Presentation on theme: "Swelling kinetic of polymeric membranes in ionic liquids"— Presentation transcript:
1 Swelling kinetic of polymeric membranes in ionic liquids P. Izák, Š. Hovorka, T. Bartovský, L. Bartovská, J. G. Crespo
2 The aimPossibility to obtain new experimental data, which will contribute to better understanding of the swelling process.Development of an optical technique allowing follow small and even very slow swelling kinetics.Cation - exchange membrane Nafion®, hydrophobic membranes, polyurethane-polybutadiene elastomer (PU/PBDO) and polydimethylsiloxane (PDMS).
3 IntroductionDuring the transport into the membrane, two ways of mutual affecting of components may be considered:The free volume effect, generally increasing the diffusivity of components (i.e. plasticizing effect).The coupling effect, due to remaining interaction among molecules in the polymer, which can increase or decrease diffusivity of molecules in the membrane (i.e. the interaction effect).
4 Swelling - balance between the forces where Fmix - force of thermodynamic mixing between the net polymer and the solvent, Fion – forces between immobilized and free ions, Fel – elastic force of the polymer, Fint – inter-chain attractive forceThe expansion of the polymer is due to the entropic diffusion of its constituent chains and their counterions.On the other hand, swelling is countered by elastic forces in the chain and inter-chain attractive forces.
5 ExperimentalEthyl acetate, ethyl hexanoate, and hexyl acetate were of analytical grade (Fluka, Germany).Room temperature ionic liquids (RTILs):[C4mim] [BF4], [C4mim] [PF6], [C8mim] [PF6]PU/PBDO, PDMS membrane, Nafion® 122
6 ExperimentalWe looked for ways to promote a micro-turbulence to the binary mixture and thus minimize the concentration polarization at the membrane surface during pervaporation separation processFine-tuned surface of the dense membrane by UV radiation and application of shear stressThe fine-tuned surface of the membrane prepared from liquid crystalline polyurethane shows primary (stripes) and secondary (bands) set of periodic structures, which are perpendicular to each other
7 Structure of surface modified PU/PBDO blend Controlled shear rate (F = 85 N m-2) was then periodically (at least 30 stretching cycles) applied reaching maximum elongation of 1.2UV radiated (λ = 254 nm) for 24 hoursSolvent+≡XTransversedirectionCasting direction(Toluene)(PBDO)(PU)YwhereShear( ≈ 47 Å)PU:PBDO:≡( ≈ 263 Å)
8 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.FCT - Universidade Nova de Lisboa Portugal
9 Apparatus for swelling kinetics of membranes MGSHTVTCSRCTdigital cameramagnifying glasscircle Teflon cellthermostated vesselinfra-red remote control and timerstand with holders
10 Results and discussion Table I. Membrane swelling equilibrium and water saturation of “pure” RTILs at 25°CTable II. Membrane swelling equilibrium of binary mixture [C4mim] [BF4] and hexyl acetate at 25°C
11 Isotropic swelling kinetics of PU/PBDO membrane in hexyl acetate at 60°C
12 Results and discussion Table III. Membrane swelling equilibrium of binary mixture [C4mim] [BF4] and hexyl acetate at 60°CTable IV. Membrane swelling equilibrium of binary mixture [C4mim] [BF4] and hexyl acetate at 25°C
13 FCT - Universidade Nova de Lisboa Portugal Membrane swelling equilibrium with binary mixture [C4mim] [BF4] and hexyl acetate at 25°CFCT - Universidade Nova de Lisboa Portugal
14 Results and discussion Table V. Membrane swelling equilibrium of binary mixture [C4mim] [BF4] and ethyl hexanoate at 25°CTable VI. Membrane swelling equilibrium of binary mixture [C4mim] [BF4] and ethyl acetate at 25°C
15 FCT - Universidade Nova de Lisboa Portugal Swelling equilibrium of Nafion in binary mixture H2O and [C4mim] [BF4] at 25°CFCT - Universidade Nova de Lisboa Portugal
16 Yeager and Steck 3-phase model of Nafion clusters A - fluorocarbon backbonematerialB - large fractional void volume, which containsside-chain material, a smallamount of water, and somefree sulfonate exchange sitesC - ion clusters, counterionsand sorbed water[C4mim]+[C4mim]+
17 Stylized view of polar/nonpolar microphase separation in a hydrated ionomer
18 FCT - Universidade Nova de Lisboa Portugal Anisotropic swelling and deswelling kinetics of Nafion membrane in H2O at 25°CFCT - Universidade Nova de Lisboa Portugal
19 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°CFCT - Universidade Nova de Lisboa Portugal
20 ConclusionsNafion - anisotropic swelling and isotropic swelling of PU/PBDO, and PDMS membranes in all measured mixturesSwelling of Nafion, PU/PBDO, and PDMS membranes is faster in casting than in transverse directionMembrane swelling of all polymers increased with the content of ester in all mixtures (RTIL + ester)Nafion: δhexyl acetate > δethyl hexanoate > δethyl acetate
21 Conclusions, cont.PU/PBDO, PDMS: δhexyl acetate >δethyl hexanoate >δethyl acetateSwelling equilibrium of Nafion membrane in liquid binary mixture ([C4mim] [BF4] + H2O) clearly shows the maximum in the middle of the concentration range at 25°CThis is caused by forming of the larger clusters contains [C4mim]+ and H2O between hydrophobic and ionic parts of Nafion networkIt was observed only little increase of polymer swelling with temperature
22 AcknowledgementThe financial support of the FEDER through the project grant (POCTI/EQU/35437/1999) is gratefully acknowledged. P. Izák would like to acknowledge the post-doc grant (SFRH/BPD/9470/2002) from Fundação para a Ciência e a Tecnologia, Portugal.The co-authors from Czech Republic acknowledge the financial support from the MSM 2234 00008 grant from Ministry of Education of the Czech Republic.