highlights
We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit TH by cooling micrometer-sized droplets evaporatively at 103−104 K/s and probing the structure ultrafast using femtosecond pulses from the Linac Coherent Light Source (LCLS) free-electron X-ray laser
U nderstanding the phase transition from supercooled water or amorphous ice to crystalline ice is key to various fields ranging from cryobiology to atmospheric and astrophysical sciences.[1−5] Accurate determination of ice nucleation kinetics and the involved structural transformation is essential for modeling atmospheric cloud formation and the corresponding thermostatting effects on the world climate
The lack of direct measurements of the nucleation rate, the diffusivity and the solid−liquid water interfacial free energy limits our knowledge on ice nucleation kinetics within this important region of the water phase diagram
Summary
Letter cooling rates (from ∼1 K/min to ∼100 K/s) and to where amorphous ice crystallizes upon heating.[1,8,11] the temperature region below TH and above TX is referred to as “no-man’s land”. There have been several attempts to circumvent the limitation set by TH to achieve deeper supercooling and observe homogeneous ice nucleation events in “no-man’s land” This is often done by increasing the sample cooling rate and reducing the sample dimensions to nanometer sizes that effectively decreases the nucleation probability.[19−21] reducing the sample volume to such small dimensions dramatically increases the surface-to-volume ratio and the sample internal pressure due to the reduced radius of curvature (described by the Young−Laplace equation). The onset temperatures where ice is first detected on these time scales are 232 and 230 K for the 9 and 12 μm assuming, as idnroopthleetrs,nurecslepaetciotinverlayt.eWstueduiesse,19f−ic2e1,t4o6−e49sttimhaattetheJ nucleation rate follows Poisson statistics and the observed
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