Low Gas Permeability Research Articles

Development of Blend Nanofiber Composite Polymer Electrolyte Membranes with Dual Proton Conductive Mechanism and High Stability for Next-Generation Fuel Cells

Blend polymer nanofibers (BNF), consisting of sulfonated polyimide and polybenzimidazole blends doped with phytic acid, were fabricated and composed with Nafion to give BNF composite membranes for polymer electrolyte fuel cells. The BNF composite membrane possessed high mechanical and chemical stabilities and low gas permeability. In addition, the BNF composite membrane showed higher proton conductivity than the commercial Nafion NR211 membrane, not only at low temperatures but also at high temperatures above 100 °C and low relative humidity (ca. 10% RH). The proton conduction mechanism in the BNF composite membranes was examined and revealed that proton hopping conduction occurred besides the vehicle mechanism in the BNF composite membranes. The BNF composite membrane provided improved fuel cell performances compared to the cell using the conventional Nafion NR211 membrane at high humidity, low humidity, and high temperature/low humidity, suggesting the potential of BNF composite membranes for next-generation fuel cells.

Stretchable and Robust Silver Nanowire Composites on Transparent Butyl Rubber

Silver nanowires (AgNWs) are leading materials for transparent conductive electrodes in optoelectronic devices. The solution processability of AgNWs combined with the optical transparency and electrical conductivity of solution-deposited AgNW networks makes them a promising alternative to conventional indium tin oxide. Furthermore, the ability of AgNW networks to withstand mechanical deformation means that AgNW networks may be the material of choice for next-generation flexible and stretchable optoelectronics. The drawback with the practical use of AgNWs, however, is that corrosion of AgNWs under ambient conditions damages the AgNW network and reduces the workable life span. Environmental degradation is especially problematic in stretchable electronics, which use elastomeric substrate materials that have a high gas permeability like poly(dimethylsiloxane) (PDMS). Covering individual AgNWs with a protective nanoscale coating to prevent corrosion complexifies their preparation and implementation in practical applications. This study presents an alternative approach in which the elastomeric substrate, transparent butyl rubber (TBR), acts as both a stretchable substrate and a protective gas barrier. TBR, an optically transparent formulation of poly(isobutylene-co-isoprene), is a synthetic rubber with an intrinsically low gas permeability. We demonstrate that AgNW networks embedded in a polyurethane adhesive and adhered to a TBR substrate provide high conductivity and optical transparency and are robust to tensile strain as well as extreme environments of humidified air, underwater storage, and corrosive acid vapors. We show that this system outperforms a comparison system that uses PDMS instead of TBR.

Durable and highly-efficient anion exchange membrane water electrolysis using poly(biphenyl alkylene) membrane

Anion exchange membrane water electrolysis (AEMWE) is a promising technology for large-scale green-hydrogen production, owing to high current density, low gas permeability and low capital cost. High-performance and durable anion exchange membrane (AEM) is the key to bringing it into practical utilization. In this study, poly(biphenyl alkylene) (PBPA) AEM is synthesized and used for the highly-efficient and durable AEMWE. The fabrication conditions of membrane electrode assembly (MEA) and working condition of water electrolysis are investigated in detail. The ionomer contents and electrolyte type significantly affect the performance and durability of the PBPA-based AEMWE cell. The as-fabricated AEMWE cell with the PBPA membrane achieves a current density as high as 4.0 A cm−2 @ 2.0 V in 1 M KOH at 80 °C and a continuous water electrolysis of over 3,500 h at 1.0 A cm−2 with a slow voltage rising rate of 6.5 μV h−1. The high performance and long durability exhibit that the PBPA-based AEM is promising towards the industrial hydrogen production.

Synthesis and gas separation performance of Tröger's base-containing polyimides derived from 9,9-Bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride

Two imide-containing diamine monomers were prepared using 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride (6FcDA) and 2,6-dimethylaniline or 2,6-diisopropylaniline as the starting materials. Two polyimides of intrinsic microporosity (PIM-PIs), i.e., 6FcDA-Me2NH2-TB and 6FcDA-iPr2NH2-TB, were then synthesized via TB polymerization of imide-containing diamines and dimethoxymethane in trifluoroacetic acid. The surface areas, fractional free volumes, and interchain distances of the PIM-PIs were in the range of 555–569 m2 g−1, 0.16–0.20, and 0.60–0.67 nm, respectively. These values followed the order of 6FcDA-Me2NH2-TB < 6FcDA-iPr2NH2-TB owing to the larger size of isopropyl substituents relative to methyl groups. Furthermore, 6FcDA-Me2NH2-TB exhibited obvious π-π stacking interactions as evidenced by the diffraction peaks at ∼ 26 ° in wide angle X-ray diffraction patterns. Consequently, 6FcDA-Me2NH2-TB showed higher perm-selectivity but lower gas permeability as compared to 6FcDA-iPr2NH2-TB. Particularly, both polymers had a CO2 permeability of > 2900 Barrer and a CO2/CH4 selectivity of > 10, located between the 1991 and 2008 Robeson’s upper bound for CO2/CH4 separation.

Structural engineering on 6FDA-Durene based polyimide membranes for highly selective gas separation

In this work, four diamine monomers, selected based-on steric hindrance and affinity with gas to be separated, were separately introduced into 6FDA-Durene to prepare co-polyimides. The influences of incorporating diamine monomer geometry on free volume elements (FFV, FAV, cavity size distribution, surface area and cavity connectivity) and gas transport properties (solubility and diffusion) of synthesized co-polyimide membranes were systematically investigated. The introduction of second amino monomer can increase gas selectivity, however leaded to lower gas permeability. Gas solubility and solubility selectivity of membrane remained almost stable with introduction of different amino monomer. While the gas diffusion changed remarkably, and the diffusion selectivity increased by about 170%. The FDDA membrane with crown ether structure displayed the highest gas selectivity (increased by 122%, 121%, 158%, 115% and 115% for H2/N2, H2/CH4, O2/N2, CO2/N2 and CO2/CH4, respectively, compared to 6FDA-Durene membrane), whose selectivity was relatively high among the PI-based membranes. This can be explained that the crown ether group granted the membrane with largest FAV ratio of specific gas pair, as well as the smallest pore size that would cause stronger size sieving effect. These results indicated that gas separation property of polyimide membranes can be effectively adjusted via tuning monomer structure, which is easily synthesized or has been commercialized, to realize the industrial application of membrane-based gas separation.

Influence of two-phase displacement characteristics on the storage efficiency and security of geological carbon storage

In the mitigation of greenhouse gas emissions, the storage efficiency and security of geological carbon storage (GCS) are the focus of attention, and both of them are closely related to the displacement behavior between immiscible two phases. In this study, CO2-water two-phase displacement experiments were conducted on six samples with various pore structures using nuclear magnetic resonance and magnetic resonance imaging technology to characterize the fluid distribution and determine displacement patterns. The displacement property was found to be closely related to the heterogeneity and anisotropy of pore structure. The two-phase displacement instability gradually evolved from tonguing (logCa > −2.94) to capillary fingering (logCa < −2.03), and then further evolved into viscous fingering (logCa > −2.03). Nevertheless, rocks with good connectivity and high permeability will restrain the occurrence of unstable displacement even if logCa is in the favorable range. Combined analyses of displacement patterns and pore structure can provide effective means for the evaluation of reservoir and caprock. For rocks dominated by micropores, their displacement pattern is more likely to correspond to time-consuming piston-like displacement. Their high sealing efficiency is characterized by high capillary displacement pressure and low effective gas permeability, which allow them to be considered as caprocks. For rocks with lower capillary displacement pressure and higher effective gas permeability, their lower residual water saturation makes them more suitable as favorable reservoirs for GCS. Reservoir rocks with stable piston-like displacement exhibit the highest displacement efficiency, while the difference of displacement rates in pores with diverse sizes caused by the fingering or tonguing phenomena weakens the displacement efficiency.

Expanded graphite (EG)/Ni@Melamine foam (MF)/EG sandwich-structured flexible bipolar plate with excellent electrical conductivity, mechanical properties, and gas permeability

The bipolar plate is an important component of the fuel cell. Composite graphite-based bipolar plates with adjustable properties are potential candidates to realize the high performance of the cell. However, simultaneously improving the electrical and mechanical properties of the plate is always the focus and difficulty of the research since they tend to behave with mutual inhibition. Here in this work, we report a laminating strategy to prepare composite bipolar plates with the (EG)/Ni@Melamine foam (MF)/EG sandwiched structure. The highly porous MF sponge provides enough space for epoxy immersion and the Nickel plating improves the electrical conductivity. Both the electrical conductivity (320 S/cm) and the flexural strength (56 MPa) are improved compared to the original EG plate. The enriched resin amount in the intermedium layer also ensures lower gas permeability (2.16 × 10−9 cm3cm−2s−1). In addition, owing to the residual resin on the surface of the developed plate, there is a smaller, indicating better wettability. Further practical performance tests proved that the developed plate has favorable performance under actual working conditions compared to commercialized carbon graphite plate.

Sulfonated Poly(Phenylene sulfone) blend membranes finding their way into proton exchange membrane fuel cells

We demonstrate performance and durability of a fluorine-free poly(phenylene-sulfone) membrane for proton exchange membrane fuel cells. Sulfonated poly(phenylene-sulfone) (EW 220 g·eq−1; sPPS-220) has been prepared and processed by acid/base blending with 25 wt% poly(benzimidazole) (sPPS-220/PBI-O). A blend membrane with a nominal EW 463 g·eq−1(ion exchange capacity of 2.16 meq·g−1) has been fabricated by solution co-casting on a commercial production line. Blend component fractions are chosen to meet Nafion 211's specific conductivity and obtain mechanical robustness. Blend membrane has significantly lower gas permeability than Nafion under both dry (RH = 30%) and wet (RH = 95%) conditions, significantly higher storage modulus and no softening at high temperature. Like pure-sPPS, blend membrane is hydrolytically stable up to T = 180 °C in water. Single-cell H2/air fuel cell tests demonstrate higher open-circuit voltage and similar performance under load conditions compared to Nafion. Still, high mass transport polarization is likely due to water condensation at the cathode side. This increases membrane swelling and thus electroosmotic water drag reducing hydration at the anode side and leading to flooding of the cathode. Under accelerated stress conditions at low relative humidity, sPPS-220/PBI-O is more durable than Nafion. Possible explanations are i) lower gas crossover reduced radical formation rate and ii) high intrinsic stability of sPPS.

Novel Method for Deposition of Gas-Tight SiC Coatings

A new high-temperature method for the deposition of gas-tight silicon carbide protective coatings with low gas permeability has been developed. The free carbon atoms form during the high-temperature pyrolysis of hydrocarbon molecules. In turn, carbon reacts with molten silicon contained in the subsurface substrate layers and/or with silicon vapor. The source of silicon vapor serves the molten silicon in the heated zone of a reactor furnace. Such coatings effectively protect SiC-C-Si and SiC-C-MoSi2 ceramics, carbon–carbon composite materials, structural graphite, and refractory metals and alloys from oxidation. The conducted tests show the high thermal oxidation and thermal shock stability of deposited protective coatings, as well as their good adhesion to the substrates.

Mechanism of improving quality of dry-aged pork loins in scoria-containing onggi, Korean earthenware as a storage container.

Many scientists have investigated solutions to reduce microbiological risks in dry-aged meat after the dry-aging technology was revived for high quality and value-added premium meat product in the market. This study aimed to investigate the effect of scoria powder in onggi (Korean earthenware) on the meat quality of pork loins during 21 days of dry aging and to elucidate its mechanism of action. The pork loins were randomly divided into three groups: aged in vacuum-packaging, onggi containing red clay only (OR), and onggi containing 30% red clay and 70% scoria powder (OS). Microbial analyses (total plate count and Lactobacillus spp.) and physicochemical analyses (pH, shear force, volatile basic nitrogen [VBN], water activity, 2-thiobarbituric acid reactive substances, water content, water holding capacity, cooking loss, and color analysis) of aged meat were conducted. Far-infrared ray emission, quantification of immobilized L. sakei and microstructure of onggi were investigated to understand the mechanism. On day 21, the meat aged in OS exhibited lower pH, shear force, VBN, and water activity than those aged in OR, along with an increase in the number of Lactobacillus spp. OS had a smaller pore diameter than OR, implying lower gas permeability, which could promote the growth of L. sakei. OS improved the microbiological safety and storage stability of pork loin during dry aging by increasing number of Lactobacillus spp. possibly due to low permeability of OS.

A bio-hydro-chemical model for gas pressure development in municipal solid waste landfills

Prediction of gas pressure development within municipal solid waste (MSW) landfills is of great importance for the stability analysis and design of gas collection systems. This study presents a fully coupled bio-hydro-chemical model for the gas pressure development in landfills. The reduction of foam on the relative gas permeability and the variation of the intrinsic permeability with degradation degree are considered. The source terms in the governing equations of two-phase flow and solute transport are chosen from the biodegradation process of MSW. Both one-step landfilling and multi-step landfilling are calculated to compare the differences. It is found that the fast hydrolysis of fresh MSW produces most of the volatile fatty acids (VFAs) and leachate within the first 2 months. During multi-step landfilling, the VFA and leachate produced from fresh MSW in the top flow downward to the bottom, leading to high gas production and high leachate saturation in the deep. Meanwhile, the high concentration of VFA reduces the surface tension of the leachate, enabling it to generate foam and further reduce gas permeability. Owing to the high gas production and low gas permeability, the excess gas pressure is easily developed in the deep layer. The maximum gas pressure of multi-step landfilling is about 2·5 times that of one-step landfilling. Case studies of the laboratory column test and in situ borehole test verify the accuracy of the model in predicting the temporal and spatial distribution of gas pressure. For the slope failure induced by high gas pressure, the evolution of shear strength and stability during a 2 year landfilling period is calculated and discussed.

Construction of compostable packaging with antibacterial property and improved performance using sprayed coatings of modified cellulose nanocrystals

Increasing concerns about food safety and the environment have facilitated the development of eco-friendly antibacterial packaging. This study aimed to demonstrate a facile way to fabricate active packaging materials with modified cellulose nanocrystals (CNCs) and compare the effects of different modified CNCs on the performance of compostable materials. Polylactic acid (PLA) film was selected as a model, and CNCs were modified with methacrylamide, cetyltrimethylammonium bromide, and zinc oxide, respectively, and then applied on the surface of PLA films by spray-coating. All modified CNCs showed excellent antibacterial activity against S. aureus and E. coli (>99.999 %). The effects of different CNC modifications on the performance of PLA films were investigated. Compared to neat PLA films, PLA/CNC films exhibited improved mechanical strength with maintained flexibility, lower gas permeability, and faster compost disintegration rate, and extended the shelf life of wrapped pork samples from 3 days to >10 days. Therefore, this work will also facilitate the applications of PLA materials in eco-friendly packaging.

Improvement of the well cementing technology, increasing the reliability of the annule isolation and preserving the permeability of the reservoir

The article presents measures to improve the quality of cementing the production string of high-performance wells. The relevance of the proposed technological solutions is substantiated. The results of experimental studies of the installation simulating the processes occurring during the thickening of the cement slurry under the action of gravitational forces are presented. An algorithm for creating overpressure on the wellhead during fastening of the production string is proposed. The compositions of process fluids are described, which increase the reliability of the annular space isolation and preserve the permeability of the reservoir, and provide the main data on the results of their laboratory studies. For cementing the annular space of the production string, the composition of the expanding cement slurry has been developed and the procedure for its preparation has been established. The proposed solution has low water separation and high sedimentation resistance; has adjustable rheological parameters. Cement stone is characterized by low gas permeability and high strength properties.

Improvement of the well cementing technology

The article presents measures to improve the quality of cementing the production string of high-performance wells. The relevance of the proposed technological solutions is substantiated. The results of experimental studies of the installation simulating the processes occurring during the thickening of the cement slurry under the action of gravitational forces are presented. An algorithm for creating overpressure on the wellhead during fastening of the production string is proposed. The compositions of process fluids are described, which increase the reliability of the annular space isolation and preserve the permeability of the reservoir, and provide the main data on the results of their laboratory studies. For cementing the annular space of the production string, the composition of the expanding cement slurry has been developed and the procedure for its preparation has been established. The proposed solution has low water separation and high sedimentation resistance; has adjustable rheological parameters. Cement stone is characterized by low gas permeability and high strength properties.

Efficient degassing and ppm-level oxygen monitoring flow chemistry system.

Low oxygen levels are critical for a long range of chemical transformations carried out in both flow and batch chemistry. Here, we present an inline continuous flow degassing system based on a gas-permeable membrane inside a vacuum chamber for achieving and monitoring ppm-level oxygen concentrations in solutions. The oxygen presence was monitored with a molecular oxygen probe and a continuously running UV-vis spectrometer. An automated setup for discovering optimal reaction conditions for minimal oxygen presence was devised. The parameters tested were: flow rate, vacuum pressure, solvent back-pressure, tube material, tube length and solvent oxygen solubility. The inline degassing system was proven to be effective in removing up to 99.9% of ambient oxygen from solvents at a flow rate of 300 μl min-1 and 4 mbar vacuum pressure inside the degassing chamber. Reaching lower oxygen concentrations was limited by gas permeation in the tubing following the degassing unit, which could be addressed by purging large volume flow reactors with an inert gas after degassing or by using tubing with lower gas permeability, such as stainless steel tubing. Among all factors, oxygen solubility in solvents was found to play a significant role in achieving efficient degassing of solvents. The data presented here can be used to choose optimal experimental parameters for oxygen-sensitive reactions in flow chemistry reaction setups. The data were also fitted to an analytically derived model from simple differential equations in physical context of the experiment.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE EFFECT OF DELAMINATION DEFECT AT MATERIALS OF POLYETHYLENE TEREPHTHALATE (PET)PRODUCED BY ADDITIVE MANUFACTURING ON FLEXURAL RESISTANCE

Polyethylene terephthalate (PET) material, which is widely used in the packaging industry due to its thermal and mechanical properties, high chemical resistance, and low gas permeability, is among the most widely used polymer materials in the world. These properties have made their use in additive manufacturing methods widespread. Determining how some common additive manufacturing defects affect the products produced by these methods will increase the adoption of these technologies in the final product production. In this study, the investigation of the effect of layer non-joining defect called delamination on the impact strength of PET material produced by additive manufacturing method at different layer thicknesses was carried out experimentally and numerically. The effects to flexural stress on the artificially created layer adhesion defect on the middle layers of the parts produced and modeled with a layer thickness of 0.1/0.2/0.3mm were investigated. It has been observed that the increase in layer thickness decreases flexural strength. In addition, while the flexural strength of the specimens containing delamination decreased, the increase in layer thickness accelerated this decrease.

Swelling and softening behavior of iron ore-spent mushroom substrate composite pellets during carbothermal reduction

In the present day, we have reached close to an optimum condition of CO2 emission when using coal or coke for iron making process. Carbon neutrality is achieved during carbothermal reduction by employing biomass as a reducing agent in composite pellets. The swelling behavior of composite pellets during reduction has detrimental effects, and catastrophic swelling leads to subsequent disintegration of pellets, which causes low gas permeability through packed beds in the industry. In this study, we used coal, spent mushroom substrate, torrefied mushroom substrate (300 °C), and de-ashed torrefied mushroom substrate as reducing agents in our iron-ore composite pellets. Volume change of the composite was investigated with heating profile (15 °C/min until 1350 °C), reduction time is 70min, the maximum swelling observed in torrefied mushroom pellets is +158%, the pellets experienced swelling in between (700°C–1000 °C) and started to soften from 825 °C. However, no swelling is observed in the coal and de-ashed torrefied pellet. On the other hand, de-ashed torrefied pellets with the addition of alkali metal oxides and soda lime glass had significant swelling and decrease in softening temperature. With the presence of Na2O and K2O in pellets ash, during reduction in some localized areas, they form low melting slags like Soda-lime (∼1000 °C) and Potash-lime (∼1200 °C) compositions. These slags start to soften at a low temperature ∼700 °C for soda-lime composition. As the temperature increases, viscosity decreases, which causes pellets to soften more, and parallelly gas evolving from the pellet during reduction (mainly CO product of the Boudouard reaction) causes these slags to expand, like a glass blowing mechanism.

Simulation and Experiment of CO2 Philicity and Separation in Carbonate-Rich Polymers

Functional polymers containing CO2-philic groups are of great interest for membrane CO2/gas separation for carbon capture. This work, for the first time, systematically elucidates the effect of carbonate groups on CO2/gas solubility selectivity and permselectivity using an integrated simulation and experimental approach in two carbonate-rich polymers: poly(ethylene carbonate) (PEC) and poly(propylene carbonate) (PPC). Both polymers are amorphous and rubbery at 35 °C, and they are thoroughly characterized for physical properties and CO2/gas separation properties. PEC exhibits a CO2/C2H6 solubility selectivity of 24 at 35 °C, much higher than that of poly(ethylene oxide) (2.8), one of the leading membrane materials for CO2/gas separation. The binding energy between gas molecules and polymer analogue was calculated using density functional theory (DFT), and the results are consistent with the experimental sorption data. Both PEC and PPC show CO2/CH4 permselectivity of ≈53 at 35 °C, the highest reported for rubbery polymers. PEC also exhibits a CO2/N2 permselectivity of 74, one of the best reported in the literature. Although polar carbonate groups may lower gas permeability, they can be incorporated into polymer architectures to improve CO2/gas selectivity.

(Invited) Cold Atmospheric Plasma Jet Sources with a Flexible Matrix

Plasma is an ionized gas containing free electrons, ions, neutral species (atoms, molecules, radicals), photons from UV to infrared wavelengths. Its composition makes it a rich environment for reactive process, showing a collective response to external perturbations. Low temperature plasmas are hot electron gas (1-10 eV) which are not in thermal equilibrium with the other cold part of the atomic or molecular species (0.02 eV). These cold plasmas are then suitable for applications to delicate surfaces (skin) without damage, especially since RONS (Reactive Oxygen and Nitrogen Species) show healing properties. Biomedicine is facing new challenges like decontamination, wound healing, and oncotherapy. Plasma medical treatments are selective, instantaneous, tunable in comparison to lasers and chemicals. There is a big need for developing new plasma sources that can treat complex surfaces (with asperities, sharp edges, cavities, complex accessibility)For this purpose, two types of flexible Cold Atmospheric Plasma Jet (CAPJ) sources with different geometries (planar and radial) were made and characterized through: multijet length and flow regime, electrical parameters, Optical Emission Spectroscopy (OES), performance after bending the aerogel. He (99.995%) was used in both configurations. Finite Element Method simulations were run to predict and understand the electromagnetic process in this plasma jet configuration.In planar geometry, DBD (Dielectric Barrier Discharge) was constituted of a silica aerogel placed between two biased electrodes. Silica aerogel has a very low gas permeability and is mechanically stable (highly cross-linked fiber glass network). Plasma jets constituted of 3 aligned jets, a few mm long above the DBD region whose length is proportional to the He flow rate, flowing in laminar regime, were produced by Helium flow (flow rate: 1-4 slm) subjected to sinusoidal voltage of 5kV and 15kHz frequency. Higher flow rate produced turbulent flows. The ratio between gas velocity and discharge voltage can be adjusted: short jets (flow limited operation) are suitable for near surface treatments, longer jets (power limited operation) are appropriate for greater distance treatments. OES showed strong N2 emission. Planar DBD was studied in flat configuration then its flexibility was characterized in bent (concave, convex) configurations. Compliance of the plasma source is limited by aerogel size and thickness. There is possibility to extend the device from 1D to 2D (matrix of plasma jet lines).In radial geometry, DBD was constituted of a soft hollow cylinder (about 5 cm external diameter, 2.5 cm internal diameter and 10 cm long), made of polyethylene (PE) foam, material selected for its flexibility and low permeability. An aluminum/dielectric coated rod electrode was placed in the core of the cylinder, copper circular electrodes were disposed on the external cylinder wall at 15 mm distance from each other surrounding 1mm holes punched in the PE cylinder, where the CAPJs were formed. In this geometry, two different operations modes were apprehended: comb mode was represented by four equidistant axial CAPJs and round brush mode was experienced when three CAPJs were aligned at constant azimuthal angle. In this case, discharges were triggered at 15 kHz AC voltage and a lower voltage than in planar configuration (3.8 kV). The jets were uniform in length and intensity. OES were recorded in the active region (inside the PE housing) and in the afterglow region. In the afterglow region, the spectrum was similar to the one obtained in planar geometry. A preponderance of hydroxyl groups (OH), nitrogen molecules (N2, N2 +), He atoms was found. The source remains stable after deformation of the PE housing.The feasibility of these flexible plasma sources in radial and axial configurations is promising for treating any kind of surface with special topography.

(Invited) Structure-Property Relationships in Highly Permeable Dioxolane-Based Perfluorinated Ionomers

Ion conducting polymers used as membranes and catalyst binders in membrane electrode assemblies (MEAs) have driven continuous improvements in fuel cell performance. Commercially available membrane materials (e.g., Nafion®) impart low gas permeability, high chemical and mechanical stability thanks to their semi-crystalline polytetrafluoroethylene (PTFE) matrix. This dense matrix also slows permeation of gases through the polymer, introducing significant mass-transport losses in the catalyst layers and limits fuel cell performance. In this presentation, I will discuss a new family of perfluorinated ionomers that incorporates an amorphous matrix based on a perfluoro(2-methylene 4-methyl-1,3-dioxolane) (PFMMD) backbone. The introduction of a PFMMD backbone disrupts the crystallinity of the matrix, increases the matrix free volume, and significantly improves its gas permeability.1 The dioxolane backbone also increases the glass transition temperature of the matrix, impacting its mobility, limiting the ionomer domain swelling and reducing its proton conductivity. I will describe a flexible synthesis method for PFMMD-based ionomers which allowed us to study ionomers with tunable sulfonic acid content and derive structure-property relationships through a combination of transport measurements (i.e., water uptake, proton conductivity, and permeability) and morphological characterization through Small- and Wide-angle X-ray scattering. We will show how the incorporation of dioxolane monomers with bulky, asymmetric side-chains results in a stiff ionomer matrix with distinct chemical and mechanical properties. By varying the dioxolane matrix mass fraction, we gained fundamental insights into the role of the matrix chemical structure on the dynamics of structural and transport processes in ion-conducting polymers.2 Through in situ water uptake measurements, we elucidated the impact of the mass fraction and matrix chemical structure on water sorption rates. The mass-transport swelling rate of Nafion was around 50% higher than in dioxolane-containing ionomers and was independent of the matrix mass fraction. Non-Fickian polymer relaxation rate was sensitive to both type and fraction of the matrix, increasing by 22% across the range of dioxolane fractions studied and by another 100% in Nafion. These effects are attributed to reduction of segmental mobility of the hydrophobic matrix upon incorporation of dioxolane groups. The polymer relaxation is shown to correlate to changes in ionomer conductivity and nanostructure, reveled through in situ Grazing-Incidence Small Angle X-ray Scattering (GISAXS) measurements, showing two distinct physical processes that enable (i) rapid water sorption and ionomer domain swelling and (ii) polymer relaxation and ordering of ionomer domain structure. Lastly, I will discuss the implication and potential utilization of these new materials for improved fuel cell performance. The results presented here underscore the significance of tailoring materials chemistry to specific requirements of fuel cell or electrolysis MEAs.