Limits...
Anomalous Behavior of the Homogeneous Ice Nucleation Rate in "No-Man's Land".

Laksmono H, McQueen TA, Sellberg JA, Loh ND, Huang C, Schlesinger D, Sierra RG, Hampton CY, Nordlund D, Beye M, Martin AV, Barty A, Seibert MM, Messerschmidt M, Williams GJ, Boutet S, Amann-Winkel K, Loerting T, Pettersson LG, Bogan MJ, Nilsson A - J Phys Chem Lett (2015)

Bottom Line: We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit T H by cooling micrometer-sized droplets (microdroplets) evaporatively at 10(3)-10(4) 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 10(6)-10(7) K/s.

View Article: PubMed Central - PubMed

Affiliation: PULSE Institute, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.

ABSTRACT

We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit T H by cooling micrometer-sized droplets (microdroplets) evaporatively at 10(3)-10(4) 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 10(6)-10(7) 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.

No MeSH data available.


Related in: MedlinePlus

Droplet temperature asa function of travel time (or distance traveled)in vacuum for water microdroplets with diameters of 9 μm (brownsolid line) and 12 μm (red solid line). The temperature wasobtained using the Knudsen theory of evaporation.39 The ice ratio (fice) (dashedline) increased rapidly as the 9 and 12 μm droplets’travel time in vacuum increased beyond 2 and 4 ms, respectively. Theerror bars in fice are the standard deviationof individual recordings at each distance, to account for hit ratevariations, and droplet trajectory jitters due to jet breakup anddroplet freezing.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4507474&req=5

fig1: Droplet temperature asa function of travel time (or distance traveled)in vacuum for water microdroplets with diameters of 9 μm (brownsolid line) and 12 μm (red solid line). The temperature wasobtained using the Knudsen theory of evaporation.39 The ice ratio (fice) (dashedline) increased rapidly as the 9 and 12 μm droplets’travel time in vacuum increased beyond 2 and 4 ms, respectively. Theerror bars in fice are the standard deviationof individual recordings at each distance, to account for hit ratevariations, and droplet trajectory jitters due to jet breakup anddroplet freezing.

Mentions: The experiments were conducted using a gas dynamic virtualnozzle(GDVN)45 to generate, in vacuum, a trainof microdroplets with uniform diameter of 9 or 12 μm that aresubsequently probed by X-rays. The droplets cool evaporatively, decreasingtheir temperature as they travel farther from the nozzle and spendlonger time in vacuum. This results in cooling rates of 103–104 K/s around TH priorto crystallization. Hard X-ray laser pulses, each ∼50 fs induration, from LCLS were used to probe the structure of individualdroplets at various distances from the nozzle exit, hence varyingthe droplet temperature. The scattering patterns from individual dropletshit by the X-ray pulse were recorded over an estimated temperaturerange of 227–252 K (Figure 1) and sorted according to whether they consisted ofonly diffuse rings indicating scattering from pure liquid water orcontained intense and discrete Bragg reflections that indicate diffractionfrom ice crystals.39 We collected at least1800 individual scattering patterns at each distance or temperature.As the droplets spend more time in vacuum and evaporatively cool,the fraction of ice-containing shots (fice) remains near zero for about 1.2 and 3 ms travel time for the 9and 12 μm droplets, respectively (Figure 1). This fraction increases rapidly to 0.2in the next 1 ms for both droplet sizes and to 0.97 in the next 2ms for 12 μm droplets. The error bars in fice represent the standard deviation of individual recordingscollected at each distance and include variations in the hit rateand droplet trajectory jitters. The droplet trajectory jitter is expectedto arise from jet breakup to form droplets and from the freezing processof the droplets. The onset temperatures where ice is first detectedon these time scales are 232 and 230 K for the 9 and 12 μm droplets,respectively. We use fice to estimate J assuming, as in other nucleation rate studies,19−21,46−49 that the nucleation rate followsPoisson statistics and the observed Bragg reflections expected fromice in each shot originate from single nuclei (see Experimental Section). Here, we obtain ice nucleation ratesranging from 2.1 × 1011 to 3.6 × 1012 cm–3s–1 as the temperature decreasesfrom 232 to 227 K (Figure 2a,b). The error bars on the nucleation rate (Figure 2a) account for the standarddeviation in fice and the uncertaintyin how many ice nuclei exist in each droplet that shows Bragg reflections(see Experimental Section).


Anomalous Behavior of the Homogeneous Ice Nucleation Rate in "No-Man's Land".

Laksmono H, McQueen TA, Sellberg JA, Loh ND, Huang C, Schlesinger D, Sierra RG, Hampton CY, Nordlund D, Beye M, Martin AV, Barty A, Seibert MM, Messerschmidt M, Williams GJ, Boutet S, Amann-Winkel K, Loerting T, Pettersson LG, Bogan MJ, Nilsson A - J Phys Chem Lett (2015)

Droplet temperature asa function of travel time (or distance traveled)in vacuum for water microdroplets with diameters of 9 μm (brownsolid line) and 12 μm (red solid line). The temperature wasobtained using the Knudsen theory of evaporation.39 The ice ratio (fice) (dashedline) increased rapidly as the 9 and 12 μm droplets’travel time in vacuum increased beyond 2 and 4 ms, respectively. Theerror bars in fice are the standard deviationof individual recordings at each distance, to account for hit ratevariations, and droplet trajectory jitters due to jet breakup anddroplet freezing.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507474&req=5

fig1: Droplet temperature asa function of travel time (or distance traveled)in vacuum for water microdroplets with diameters of 9 μm (brownsolid line) and 12 μm (red solid line). The temperature wasobtained using the Knudsen theory of evaporation.39 The ice ratio (fice) (dashedline) increased rapidly as the 9 and 12 μm droplets’travel time in vacuum increased beyond 2 and 4 ms, respectively. Theerror bars in fice are the standard deviationof individual recordings at each distance, to account for hit ratevariations, and droplet trajectory jitters due to jet breakup anddroplet freezing.
Mentions: The experiments were conducted using a gas dynamic virtualnozzle(GDVN)45 to generate, in vacuum, a trainof microdroplets with uniform diameter of 9 or 12 μm that aresubsequently probed by X-rays. The droplets cool evaporatively, decreasingtheir temperature as they travel farther from the nozzle and spendlonger time in vacuum. This results in cooling rates of 103–104 K/s around TH priorto crystallization. Hard X-ray laser pulses, each ∼50 fs induration, from LCLS were used to probe the structure of individualdroplets at various distances from the nozzle exit, hence varyingthe droplet temperature. The scattering patterns from individual dropletshit by the X-ray pulse were recorded over an estimated temperaturerange of 227–252 K (Figure 1) and sorted according to whether they consisted ofonly diffuse rings indicating scattering from pure liquid water orcontained intense and discrete Bragg reflections that indicate diffractionfrom ice crystals.39 We collected at least1800 individual scattering patterns at each distance or temperature.As the droplets spend more time in vacuum and evaporatively cool,the fraction of ice-containing shots (fice) remains near zero for about 1.2 and 3 ms travel time for the 9and 12 μm droplets, respectively (Figure 1). This fraction increases rapidly to 0.2in the next 1 ms for both droplet sizes and to 0.97 in the next 2ms for 12 μm droplets. The error bars in fice represent the standard deviation of individual recordingscollected at each distance and include variations in the hit rateand droplet trajectory jitters. The droplet trajectory jitter is expectedto arise from jet breakup to form droplets and from the freezing processof the droplets. The onset temperatures where ice is first detectedon these time scales are 232 and 230 K for the 9 and 12 μm droplets,respectively. We use fice to estimate J assuming, as in other nucleation rate studies,19−21,46−49 that the nucleation rate followsPoisson statistics and the observed Bragg reflections expected fromice in each shot originate from single nuclei (see Experimental Section). Here, we obtain ice nucleation ratesranging from 2.1 × 1011 to 3.6 × 1012 cm–3s–1 as the temperature decreasesfrom 232 to 227 K (Figure 2a,b). The error bars on the nucleation rate (Figure 2a) account for the standarddeviation in fice and the uncertaintyin how many ice nuclei exist in each droplet that shows Bragg reflections(see Experimental Section).

Bottom Line: We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit T H by cooling micrometer-sized droplets (microdroplets) evaporatively at 10(3)-10(4) 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 10(6)-10(7) K/s.

View Article: PubMed Central - PubMed

Affiliation: PULSE Institute, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.

ABSTRACT

We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit T H by cooling micrometer-sized droplets (microdroplets) evaporatively at 10(3)-10(4) 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 10(6)-10(7) 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.

No MeSH data available.


Related in: MedlinePlus