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

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.

Alcohol-Treated Porous PTFE Substrate for the Penetration of PTFE-Incompatible Hydrocarbon-Based Ionomer Solutions

“…Then, the surface property of PTFE substrate is instantaneously tuned to alcohol-like before the complete evaporation of the applied alcohol. 54 Indeed, after applying alcohol solvents, significant decreases in the contact angles of the SPAES50 solutions at all concentrations were observed on the alcohol-treated PTFE compared to the pristine PTFE, as shown in Figure 3. The contact angles on F-MeOH, F-EtOH, and F-NPA were 67.1, 64.5, and 60.6°at 5 wt %, respectively, about a half value on the untreated pristine PTFE.…”

“…In this process, the alcohol solvents were simply spread on PTFE to coat the pore surface by applying solvents. Then, the surface property of PTFE substrate is instantaneously tuned to alcohol-like before the complete evaporation of the applied alcohol . Indeed, after applying alcohol solvents, significant decreases in the contact angles of the SPAES50 solutions at all concentrations were observed on the alcohol-treated PTFE compared to the pristine PTFE, as shown in Figure .…”

The effect of polydopamine coated multi‐walled carbon nanotube on the wettability of sulfonated poly(ether ether ketone) nanocomposite as a proton exchange membrane

“…27 Guiver and et al studied the crossover of methanol by estimating the SFE of PEM and interfacial free energy with water and methanol. 28 In 2011, Varughese and et al explored the correlation between SFE and the proton conductivity of the blend membrane of sulfonated polyvinyl alcohol with different sulfonation degrees and SPEEK. They stated that increasing the ion exchange capacity increases the surface energy of the blends membrane while the proton conductivity is decreased.…”

Fast Proton Conduction in Denatured Bovine Serum Albumin-Coated Nafion Membranes

“…BSA presents good adsorption ability on the hydrophobic surface of the Nafion 117 membrane. 39 Denaturation of BSA is further utilized to adjust the BSA secondary structures and immobilize the BSA modification layer. The obtained BSA−N117 membranes show excellent thermal stability as well as good resilience between dry and hydrated states.…”

“…Herein, a series of BSA surface-modified Nafion 117 composite membranes (BSA–N117) are conveniently and eco-friendly prepared with BSA aqueous solutions at different concentrations. BSA presents good adsorption ability on the hydrophobic surface of the Nafion 117 membrane . Denaturation of BSA is further utilized to adjust the BSA secondary structures and immobilize the BSA modification layer.…”