Sorption of Water/Methanol on Teflon and Hydrocarbon Proton Exchange Membranes

Chenfeng He; Frej Mighri; Michael D Guiver; Serge Kaliaguine

doi:10.1021/acsami.6b02543

Sorption of Water/Methanol on Teflon and Hydrocarbon Proton Exchange Membranes

ACS Appl Mater Interfaces. 2016 May 18;8(19):12541-51. doi: 10.1021/acsami.6b02543. Epub 2016 May 6.

Authors

Chenfeng He¹, Frej Mighri¹, Michael D Guiver^{2

3}, Serge Kaliaguine¹

Affiliations

¹ Department of Chemical Engineering, Laval University , Quebec, Quebec G1V 0A6, Canada.
² State Key Laboratory of Engines, Department of Mechanical Engineering, Tianjin University , Tianjin 300072, China.
³ Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) , Tianjin 300072, China.

PMID: 27100675
DOI: 10.1021/acsami.6b02543

Abstract

The sorption of water and methanol droplets on Teflon films, as well as on various representative classes of hydrocarbon-based proton exchange membranes (PEMs) was investigated using contact angle measurement (drop shape method) during wetting under ambient open-air conditions. Teflon films exhibited constant hydrophobic surfaces when contacted with water, but a significant sorption of methanol. The PEMs showed slow sorption of water, and a significant sorption of methanol. The differences in sorption of water and methanol on Teflon and PEMs arose from the match/compatibility in the surface free energies as well as polarities between a liquid and a membrane. The significant discrepancies in surface free energies and polarities between water (72.0 mJ m(-2) and 70.1%, respectively) and Teflon film (14.0 mJ m(-2) and 4.9%, respectively) lead to a highly hydrophobic surface and no discernible sorption of water on Teflon films, while the relative similarity or minor discrepancy in surface free energies and polarities between methanol (22.5 mJ m(-2) and 17.0%, respectively) and Teflon film (14.0 mJ m(-2) and 4.9%, respectively) results in a significant sorption of methanol on Teflon. The surface free energies of PEMs were calculated using the harmonic-mean approach, based on contact angle measurements using both water and diiodomethane as probes. The results show that PEMs have initial surface free energies ranging from 44.1 to 54.0 mJ m(-2) along with polarities in the range of 20.8 to 29.1%, for a selection of typical sulfonated polymers. The surface free energies of ionomers were principally contributed to by the nonpolar component, but the presence of polar groups in the polymer increased the polar component, leading to an increase in surface free energy. Of the PEMs investigated, sulfonated poly(aryl ether ether nitrile) has a higher surface energy than those of other ionomers with similar sulfonate contents. The compatibility between water/methanol and PEMs was investigated on the aspect of surface free energies. The present study provides a plausible strategy to prescreen potential PEMs and optimize membrane electrode assembly (MEA) fabrication.

Keywords: Teflon; absorption; affinity/repellency; capillary; hydrocarbon proton exchange membranes (PEMs); interfacial compatibility/matching; membrane electrode assembly (MEA); methanol; surface free energy (SFE); surface/interface.