Embed Size (px)
Citation preview
© W.F. Kuhs
1
AtmosphericAtmospheric
pressurepressure
icesicesWerner
F.
Kuhs
GZG Abt. Kristallographie, University of Göttingen, Germany
Watsurf, Les Houches, 16 April 2013
Photograph by W.Wisniewski
Ice
Ih
water
biology
© W.F. Kuhs
2
ContentsContents
((molecularmolecular
scalescale
and and nanoscopicnanoscopic))Part I Some personal thoughts about ice Part I Some personal thoughts about ice IhIh
•
The structurestructure
of ice ice IhIh*
and what we can learn from it
•
Hydrogen order order ––
disorderdisorder
and consequences (incl. ice XI)
•
The surfacesurface
of ice Ih
•
Water and guest mobilitiesmobilities
in ice Ih
Part II Some new results on “cubic ice” (“ice Part II Some new results on “cubic ice” (“ice IcIc”)”)•
What has been called “cubic icecubic ice” and implications
•
Discussion !
*
“Ice Ice IhIh
is arguably the most important molecular crystalmost important molecular crystal
in nature, yet our understandingunderstanding
of its structural and dynamical properties is still far from completefar from complete.”
(He et al. 2012 JCP 137: 204505) –
what shall I say….
© W.F. Kuhs
3
Water phase diagramWater phase diagram
© W.F. Kuhs
4
SimilaritySimilarity of of waterwater
and and iceice ??
This conflict has been solved 30 years ago
Corollary: Not every body has taken notice…
© W.F. Kuhs
5
AcknowledgementsAcknowledgementsThis work would not have been possible without the fruitful cooperation with people like
Andrzej
Falenty
John L. Finney
Thomas Hansen
Mogens
Lehmann
Christian Sippel
to name just a few in alphabetic order
Update to Petrenko
& Whitworth (1999) Physics of Ice :Bartels-Rausch et al. (2012) Ice structures, patterns, and processes: A view across the ice fields. Rev.Mod.Physics
84:885-944.
© W.F. Kuhs
6
Water molecules and und HWater molecules and und H--bondsbonds
Free electron pairs of a water molecule Pivot area for two H-bonds
Approximately tetrahedral arrangement of water
molecules
+ +
–
O
This holds up to well over 10 GPa
© W.F. Kuhs
7
HH--bondbond cooperativitycooperativity
cluster
number
of average
length
H-bonded of the
H-bonds
neighbors (ro-o) (Å)
dimer
1 2.91
clusters
containing 6 2.80
20 and 25 water
5 2.82molecules
4 2.81
Ice
Ih
4 2.75
e.g. Ruckenstein
et al. 2007 JPC B 111: 7114Cooperativity
may
be
defined
as occurring
when
the
total effect, for
example,
stabilisation
energy, exceeds
the
simple, additive
sum
of the
individual, isolated effects, e.g., the
interaction
energy
between
two
water
molecules
in the
water
dimer,
making
up the
total (Klein 2006). CooperativityCooperativity
syn. syn. withwith
nonnon--additivityadditivity
The
Average
Pair Interaction Energy
and Length
of Two
H-Bonded
Water Molecule
in a Dimer
and Various
Clusters
Water is a “social” molecule –
it not only lumps together but interacts with its alike to make links even stronger
shortening
© W.F. Kuhs
8
The “ice rules” or BernalThe “ice rules” or Bernal--Fowler rulesFowler rules
•
Every water molecule has 4 neighbours.
•
Between every pair of water molecules is one and only one hydrogen.
•
Otherwise the hydrogen arrangement is statistical.
50%
50%
Ice
Ih
6 possible configurations for each water molecule…
…lead in time- space average to
“half-hydrogen” atoms
© W.F. Kuhs
9
HH--orderedordered and and disordereddisordered
icesices
Ordered
ices: Excellent
reference
data
for
w-w-interactions
Ab-initio
including
vdW
Santra
et al. 2011 PRL 107:185701
DFT Vener
et al. 2010 CPL 500:272-276
Empirical
potentials Vega
et al. 2009 Farad.Disc. 141:251-276
Disordered
ice
Ih: A lot more
of a challenge
An early
attempt
Yoon
et al. 1985 JCP 83:1223-1231
DFT & graph
invariants
Kuo, Klein & Kuhs
2005 JCP 123:134505
MP2 & embed. fragment
He et al. 2012 JCP 141:204505
Do quantum
chemical
calculations
and experiment
agree
?
Ices provide good test cases for quantum chemistry and thus have ever since attracted the “water and biology crowd”
© W.F. Kuhs
10
Proton disorder and consequences Proton disorder and consequences
Oxygen disorder and lateral hydrogen disorder in ice IhDeuteron spin alignment Car-Parinello
MD -
BLYP functional
Fujara, Wefing
& Kuhs
1988 JCP 88:6801 Kuo, Klein & Kuhs
2005 JCP
123:134505
Migrating L-defect
50%
50%
The
ideal…
3° small
angle jump Wrong
!Too
long
!
Experimental
Lateral H disorder Oxygen
disorder
…and the
real system
© W.F. Kuhs
11
Instead of neat geometry: distributions Instead of neat geometry: distributions Kuhs, Finney, Vettier
& Bliss
1984 JCP 81: 3612
Oxygen disorder in ice VIIOrdered ice VIII
H-bond geometry fully establishedLocal H-bond geometry still remains
largely unknown !
Multiple oxygen positions depending on proton configuration
Bad news
at the time as we had set out to establish H-bond geometry for high pressure phases of ice to test water-water
potentials !
Oxygen probility density
function
© W.F. Kuhs
12
Oxygen disorder in ice Oxygen disorder in ice IhIhNeutron diffraction
or perhaps or perhaps
Kuhs
& Lehmann 1985 in Water and Aqueous Solutions ; Proceedings of the Colston
Symposium, Bristol (Eds.GW
Neilson and JE Enderby), Hilger,
Bristol (1986)
p.75-82.
*°
oxygen
Oxygen
displacementsexperimental 0.036 Å
@ 15K Kuhs&Lehmann
1986 Wat.Sci.Rev.
2:1-69 °
ab-initio
0.047 Å
Kuo, Klein & Kuhs
2005 JCP 123:134505
PIMD 0.008 Å
@ 0K
Pamuk
et al. 2012 PRL 108:193003
Shortening
of the
apparent
time-space
averaged
covalent
O-H(D) bond
!exp. H2
O crystallogr. 0.987(5) Å
Kuhs&Lehmann
1986 Wat.Sci.Rev.
2:1-69 °
*
Whalley: I would like to congratulate Dr Kuhs
on a solution to a thirty-year-old problem, when Petersen & Levy (1957) found an anomalous long O-D bond in ice I whereas Kamb
and others measured much shorter ones in ordered phases of ice. This
work shows they are exactly the same.
Thus –
the conflict has been resolved!
°
electronic
(scanned) versions
of Kuhs
& Lehmann 1985,1986 can
be
obtained
from
me
–
send e-mail
© W.F. Kuhs
13
The OThe O--H(D) bond length H(D) bond length
The
covalent
O-H(D) bond
length
for
local
configurations
in ice
Ihexp. H2
O crystallogr. 0.987(5) Å
Kuhs&Lehmann
1986 Wat.Sci.Rev.
2:1-69 °
exp. D2
O pdf 0.985(6) Å
Floriano
et al 1987 Nature 329:821
PI-TIP4P/F MD
0.984
Å
Herrero&Ramirez
2011 JCP 134:094510
MP2 & embed.fr.
0.985(05
) Å
He et al. 2012 JCP 141:204505
Definitely settled –
yet we try to cut down the experimental error bars at present. In any case, O-H in ice Ih
can now be
considered a good test for quantum calculations!
in ice
IhT-dependency
Herrero&Ramirez
2011Herrero&Ramirez
2011
PIMD calcul.
!
°
an electronic
(scanned) version
of Kuhs
& Lehmann 1986 can
be
obtained
from
me
–
send e-mail
© W.F. Kuhs
14
Variation of Variation of HH--bondbond distancesdistances
in in iceice IhIh
From CPMD one obtains -
by averaging over 63 configurations -
a rmsd
< 0.01 Å
Using established bond-lengths – bond-strength relationships one
obtains at
15K
for H2
O: 0.019 Å, D2
O: 0.017Å
as mean deviation
as a consequence of varying local H-bond configurations
Kuhs
& Lehmann 1987 J.Physique
48,C1:3-8 °
Kuhs&Lehmann
1986 Wat.Sci.Rev.
2:1-69
Kuo, Klein & Kuhs
2005 JCP 123:134505
Width
of isolated O-H (D) stretch
Distribution of H-bond
lengths
in ice
Ih
Kuo, Klein & Kuhs
2005 JCP 123:134505
Story not fully settled –
there is room for improvement In any case –
there is variation and it strongly increases with T
°
an electronic
(scanned) version
of Kuhs
& Lehmann 1987 can
be
obtained
from
me
–
send e-mail
© W.F. Kuhs
15
IsotopicIsotopic differencesdifferences
in in iceice IhIh
Method
O-H bondlength
O-D bondlength
Difference
Ice
Ih
@15K diffract.[1] 0.988(4) Å
0.984(3) Å ~ 0.4 %
Water
EPSR [2]
1.005 Å
0.971 Å
~ 3 %
Water isotop.subst. [3]
0.990(5)
0.985(5)
~ 0.5 %
Kuhs
& Lehmann 1987 J.Physique
48,C1:3-8
Disorder
deformation map
of oxygens
atoms
highlighting the
configurational
disorder
[1] Kuhs
& Lehmann 1987 J.Physique
48,C1:3-8, [2]
Soper&Benmore
2008 PRL 101:065502 and 2012 PRL 108:259603, [3]
Zeidler et al. 2011 PRL 107:145501, 2012 PRL 108:259604; 2012 JPCM 24: 284126
NB: The EPSR-based analysis is clearly off the other results. Isotopic differences similar for ice and water and persisting into
the liquid phase –
“structural quantum effects”
H2
O
D2
O
© W.F. Kuhs
16
IceIce IhIh latticelattice
constantsconstantsand their puzzling isotopic differencesRöttger
et al.1994;2012 Acta Cryst
B 50:644; 68:91D2
O has larger LC !
Negative thermal
expansion
Puzzling! Normal isotope effect: V shrinking with increased mass (reduced zero-point motion) and differences getting
smaller at higher temperatures
My hand-waving explanation: Stronger quantum delocalization of the H atoms leads to a stronger (i.e. shorter) H-bond.
© W.F. Kuhs
17
AnomalousAnomalous
nuclearnuclear
quantumquantum
effectseffects
in in iceice
IhIh
Good attempt –
but far from a perfect match Lattice constants are a tough test for quantum chemistry !
Structural quantum effects -
Yet another water anomaly!
Path-integral
MD Pamuk
et al. 2012 PRL:193003
Volume
per molecule
Volume
change
in quasi-harmonic
approx.
Experiment Röttger
et al 1994,2012
Correct
sign
-
but
calculated
differences are
about
one
OoM
larger than
experim.;
volumes
1.3 % smaller
than
experiment
Correct
overall
features
with
vdW-DFPBE
but
increasing
discrepancies
at higher
T
© W.F. Kuhs
18
……and and theirtheir explanationexplanation
Path-integral
MD Pamuk
et al. 2012 PRL:193003
Grüneisen-parameter
V(H2
O) < V(D2
O)
due
to negative γ
of O-H(D) stretch
Negative thermal expansion
< 70K due
to negative γ
of torsional
modes
Negative thermal expansion also observed in other tetrahedral network structures (e.g. Si)
However -
the dominance of stretch over librational
modes seems rather unique to water (“water anomaly”)
© W.F. Kuhs
19
OrderingOrdering iceice
IhIh: : iceice XIXI
Fan et al. 2010 Comp
Mat
Sci
49:S170-S175What is the thermodynamically stable low-T form of ice Ih
?
Popular
antiferroeletric
ordering
Ferroelectric
experimental
evidence
(KOH-doped)
To me -
the case of the equilibrium low-T of ambient pressure ice is not completely closed ! After all –
the HP phase diagram of ice is a
beautiful example that non-equilibrium phases nucleate (ice IV,XII)
Ice
Ih
–
closely
similar
energies
KOH-doping
may
affect
the
ordering
scheme
by
conteracting
the
charge
of ferroelectric domains
(see
Iitaka
(2010). "Stability
of ferroelectric
ice". ArXiv.
arXiv:1007.1792)
© W.F. Kuhs
20
DisorderedDisordered IceIce
(DI) (DI) surfacesurfaceOften called “quasi-liquid-layer” (QLL) –
Nota
bene
-
most often incorrectly
BartelsBartels--Rausch et al. (2012) Rausch et al. (2012) Atmos.Chem.Phys.DiscussAtmos.Chem.Phys.Discuss. 12:30409. 12:30409--3054130541
Difficult to observe –
DI thickness is method-dependent
© W.F. Kuhs
21
DisorderedDisordered iceice
surfacesurfaceGladich
et al. (2011) PCCP 13: 19 960-69
MD-simulationsSazaki
et al. (2012) PNAS 109: 1052-55
interference-contrast
laser
confocal
microscopy
Nanoscopic
phenomena close to Tm
computationally difficult – even with coarse-grained models
Fair enough
–
we
had
seen
this
10 years
ago
–
see
also Shepherd
et al. (2012) JPC C 116This is really exciting –
2 types of „QLL“ !! One more film-like, the other more drop-like
© W.F. Kuhs
22
GoingGoing veryvery
closeclose to Tto Tmm
SazakiSazaki
et al. (2012) PNAS et al. (2012) PNAS 109109: 1052: 1052--5555
within
a few
0.1K from
Tm
two
types
of quasi-liquid-layer
(QLL) appear
α-QLL forms at lower (!) T than β-QLL !!
α- and β-QLL appear to be immiscible liquids !
This is not understood at all !
© W.F. Kuhs
23
-70°C -160°C-100°C -130°C -150°C
1µs
1s
1a
1d
min
How often visits an intrinsic L-Bjerrum defect each water molecule ?
Bjerrum
L-
and D-defects help along rearrangements of H- bonded networks (Wooldridge et al. 1987 JCP 87:4126-31)
Doping can increase the defect concentration (extrinsic defects)
1,E-06
1,E-04
1,E-02
1,E+00
1,E+02
1,E+04
1,E+06
1,E+08
4 5 6 7 8 9
1000/T (K )
τ(s)
IceIce defectsdefects and and waterwater mobilitymobility
OH-
H O3+
L
D
Violating the ice rules !
In undoped
ice
:[L] and [D] >> [OH–] and [H3O+]
© W.F. Kuhs
24
WaterWater mobilitymobility
in in iceice IhIh
Geil et al. (2005) PRB 72:014304 Deuteron-quadrupole-NMR stimulated
echo experiments
The
Bjerrum
D-defect
mediated
reorientations
“fast process”
“slow process”
The long-range H-transport
is of interstitial nature, thus is a transport of intact water molecules. On the average, the molecules traverse 1.5–4 interstitial cavities before they re-adsorb on a regular lattice site.
50 kJ/mol
20 kJ/mol
2 processes: slow (interstitial jumps) and fast (reorientation)
see
also Fujara, Wefing
& Kuhs
(1988) JCP
88:6801-09
© W.F. Kuhs
25
WaterWater mobilitymobility
in in iceice IhIh
Geil et al. (2005) PRB 72:014304
Comparison with dielectric data (open squares).
NMR suggests that the “high- temperature” branch of the Debye
relaxation necessitates interstitial translational jumps
of water
molecules.
Is interstitial diffusion an active source for Bjerrum
defect creation?
Change from one regime to the other at about 220 K
“slow process”
intrinsic
“fast process”
extrinsic defects (impurities)τD = 4 τC
(f)50 kJ/mol
20 kJ/mol
© W.F. Kuhs
26
GuestGuest mobilitymobility
in in iceice IhIh
Ikeda-Fukazawa
et al. (2004) MolSim
30:973-979
“interstitial mechanism” vs. “breaking-bond mechanism”
Migrating of the CO2
molecule from a position between two formerly-occupied lattice O atoms (“B site”), to an adjacent B site by pushing aside H2
O molecules in the ice lattice.
He CO2
interstitial
BBM
Defects in the ice structure promote the diffusion of larger guest molecules
© W.F. Kuhs
27
Johannes Johannes KeplerKepler right and wrongright and wrong
Ice
Ih
Kepler
(1611): Dense packing of dew droplets explain hexagonal shape of snow flakes
The reality of ice Ih: Dense
packing of empty
space
Can be stuffed with H2
, He, Ne
© W.F. Kuhs
28
Part IIPart II““Cubic ice” (“ice Cubic ice” (“ice IIcc
”)* or better “ice ”)* or better “ice IIchch
””
KuhsKuhs, , SippelSippel, , FalentyFalenty
& Hansen (2012) PNAS & Hansen (2012) PNAS 109109:21259:21259--2126421264
see
also Fitzgerald (2013) Physics
Today
66:16
and also our
earlier
papers
on this
matter
Hansen, Koza
& Kuhs
(2008) JPCM 20: 285104 and 285105
*sometimes simply called “crystalline ice” when coming from the amorphous state
© W.F. Kuhs
29
Two possible topologies of Two possible topologies of ambient pressure iceambient pressure ice
Ice Ic ”Cristobalite”
Ice Ih “Tridymite”
cubic hexagonal
Too much of a challenge for computational chemistry !
Both are proton disordered; energy difference ~ 50 J/mol, difference due mainly to longer-ranged dipole-dipole interactions leading to different H-bond angles while distances are the same
“c/a” = 1.633 c/a = 1.628
Different bi-layersIdentical
bi-layers
© W.F. Kuhs
30
The discovery of „cubic ice“The discovery of „cubic ice“König Z.Krist. 105 (1943) 279
Electron
diffraction
Cubic indices
© W.F. Kuhs
31
The ubiquitous nature of ice The ubiquitous nature of ice IIchch
Below ~ 190K good hexagonal ice apparently does not form !!
© W.F. Kuhs
32
CubicCubic iceice in in mesoporesmesoporesAnalysis using a random distribution of growth faults in a 2H structure and “trial and error” fitting
Morishige
& Uematsu
JCP 122 (2005) 044711
In nanoscopic
confinement ice Ich
is stable up to Tm
temperature dependency
size dependency
220 K
© W.F. Kuhs
33
Ice Ice IIchch
from ice IIfrom ice IIKuhs, Bliss
& Finney
(1987) J.Phys.48 C1: 631
Neutron diffraction D1A 1.9 Å
@ ILL
Particle
size
broadening
evaluated
(Scherrer): 160 Å
Stacking-faults explain all features of the pattern !
Neutron diffraction D20 2.4 Å
@ ILL
© W.F. Kuhs
34
StackingsStackings and and iceice IIch ch ((oror IIcc→→hh
))
A
B
C
A
B
A
B
A
B
A
K
K
K
H
H
H
K
H
H
H
K
H
H
K
H
A
B
A
C
A
C
B
C
B
A
B
Topoi
are the mid-points of the H-bonds along stacking axisIce
Ic
or
cubic
ice
(hypothetical)
Ice
Ih
or
hexagonal ice
Stacking-disordered
ice
I or
ice
Ich
© W.F. Kuhs
35
StackingStacking--faultfault--modelmodelReichweite
s=4 model
with
4
parameters
α: HH→K
β: HK→K γ: KH→K
δ: KK→K
pair-probabilities
WHK
= WKH WHH
= WHK
(1-γ)
( )( )( ) ( ) αβδ12αδ1γ1
δ1αWHK +−+−−−
=
δ1W βW HK
KK −=
Hansen, Koza
& Kuhs
(2008) Journal Physics: Cond. Matter 20:285104
Assumption: No dependence
for
the
4th
(and higher) layers.
The structural analysis using diffraction data is non-trivial !
© W.F. Kuhs
36
Cases forCases for reichweitereichweite**α
= β
= γ
= δ
(s
= 2):
The probability of appearance of a particular
type of stacking-sequence is independent on the neighbouring ones and equals its overall proportion.
α
= γ
≠
β
= δ
(s
= 3):
Neighbouring
stacking types affect the probability of appearance of a particular type of stacking-
sequence. α
< δ
implies a preference for repetition
of the previous type of stacking-sequence, while α
> δ
implies a
preference for switching
into the other type, as compared to a random distribution of the two types of stacking-sequences according to the corresponding fractions.
α
≠
γ
or β
≠
δ
(s = 4):
The probability of appearance of a particular type of stacking-sequence is also affected by the next-nearest
stacking-sequences. High values of δ or 1-α enhance the clustering
of cubic or hexagonal stacking-sequences,
respectively. High values of β
and 1–γ
favour consecutive switching, leading to frequently alternating stackings.
*
Reichweite (range
of interaction) as defined
by
Jagodzinski
(1949) Acta Cryst. 2
© W.F. Kuhs
37
““Growing” stacking sequencesGrowing” stacking sequences
Number of replicas used: 500 (all pairs within are analyzed)
Fourier transformation: Structure factor product with 36 interference terms containing probabilities like PAB·BC
(m3
) i.e. the probability of finding a layer BC at a distance m3
from a layer AB etc.
in the
computer
(random
number
0 < r < 1)
α
= 63% β
= 39%
γ
= 35% δ
= 78%
The definite, all-comprising structural model for “cubic ice”
© W.F. Kuhs
38
RietveldRietveld
refinement of stackingrefinement of stacking--faulty icefaulty iceIce
Ich
from
ice
V @ 170K
100hex
111cub/ 002hex
Convincing fit of thousands of patterns
© W.F. Kuhs
39
Fits for various order of Fits for various order of reichweitereichweite ss
s=2 s=3 s=4
Ice Ich
from vapour deposition (frost)
In ice Ich
one needs to consider next-nearest layer
(NOT water molecules) interactions between H and K layers (s=4)
NB: Ice Ic
and ice Ih
is distinguished by the next-nearest water
molecules’ interactions
© W.F. Kuhs
40
Evolution of stacking parametersEvolution of stacking parameters
Clear evidence for the need of going to s=4 !
For s=3 one expects Φc
= α
= γ and 1 –
Φh
= β
= δ
Ice
Ich
isothermal
run
at 175K
© W.F. Kuhs
41
Moore & Moore & MolineroMolinero 20112011
Is
it
cubic? Ice
crystallization
from
deeply
supercooled
water
PCCP 13: 20008-20016
Green: ice
Ih
Red: ice
Ic
Blue: interfacial
ice
whitewhite: amorphous
Malkin
et al. 2012
Simulation time ~ 600 ns, i.e. 2-3 times the crystallization time
K:H ≈ 2:1
K:H ≈ 1:1
© W.F. Kuhs
42
IceIce IIchch
of different of different originorigin
Signatures are fully reproducible
–
This rather hints to structural inheritance
(topotactic
relationships) during the transformation.
Yet -
the underlying mechanisms are not understood at all !
© W.F. Kuhs
43
CubicityCubicity*: isothermal runs (frost)*: isothermal runs (frost)
Ice Ich
is an ever changing entity ! Changes tend towards ice Ih Corollary: Same timescale as for processes in cirrus clouds
Vapour-deposited
ice
* Cubicity
is the fraction of cubic sequences
Ice
Ic→h
© W.F. Kuhs
44
Ostwald‘sOstwald‘s step rulestep rule
∆GA
B
amorphous
ice Ih
ice Ich with increasing
hexagonal components
••
The most disordered material is nucleating firstThe most disordered material is nucleating first••
Along path B the activation Along path B the activation barrier(sbarrier(s) ) is(areis(are) lower) lower
At which temperature do we reach good ice Ih
?
© W.F. Kuhs
45
Something happens in ice at 237Something happens in ice at 237--238K238K
160 180 200 220 240 260 280
0,5
1,0
1,5
2,0
2,5
3,0
Inte
nsity
ratio
I 002 /
I 100
Temperature [K]
Stacking faults in ice Ich
finally disappear and good ice Ih
forms
Kuhs
et al (2004) PCCP 6: 4917-21
Likewise at this T, change of slope of T-dependency of•
NMR spin–lattice relaxation
time T1 for pure ice Ih
•
real part of dielectric permittivities•
frequency of the translational lattice vibrations
as observed by
Raman spectroscopy
Cooperative displacements of water molecules take place on laboratory timescales of seconds to minutes
The intensity ratio of the two
strongest peaks in the
triplet (related to
cubicity)
ice Ich
---
hexagonal
© W.F. Kuhs
46
Particle sizesParticle sizes~ isotropic particles
of ice Ich~ isotropic particles
of ice Ich
Beyond 2000-3000 Å we touch the resolution limit …Ostwald
ripening
leads to decreased particle surface areas
Also confirmed by small angle scattering
on identical samples
Corollary: The isotropy and smallness of the crystals are instrumental for cryo-preservation properties of ice Ich
Ice Ic
from ice V Ice Ic
from ice IX
© W.F. Kuhs
47
Hierarchical structure of frostHierarchical structure of frost
3 µm
300 nm
300 nm
3 µm
300 nm
The smallest units correspond to the crystallites of the diffraction Scherrer
analysis !
A sphere in a sphere in a sphere
Kuhs
et al. (2012) PNAS 109
© W.F. Kuhs
48
Kinky facetingKinky facetingIce Ich
crystals from CO2
-hydrate decomposition @ 167.7-220K
Scalebar
5 μm
Kinks appear also on mature, larger crystals
Corollary: Kinks may alter the surface properties (vapour pressure?), the ice crystal reflectivity and chemical reactivity
© W.F. Kuhs
49
InIn--flight light scattering: rough particlesflight light scattering: rough particles
smooth
rough
Ulanowski
et al. ELS‘XII 2010
In particular cirrus clouds seem to contain ice crystals with rough surfaces. Rough crystals have a two times larger
backscatter!
Is this a signature of facetted ice Ich
crystals?
cirr
usm
ixed
phas
e
modeled< 25 μm
© W.F. Kuhs
50
Cloud Cloud radiativeradiative forcingforcing
The balance between solar albedo
and infrared greenhouse effects
NASA
Cloud albedo
can vary between 10 and 90%
In particular cirrus clouds have fairly unknown back-reflecting (albedo) properties
This is a serious problem for climate research !
?
Model and observation disagree !
© W.F. Kuhs
51
IPCC 2007: IPCC 2007: RadiativeRadiative forcingforcing
Cirrus and Contrails: High impact, low understanding !
© W.F. Kuhs
52
Chemical reactivity on atmospheric iceChemical reactivity on atmospheric iceGao
et al. (2004) Science 303:80-84
Possibly increased chemical reactivity at kinks on crystals planes
Possible that “Δ-ice”
is in fact kinky ice Ich
© W.F. Kuhs
53
DoesDoes truelytruely cubiccubic iceice existexist??
Octahedral
ice
crystal
explaining
Scheiner‘s
halo, Whalley
(1983) JPC 87:4174
Thürmer
& Bartelt
(2008) PR B 77:195425
Growth around a screw dislocation
may yield fairly pure
cubic stackings
(bilayers
colour-coded)
The question remains open –
yet to me it seems likely that bulk pure ice Ic
does not
exist !
Other explanations for this halo exist !
ice Ic
ice Ih
© W.F. Kuhs
54
ThankThank youyou
! ! DiscussionDiscussion pleaseplease
!!
