G Dlubek 1 Yang Yu 2 R KrauseRehberg 2 W Beichel 3 and I Krossing 3 1 ITA Institut für Innovative Technologien Köthen Germany 2 MartinLutherUniversität Halle Institut für Physik 06099 HalleSaale Germany ID: 459092
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Slide1
Investigation of Ionic Liquids by Positron Annihilation Lifetime Spectroscopy
G. Dlubek
1†
, Yang. Yu2, R. Krause-Rehberg2, W. Beichel3 and I. Krossing3 1 ITA Institut für Innovative Technologien, Köthen, Germany2 Martin-Luther-Universität Halle, Institut für Physik, 06099 Halle(Saale) Germany3 Institut für Anorganische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, D-79104 Freiburg i. Br., Germany
Sep. 5th. 2011Slide2
Outline
Free volume influence to molecular transport property
F
ürth theory
Ionic Liquids
Experiment results and discussion
ConclusionSlide3
Permeation
properties (small molecules in polymer), viscosity, viscoelasticity, glass transition, volume recovery, mechanical propertiesFluidity: Doolittle:
Mobility: Cohen-Turnbull Equation:Permeability coefficient
:Selectivity:Ionic conductivity:
Free volume influence to molecular transport propertySlide4
Fürth’s hole theory
: The energy required for the formation of a hole of spherical shape of radius r in a continuum is equal to the sum of the work to be done against the surface tension and the work to be done against the pressure.
Relation between hole volume and surface tension.
T
s
P
Ref:
Dlubek
, G.,
Yu, Yang, et
al.,
Free volume in
imidazolium
triflimide
([C
3
MIM][NTf
2
]) ionic liquid from positron lifetime: Amorphous, crystalline, and liquid states.
The Journal of Chemical Physics, 2010.
133
(12): p. 124502-10
.
[
Fürth
, R. Mathematical Proceedings of the Cambridge Philosophical Society, 1941.]Slide5
Ionic Liquids (ILs):
Definition: organic salts with melting points below 100 oC or even room temperature(RTILs).Structure: organic cations
paired with organic or inorganic anions.
[
OTf
]
-
[PF
6
]
-
[
Cl
]
-
[B(
hfip
)
4
]
-
Ionic formulae of the ionic liquids studied in this work.
[BMIM]
+
[BF
4
]
-
[NTf
2
]
-Slide6
Experiment results and discussion
The mean, <
3
>, and the standard deviation,
3
,
of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][BF
4
]
.
T
g
indicates the glass transition temperature and
T
k
the “knee” temperature
.
The intensity
I
3
of the
o
-Ps lifetime as a function of temperature
T
during cooling and heating of [BMIM][BF
4
].
[BMIM][BF
4
]: Slide7
Number-weighted mean <
v
h
> (spheres) and standard deviation sh (squares) of the hole size calculated from positron lifetime.[BMIM][BF4]:
Plot of the specific volume from PVT experiment under 0
MPa
vs
the mean hole volume at
supercooled
liquid state (between
T
g
and
T
k
). The line is a linear fit of the data.
N
h
’ = 0.442
10
21
g
-1
;
V
occ
= 0.7574 cm
3
/g.
Slide8
[BMIM][NTf2]:
The mean, <
3
> (squares), and the standard deviation,
3
(spheres), of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][NTf
2
]
.
The
o
-Ps intensity
I
3
as a function of temperature during cooling and heating of [BMIM][NTf
2
]Slide9
[BMIM][NTf2]:
Plot of the specific volume from PVT experiment under 0
MPa
vs
the mean hole volume at
supercooled
liquid state (between
T
g
and
T
k
). The line is a linear fit of the data.
N
h
’ = 0.179
x
10
21
g
-1
V
occ
= 0.6405 cm3/g. Slide10
[BMIM][OTf
]:
The mean, <
3
>,
and the standard deviation,
3
,
of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][
OTf
].
T
cr
and
T
m
show the temperatures of crystallization (during cooling) and melting.
The
o
-Ps intensity
I
3
.Slide11
The mean, <
3
>, and the standard deviation
,
3
,
of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][PF
6
]
.
4
shows an additional
o
-Ps lifetime, which appears after transformation of the
cr
-II into the
cr
-I phase.
[BMIM][PF
6
]:The two
o
-Ps intensities
I
3
and
I
4
.Slide12
Plot of the specific volume from PVT experiment under 0
MPa
vs
the mean hole volume at
supercooled
liquid state. The line is a linear fit of the data.
N
h
’ = 0.376
x
10
21
g
-1
V
occ
= 0.6670
cm
3
/g.
[BMIM][PF6
]:Slide13
The mean, <
3
>,
and the standard deviation
,
3
,
of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][
Cl
].
4
shows an additional
o
-Ps lifetime which appears after crystallization.
The two
o
-Ps intensities
I
3
and
I
4
.
[BMIM
][
Cl
]:Slide14
Plot of the specific volume from PVT experiment under 0
MPa
vs
the mean hole volume at
supercooled
liquid state. The line is a linear fit of the data.
N
h
’ = 0.584
x
10
21
g
-1
V
occ
= 0.8822 cm
3
/g.
[BMIM][Cl]:Slide15
The mean, <
3
>,
and the standard deviation
,
s
3
,
of the
o
-Ps lifetime distribution as a function of temperature
T
during cooling and heating of [BMIM][B(
hfip
)
4
]
.
[BMIM
][B(
hfip
)
4
]:Slide16
[BMIM]
+ [Cl]
- [BF4]-
[PF6]- [OTf]- [NTf2]- [B(hfip)4]-
T
g
(K)(DSC)
225
188-190
190-194
186
T
m
/T
cr
(DSC)
341/290
283/220
286/254
271/232
Tg(PALS)
230 ± 5 K190±3 K
188 ± 3 K 190±5K
Tk335 ± 5 K
280±5 K 285 ± 5 K 270±5 K Tg/T
k
0.687
0.679
0.660
0.704
V
occ_sp
(cm
3
/g)
(PALS)0.88220.75740.6670 0.6405 Nf(1021 g-1)0.5840.4420.376
0.179
V
occ
(Å
3
)(PALS)
256
284
315
446
f
h
(
T
g
)
0.025
(
230 K)
0.030
(190 K)
0.034
(188 K)
0.022
(190 K)
f
h
(
T
k
)
0.070
(
335 K)
0.079
(
280 K)
0.088
(
285 K)
0.061
(
270 K)
Summarized parameters from experiment results for the ionic liquids. Slide17
Hole volumes comparison with molecular volume
[BMIM]
+
[Cl] [BF4]
[PF
6
]
[OTf]
[NTf
2
]
[B(hfip)
4
]
V
m
=
V
(A+X
) (Å3)240
269
30
305
29
327
36
428
36
759
V
([
X
]
) (Å
3
)
47±13
73
9
107
10
129
7
232
15
556
liquid (<
3
>, ns;
<
v
h
>, Å
3
)
2.50
115
5
2.85
150
5
3.03
180
5
3.28
215
5
3.505
240
5
4.35
340
5
glass, 140 K (
3
, ns ;
<
v
h
>, Å
3
))
1.25
36
31.404731.60613 1.60613 crystal (<3> ns) 0.78-1.50/1.251.701.451.70 - 2.00
The hole volumes of various ILs in the liquid (filled circles) and in the glass (140 K, empty circles) states as function of the molecular volume
V
m
=
V
(A
+
X
). The straight lines are linear fits constrained to pass zero, the dashed line shows a quadratic fit.Slide18
Comparison of the mean hole volumes <
v
h
> for the liquid or supercooled liquid and glassy states of the ionic liquids under investigation. Filled symbols: cooling, empty symbols: heating. Free volume calculated by
Fürth
theory is shown as line in the graph.
Hole volume comparison with F
ü
rth
theory
[
Fürth
, R. Mathematical Proceedings of the Cambridge Philosophical Society, 1941.]Slide19
Viscosity and conductivitySlide20Slide21
[BMIM]
+
[Cl] [BF4]
[PF6] [NTf2] Ln()(Pa*s)BT0
Viscosity_VFT
-16.5
2256
162.1
-13.2
1154
149.8
-12.5
1094
166.2
-11.9
810
164.9
Ln(C)
Viscosity_CT
-13.5
0.673
-11.0
0.462
-13.9
0.683
-11.40.313Ln(
)(mS/cm)
BT0Conductivity_VFT 10.72
888
163.6
10.52
914
172.5
9.40
666
170.5
Ln(C)
Conductivity_CT
10.950.51611.580.593
9.30
0.283
/
N
M
/V
m
0.813629
0.644766
0.720126
1.0571
0.9178
0.509612
0.460619
[BMIM]
+
[Cl]
[BF
4
]
[PF
6
]
[NTf
2
]
-16.5
2256
162.1
-13.2
1154
149.8
-12.5
1094
166.2
-11.9
810
164.9
-13.5
0.673
-11.0
0.462
-13.9
0.683
-11.4
0.313
10.72
888
163.6
10.52
914
172.5
9.40
666
170.5
10.95
0.516
11.58
0.593
9.30
0.2830.8136290.6447660.7201261.05710.91780.5096120.460619Slide22
Important
information of the local free volume in the amorphous (glass, supercooled liquid, true liquid) and crystalline phases of ionic liquids as well as the corresponding phase transitions can be obtained from PALS. The o-Ps mean lifetime <
3> shows different behaviour indicating different phases (smaller values in crystalline phase due to dense packing of the material). The parameters I3
also responds to phase transition by sharp value change. Low value in supercooled and true liquid, due to solvation of e+, precursor of Ps.The knee temperature Tk coincidents with melting temperature of corresponding crystalline structure for [NTf2], [PF6] and [Cl] samples.The local free volume from PALS displays a systematic relationship with molecular volume.
Fitting result of viscosity and conductivity by CT equation shows the free volume influence to molecular transport property
.
ConclusionSlide23
More Results:http://positron.physik.uni-halle.de/
Thanks for your time and patience!Slide24
Structural dynamic:
Vogel-
Fulcher
-Tamman (VFT) equation:
= -29.7,
B
= 1339 and
T
0
= 140.8.
T
(
=
max_
o
-Ps
=2.85
ns
)=274 KT
k=280 K
=
-25.8,
B = 731 and T0 = 156. T
(
=
max_
o
-Ps
=3.5
ns
)=271
K
Tk=270 K Slide25
= -34.0,
B
= 2250 and
T0 = 132.T(=max_o-Ps=3 ns
)=289
K
T
k
=285 K
= -26.7,
B
= 1561 and
T
0
=
128.
T
(
=
max_o-Ps=2.5 ns
)=354 KT
k=335 K