swelling kinetic of polymeric membranes in ionic liquids p. izák, Š. hovorka, t. bartovský, l....

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Swelling kinetic of polymeric Swelling kinetic of polymeric membranes in ionic liquids membranes in ionic liquids P. Izák P. Izák , , Š. Hovorka, T. Bartovský, Š. Hovorka, T. Bartovský, L. Bartovsk L. Bartovsk á, á, J. G. Crespo J. G. Crespo

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Page 1: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Swelling kinetic of polymeric Swelling kinetic of polymeric membranes in ionic liquidsmembranes in ionic liquids

P. IzákP. Izák,, Š. Hovorka, T. Bartovský, Š. Hovorka, T. Bartovský, L. BartovskL. Bartovská, á, J. G. CrespoJ. G. Crespo

Page 2: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

The aim

Possibility to obtain new experimental data, which Possibility to obtain new experimental data, which will contribute to better understanding of the swelling will contribute to better understanding of the swelling process.process.

Development of an optical technique allowing follow Development of an optical technique allowing follow

small and even very slow swelling kinetics.small and even very slow swelling kinetics.

Cation - Cation - exchange membrane Nafionexchange membrane Nafion®®, hydrophobic , hydrophobic membranes, membranes, polyurethane-polybutadiene elastomer polyurethane-polybutadiene elastomer ((PU/PBDO) and polydimethylsiloxane (PDMS). PU/PBDO) and polydimethylsiloxane (PDMS).

Page 3: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

IntroductionIntroduction During the transport into the membrane, two During the transport into the membrane, two

ways of mutual affecting of components may be ways of mutual affecting of components may be considered:considered:

The free volume effect, generally increasing the The free volume effect, generally increasing the diffusivity of components (i.e. plasticizing diffusivity of components (i.e. plasticizing effect).effect).

The coupling effect, due to remaining interaction The coupling effect, due to remaining interaction among molecules in the polymer, which can among molecules in the polymer, which can increase or decrease diffusivity of molecules in increase or decrease diffusivity of molecules in the membrane (i.e. the interaction effect).the membrane (i.e. the interaction effect).

Page 4: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Swelling - balance between the forces

where where FFmixmix - force of thermodynamic mixing between the net polymer and the solvent, - force of thermodynamic mixing between the net polymer and the solvent, FFionion – – forces between immobilized and free ions, forces between immobilized and free ions, FFelel – elastic force of the polymer, – elastic force of the polymer, FFintint – inter-– inter-chain attractive forcechain attractive force

The expansion of the polymer is due to the entropic diffusion of its The expansion of the polymer is due to the entropic diffusion of its constituent chains and their counterions.constituent chains and their counterions.

On the other hand, swelling is countered by elastic forces in the On the other hand, swelling is countered by elastic forces in the

chain and inter-chain attractive forces.chain and inter-chain attractive forces.

nContractio

el

Expansion

ionmix FFFFF int

Page 5: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Experimental

Ethyl acetate, ethyl hexanoate, and hexyl acetate were Ethyl acetate, ethyl hexanoate, and hexyl acetate were of analytical grade (Fluka, Germany). of analytical grade (Fluka, Germany).

Room temperature ionic liquids (RTILs): Room temperature ionic liquids (RTILs):

[C[C44mim] [BFmim] [BF44], [C], [C44mim] [PFmim] [PF66], [C], [C88mim] [PFmim] [PF66]]

PU/PBDO, PU/PBDO, PDMS membrane, NafionPDMS membrane, Nafion®® 122 122

Page 6: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Experimental

We looked for ways to promote a micro-turbulence to We looked for ways to promote a micro-turbulence to the binary mixture and thus minimize the the binary mixture and thus minimize the concentration polarizationconcentration polarization at the membrane surface at the membrane surface during pervaporation separation processduring pervaporation separation process

Fine-tuned surface of the dense membrane Fine-tuned surface of the dense membrane bby UV y UV

radiation and application of shear stressradiation and application of shear stress

The fine-tuned surface of the membrane prepared The fine-tuned surface of the membrane prepared from liquid crystalline polyurethane shows primary from liquid crystalline polyurethane shows primary (stripes) and secondary (bands) set of periodic (stripes) and secondary (bands) set of periodic structures, which are perpendicular to each otherstructures, which are perpendicular to each other

Page 7: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Structure of surface modified PU/PBDO blend

PBDO: HO CH2 CH CH CH2 OHy

( ≈ 263 Å)

( ≈ 47 Å)

+

(PU)(PBDO)

Solvent

PU:

CH2 CH O CNH CH3O

NCOOCH3

CH2

H3C

OCN

NHC O

O

CH

CH3

CH2 O CH

CH2 CH2 CH O CNH CH3

NCOCH3

O

Ox

x

x

(Toluene)

ShearY

where

X

Transverse direction

Casting direction

Controlled shear rate (F = 85 N m-2) was then periodically (at least 30 stretching cycles) applied reaching maximum elongation of 1.2

UV radiated (λ = 254 nm) for 24 hours

Page 8: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal

3D topography image (50 × 50 μm2 scan with a image surface area of 2598 μm2) of the PU/PBDO-UV dense membrane in region 2 after pervaporation experiment.

Page 9: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Apparatus for swelling kinetics of membranes

C

MG

SH

TV

TCS

RCT

digital camera

magnifying glass

circle Teflon cell

thermostated vessel infra-red remote control and timer

stand with holders

Page 10: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Table I.Table I. Membrane swelling equilibrium and water saturation of Membrane swelling equilibrium and water saturation of “pure” RTILs at 25°C“pure” RTILs at 25°C

Table II.Table II. Membrane swelling equilibrium of binary mixture Membrane swelling equilibrium of binary mixture [C[C44mim] [BFmim] [BF44] and h] and hexyl acetate at 25°Cexyl acetate at 25°C

Results and discussion

Page 11: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Isotropic swelling kinetics of PU/PBDO

membrane in hexyl acetate at 60°C

0

5

10

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (s)

Rela

tive S

well

ing

y

x

Page 12: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Table III.Table III. Membrane swelling equilibrium of binary mixture Membrane swelling equilibrium of binary mixture [C[C44mim] [BFmim] [BF44] and h] and hexyl acetate aexyl acetate at 60°Ct 60°C

Table IV.Table IV. Membrane swelling equilibrium of binary mixture Membrane swelling equilibrium of binary mixture [C[C44mim] [BFmim] [BF44] and h] and hexyl acetate aexyl acetate at 25°Ct 25°C

Results and discussion

Page 13: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal

Membrane swelling equilibrium with binary

mixture [C4mim] [BF4] and hexyl acetate at 25°C

0

5

10

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (s)

Rel

ativ

e S

wel

lin

g

Series5

Series2

Series1

Series3

xyx mod

y mod

Page 14: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Table V.Table V. Membrane swelling equilibrium of binary mixture Membrane swelling equilibrium of binary mixture [C[C44mim] [BFmim] [BF44] and ethyl] and ethyl hexanoate at 25°C hexanoate at 25°C

Table VI.Table VI. Membrane swelling equilibrium of binary mixture Membrane swelling equilibrium of binary mixture [C[C44mim] [BFmim] [BF44] and ethyl] and ethyl acetate a acetate at 25°Ct 25°C

Results and discussion

Page 15: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal

Swelling equilibrium of Nafion in binary mixture H2O and [C4mim] [BF4] at 25°C

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100

Concentration of H2O in [C4mim] [BF4]

Sw

elli

ng

Eq

ulib

riu

m (

rel.%

)

y rel

x rel

Page 16: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Yeager and Steck 3-phase model of Nafion clusters

[C4mim]+

[C4mim]+

A - fluorocarbon backbonematerial B - large fractional void volume, which containsside-chain material, a small amount of water, and some free sulfonate exchange sites

C - ion clusters, counterionsand sorbed water

Page 17: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Stylized view of polar/nonpolar microphase

separation in a hydrated ionomer

Page 18: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal

Anisotropic swelling and deswelling kinetics of

Nafion membrane in H2O at 25°C

0

2

4

6

8

10

12

14

0 200 400 600 800 1000

Time (s)

Rel

ativ

e S

wel

lin

g

Series1

Series3

x1

y1

x swelling

y swelling

x deswelling

y deswelling

Page 19: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal

Anisotropic swelling and deswelling kinetics of Nafion membrane in binary mixture 50% w/w H2O

and 50% w/w [C4mim] [BF4] at 25°C

0

2

4

6

8

10

12

14

16

18

0 400 800 1200 1600

Time (s)

Rela

tive

Sw

ell

ing

xswelling

yswelling

xdeswelling

ydeswelling

Page 20: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Conclusions Nafion - anisotropic swelling and isotropic swelling of Nafion - anisotropic swelling and isotropic swelling of

PU/PBDO, and PDMS membranes in all measured mixtures PU/PBDO, and PDMS membranes in all measured mixtures

Swelling of Nafion, PU/PBDO, and PDMS membranes is Swelling of Nafion, PU/PBDO, and PDMS membranes is

faster in casting than in transverse directionfaster in casting than in transverse direction

Membrane sMembrane swelling of all polymers increased with the welling of all polymers increased with the

content of ester in all mixtures (RTIL + ester)content of ester in all mixtures (RTIL + ester)

Nafion:Nafion: δδhexyl acetate hexyl acetate > > δδethyl hexanoate ethyl hexanoate >> δδethyl acetateethyl acetate

Page 21: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Conclusions, cont. PU/PBDO, PDMS: PU/PBDO, PDMS: δδhexyl acetate hexyl acetate >>δδethyl hexanoate ethyl hexanoate >>δδethyl acetateethyl acetate

Swelling equilibrium of Nafion membrane in liquid binary mixture Swelling equilibrium of Nafion membrane in liquid binary mixture (([C[C44mim] [BFmim] [BF44]] + + H2O) clearly shows the maximum in the middle ) clearly shows the maximum in the middle of the concentration range at 25°Cof the concentration range at 25°C

This is caused by forming of the larger clusters contains [CThis is caused by forming of the larger clusters contains [C44mim]mim]++ and and HH22OO between hydrophobic and ionic parts of Nafion network between hydrophobic and ionic parts of Nafion network

It was observed only little increase of polymer swelling with It was observed only little increase of polymer swelling with temperaturetemperature

Page 22: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

Acknowledgement

The financial support of The financial support of the FEDER through the the FEDER through the project grant project grant (POCTI/EQU/35437/1999) is gratefully (POCTI/EQU/35437/1999) is gratefully acknowledged. P. Izák would like to acknowledge acknowledged. P. Izák would like to acknowledge the post-doc grant (SFRH/BPD/9470/2002) from the post-doc grant (SFRH/BPD/9470/2002) from Fundação para a Ciência e a Tecnologia, PortugalFundação para a Ciência e a Tecnologia, Portugal..

The co-authors from Czech Republic acknowledge The co-authors from Czech Republic acknowledge the financial support from the MSM 2234 00008 the financial support from the MSM 2234 00008 grant from Ministry of Education of the Czech grant from Ministry of Education of the Czech Republic.Republic.

Page 23: Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo

FCT - Universidade Nova de Lisboa Portugal