swelling kinetic of polymeric membranes in ionic liquids p. izák, Š. hovorka, t. bartovský, l....
TRANSCRIPT
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
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).
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).
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
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
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
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
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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.
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
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
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
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
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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
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
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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
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
Stylized view of polar/nonpolar microphase
separation in a hydrated ionomer
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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
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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
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
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
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.
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