Electrical Conductivity of ILs and Their Mixtures

Oscar Cabeza

Facultade de Ciencias

Universidade da Coruña

COST CM 1206 EXIL. Workshop Prague April 21-22

INTRODUCTION

• It is a fundamental characteristic of ILs

• Responsible for all charge transport process

• Not many experimental studies

• Nor theoretical or computational

Here I will tell you what we know about electrical conductivity in ILs,

and what is unknown…

EXPERIMENTAL SET UP

CRISON GLP 31 AND 31+

UNCERTAINTY < 1% REPRODUCIBILITY < 4%

AQUEOUS SOLUTIONS OF Al SALTS UP TO SATURATION

Solid dots correspond to AlI3, open dots to AlBr3, solid squares to AlCl3, and open

squares to Al(NO3) 3 vs. Al3+ concentration in aqueous solutions.

Logarithm of the electrical conductivity vs. 1000/T(K) for selected concentrations.

Symbols represent the same solutions than figure at left. Lines are fits of VTF eq.

J. Vila, E. Rilo, L. Segade, O. Cabeza and L.M. Varela. Electrical conductivity of aqueous solutions of aluminium salts. Physical Review E 71, 31201-31208 (2005).

TEMPERATURE DEPENDANCE OF ILs

Figure 1. Logarithm of the electrical conductivity, Ln s, vs.1000/T(K): (a) EMIM-AlBr3 (x=0.30) (solid squares), EMIM-AlBr3 (x=0.60) (open squares) and EMIM-BF4 (solid triangles). At right, EMIM-AlCl3 (x=0.33) (open circles), EMIM-AlCl3 (x=0.60) (solid circles) and EMIM-ES (open triangles). Lines are

the best fit of the VTF-type equation given

J. Vila, P. Ginés, J.M. Pico, C. Franjo, E. Jiménez, L.M. Varela and O. Cabeza. Temperatura dependence of electrical conductivity in EMIM-based ionic liquids. Evidence of Vogel-Tamman-Fulcher behavior. Fluid Phase Equilibria 242, 141-146 (2006).

𝐿𝑛 𝜎 = 𝐿𝑛 𝜎∞ −𝐸𝑎

𝑘𝐵 𝑇−𝑇𝑔- VTF-type equation

LIQUID TO SOLID TRANSITION

0.01

0.1

1

10

100

1000

250 300 350 400 450 500

T (K)

s (

mS

/cm

)

0

10

20

320 330 340 350

Tm

0.01

0.1

1

10

100

1000

250 300 350 400 450

T (K)

s (

mS

/cm

)

0

10

20

290 330 370

J. Vila, C. Franjo, J.M. Pico, L.M. Varela and O. Cabeza. Temperature behavior of the electrical conductivity of emim-based ionic liquids in liquid and solid states. Portugalae Electrochimica Acta 25, 163-172 (2007).

EMIM-Br EMIM-Cl

EMIM-ES

0.01

0.1

1

10

100

250 300 350 400 450 500

k(m

S/c

m)

T (K)

0

5

10

15

310 330 350 370

EMIM-I 12

13

14

15

16

17

0 200 400 600 800

k(m

S/cm

)

t (s)

0.6

0.7

0.8

0.9

1

1.1

0 200 400 600 800

k(m

S/cm

)

t (s)

0

3

6

9

12

15

0 500 1000 1500

k(mS

/cm)

t (s)

IONIC LIQUID

SOLID CRYSTAL

TRANSITION

0.00001

0.0001

0.001

0.01

0.1

1

10

100

250 300 350 400 450

k(m

S/c

m)

T (K)

0

10

20

260 280 300 320 340

0.00001

0.0001

0.001

0.01

0.1

1

10

100

250 300 350 400 450

k(m

S/c

m)

T (K)

0

2

4

6

270 290 310 330 350

J. Vila, B. Fernández-Castro, E. Rilo, J. Carrete, M. Domínguez-Pérez, J.R. Rodríguez, M. García, L.M. Varela, O. Cabeza. Liquid-solid-liquid phase transition hysteresis loops in the ionic conduct. of ten imidazolium-based ionic liquids. Fluid Phase Equilibria 320, 1-10 (2012)

EMIM-PF6

EMIM-Ty

LIQUID TO SOLID TRANSITION

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

200 250 300 350 400 450

T (K)

s (

mS

/cm

)

0

5

10

15

20

225 250 275 300

EMIM-BF4

0.000001

0.0001

0.01

1

100

200 250 300 350 400 450

T (K)

s (

mS

/cm

)

0.000001

0.00001

0.0001

0.001

0.01

0.1

200 210 220 230 240 250

EMIM-ES

FOR AQUEOUS MIXTURES

Electrical conductivity vs. the weight percentage of water in aqueous IL mixtures. (a) EMIM-AlBr3 (x = 0.35) (solid dots), EMIM-AlBr3, (x = 0.60) (solid squares) and EPYR-AlBr3 (open dots). (b) EMIM-AlCl3 (x = 0.33) (open squares), EMIM-BF4 (solid triangles) and EMIM-ES (open triangles).

J. Vila, P. Ginés, E. Rilo, O. Cabeza , L.M. Varela. Great increase of electrical conduc. of ionic liquids in aqueous solutions. Fluid Phase Equilibria 247, 32-39 (2006).

REVIEW ON EXPERIMENTAL DATA (2011)

0

2

4

6

8

10

0 0.2 0.4 0.6 0.8 1

k(S

/m

)

xIL

Stoppa, 2009. HMIM-BF4

Rilo, 2010a. HMIM-BF4

Stoppa, 2009. BMIM.BF4

Rilo, 2010a. BMIM-BF4

Stoppa, 2009. EMIM-BF4

Rilo, 2010a. EMIM-BF4

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

k (

S/m

)

xIL

Vila, 2006. EMIM-ESLin, 2009. EMIM-ESLin, 2009. EMIM-OTfStoppa, 2009. BMIM-dCy

Electrical conductivity vs. IL molar fraction for three aqueous systems with tetrafluoro borate anions.

Electrical conductivity vs. IL molar fraction for four aqueous systems with different anions.

O. Cabeza, S. García-Garabal, L. Segade, M. Domínguez-Pérez, E. Rilo and L. M. Varela. Physical Properties of Binary Mixtures of ILs with Water and Ethanol. A Review, in “Ionic Liquids Theory, properties, new approaches” (Editor A. Kokorin). Pages 111-136 (2011). Ed. InTech. ISBN: 978-953-307-349-1

WALDEN’S RULE

Molar conductivity vs. molality for aqueous solutions of C2MIM-BF4 (dot

symbols), C4MIM-BF4 (square symbols) and C6MIM-BF4 (triangle symbols).

0

3

6

9

12

15

18

0 1 2 3 4 5

.103

/S ·k

g2·m

-2·m

ol-1

·s-1

m /mol·kg-1

The product of molar conductivity by viscosity vs. molality for aqueous solutions

for the same compounds than at left. Walden’s rule works for each m value!

Walden’s rule:

E. Rilo, J. Vila, J. Pico, S. García-Garabal, L. Segade, L.M. Varela, O. Cabeza. Electrical Conductivity and Viscosity of Aqueous Binary Mixtures of 1-Alkyl-3-methyl Imidazolium Tetrafluoroborate at Four Temperatures. Journal of Chemical Engineering Data 55, 639-644 (2010).

THEORETICAL STUDIES ON IL MIXTURES

L. M. Varela, J. Carrete, M. García, L.J. Gallego, M. Turmine, E. Rilo and O. Cabeza. Pseudo-lattice theory of charge transport in ionic liquid mixtures: corresponding states law for the electric conductivity. Fluid Phase Equilibria 298, 280-286 (2010).

Universal Behavior! No fitting parameters

COMPARATION BETWEEN MIXTURES WITH WATER AND ETHANOL

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5

k/k

max

xa

E. Rilo, J. Vila, S. García-Garabal, L.M. Varela and O. Cabeza. Electrical Conductivity of Seven Binary Systems Containing EMIM-Alkyl Sulfate Ionic Liquids with Water or Ethanol at Four Temperatures. The Journal of Physical Chemistry B 117, 1411-1418 (2013).

SYSTEMATIC STUDIES ON ILs (2007-2013)

0

2

4

6

8

10

1 2 3 4 5 6 7

·

(S·k

g·c

m/m

ol·s

)

c/mol·L-1

Molar conductivity vs. ionic liquid concentration for binary mixtures of ethanol with C2MIM-BF4 (dots), C4MIM-BF4 (squares), C6MIM-BF4 (triangles) and C8MIM-BF4 (rhombus symbols).

The product of molar conductivity by viscosity vs. molality for mixtures with

ethanol for the same compounds than at left. Walden’s rule also works.

E. Rilo, J. Vila, M. García, L. M. Varela and O. Cabeza. Viscosity and electrical conductivity of binary mixtures of CnMIM-BF4 with ethanol at 288 K, 298 K, 308 K and 318 K. Journal of Chemical Engineering Data 55, 5156-5163 (2010).

PRESENT AND FUTURE WORK

O. Cabeza, J. Vila, E. Rilo, M. Domínguez-Pérez, L. Otero-Cernadas, E. López-Lago, T. Méndez-Morales and L.M. Varela. Physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate: a new ionic rigid gel. The Journal of Chemical Thermodynamics 75, 52-57 (2014)

Crystal

Jelly Liquid

Liquid-Crystal evolution

PRESENT AND FUTURE WORK

O. Cabeza, J. Vila, E. Rilo, M. Domínguez-Pérez, L. Otero-Cernadas, E. López-Lago, T. Méndez-Morales and L.M. Varela. Physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate: a new ionic rigid gel. The Journal of Chemical Thermodynamics 75, 52-57 (2014)

PRESENT AND FUTURE WORK

Walden’s rule does not work at all…!

Is it still valid ionic conduction as unique charge transport mechanism?

PRESENT AND FUTURE WORK • To continue studying rigid-gel state and

applications, including optical ones

• To elucidate ionic transport mechanism role from theoretical and experimental points of view

• Computational MD simulations of transport properties (polarizable potential)

• Conductivity of ILs with added salts (first results where presented yesterday by M. Turmine)

• ILs as base compound for new electrolytes

• To begin studying electrical conductivity in DES (Deep Eutectic Solvents)

ACKNOWLEDGEMENT

All authors of any of the papers mentioned, and to Mr. Manuel Cabanas for many wonderful

measurements

THANKS FOR YOUR ATTENTION

COST CM 1206 EXIL. Workshop Prague April 21-22