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Investigation of Ionic Liquids by Positron Annihilation Lif Investigation of Ionic Liquids by Positron Annihilation Lif

Investigation of Ionic Liquids by Positron Annihilation Lif - PowerPoint Presentation

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Investigation of Ionic Liquids by Positron Annihilation Lif - PPT Presentation

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

volume bmim temperature lifetime bmim volume lifetime temperature hole liquid cooling ionic heating function ntf2 experiment standard deviation free

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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

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

31.404731.60613 1.60613 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 conductivitySlide20
Slide21

[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 KT

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 KT

k=335 K