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Határfelületi (víz)molekulák
orientációs statisztikája
Horvai György, Jedlovszky Pál, Vincze Árpád, Pártay
Lívia
BME, ELTE, ZMNE
OVERVIEW OF PREVIOUS STUDIES
i.) No particular orientational preferenceCarpenter, Hehre, JPC 94 (1990) 531 hexane
ii.) Dipole of water molecules located
-closest to the apolar phase points toward
the apolar phase
-farther from the apolar phase points toward
the aqueous phasevan Buuren et al., JPC 97 (1993) 9206 decane
iii.) Dipole of water molecules is parallel with
the interfaceLinse, JCP 86 (1987) 417, benzene
Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane
iv.) Dipole of water molecules is almost parallel with the
interface, however, it deviates from parallel alignment
-toward the apolar rather than the aqueous
phase for waters located closest to
the apolar phase
-toward the aqueous rather than the apolar
phase for waters located farther from the
apolar phaseZhang et al., JCP 103 (1995) 10252, octane
Fernandes et al., JPC/B 103 (1999) 6290 2-heptanone
v.) The H-H vector of the water molecules located
closest to the interface is perpendicular
to the interface
Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane
Chang and Dang, JCP 104 (1996) 6772 CCl4
Vincze et al., Anal. Sci. 17 (2001) i317 1,2-dichloroethane
vi.) The H-H vector of the water molecules located farther
from the interface has no particular orientational
preference
Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane
vii.) The H-H vector of the water molecules located farther from
the interface is parallel with the interface
Chang and Dang, JCP 104 (1996) 6772 CCl4
5 10 15 20 25 30 35
-0.002
-0.001
0.000
0.00
0.25
0.50
0.75
1.00
XH
O
H
(X) = w(X) <cos >(X)
(X
)
X/Å
ddd
C B A
0/2
0
systemmass density
(X
)/g
cm-3
Orientation of water at the air/water interface
1. Level of the orientational profiles of various orientational
parameters
Average of parameters describing the orientation of various, molecule-fixed vectors relative to the interface – irrespective the other vectors
Profiles along the interface normal
2. Level of monovariate distributions of the individual orientational
parameters
Distribution of these parameters in separate water layers along the interface normal
3. Level of bivariate distribution of two independent orientational parameters
Joint distribution of two independent orientational parameters in separate water layers along the interface normal. (One to one mapping of orientation on the parameters not
sufficient. Distribution in bulk should be uniform!)
Concept of the bivariate joint distributions
The interfacial orientation of the molecules can be analyzed at different levels of statistics:
Orientációs eloszlási térképek a felszínközeli rétegekben
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
layer C
layer B
layer A
/ d
eg
cos
I
cos
/ d
eg
II
I
/ d
eg
cos
X
I
II
X
III
Dependence of the results on the apolar phase
-1 0 10
30
60
90
/de
g
cos -1 0 1
0
30
60
90
/de
g
cos
-1 0 10
30
60
90
0.5b<(X)<
b(X)<0.1
b
/de
g
cos -1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
/de
gcos
-1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
/de
g
cos
-1 0 10
30
60
90
/de
g
cos -1 0 10
30
60
90
cos /
deg
-1.0 0.0 1.00
30
60
90
cos
/de
g
-1 0 10
30
60
90
0.1b<(X)<0.5
b
water/DCE
water/CCl4
water/benzene
water/n-octane
waterliquid/vapor
layerC
layerB
layerA
/de
g
cos
-1 0 10
30
60
90
/de
g
cos -1 0 10
30
60
90
cos
/de
g
-1 0 10
30
60
90
water/1-octanol
cos
/de
g
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
30
60
90
-1.0 -0.5 0.0 0.5 1.00
20
40
60
80
/ d
eg
cos
I
cos
/ d
eg II
I
/ d
eg
cos
/ d
eg
cos
I
/ d
eg
cos
I
cos
/ d
eg
/ d
eg
cos
I
cos
/ d
eg
I
/ d
eg
cos
/ d
eg
cos
/ d
eg
cos
I
50%
met
han
ol30
% m
eth
anol
20%
met
han
ol10
% m
eth
anol
5% m
eth
anol
0% m
eth
anol
layer Alayer Blayer C
cos
/ d
eg
/ d
eg
cos
cos
/ d
eg
I
cos
/ d
eg
/ d
eg
cos
/ d
eg
cos
I
cos
/ d
eg
Liquid/vapor interface of water-methanol mixtures
WATER ORIENTATION MAPS
Dependence of the results on the aqueous phase
0.00
0.01
0.02
0.03
0.000
0.005
0.010
0.015
0 25 50 75 1000.0
0.2
0.4
0.6
0.8
1.0
water
w(X
)/Å
-3
methanol
m(X
)/Å
-3
0% 30% 5% 50% 10% 90% 20% 100%
mass
X/Å
mas
s(X)/
g cm
-3DENSITY PROFILES DENSITY PROFILES
Non-equilibrium dynamics and structure of interfacial iceOliviero Andreussi, Davide Donadio, Michele Parrinello, Ahmed H. ZewailChemical Physics Letters 2006
Figure 4Orientational probability distribution P(cos θ, φ) for the three regions of three bilayer thick interfacial ice. The two independent orientational parameters (θ, φ) are the angular polar coordinates of the vector normal to the substrate's surface, in a coordinate frame fixed to the individual water molecules [34]. The presence of four preferred orientations is evident for the crystalline systems (below 180 K). At higher temperatures systems present orientational disorder in the bulk region, while molecules at the free surface tend to point towards the inner layers and a more structured bilayer is present at the ice-substrate interface
