Ionic Domains Research Articles

Finite Thickness Effects on Nafion Water Uptake and Ionic Conductivity at Hydrophilic Substrate Interfaces, and Implications for PEMFC Performance

Nafion has long been the state-of-the-art solid polymer electrolyte material for a range of next-generation electrochemical energy and chemical separation devices, such as polymer electrolyte membrane fuel cells (PEMFCs). While significant attention over several decades has focused on the polymer structure, proton transport mechanism, and structure-function relationships for bulk membranes, only recently has attention turned to Nafion properties in the catalyst layer (CL), the complex heterogeneous layer where key limiting charge-transfer processes in the PEMFC occur. Recent work suggests that high transport resistance in the CL Nafion contributes to poor PEMFC performance with low Pt loading, but the specific causes of the transport limitations and their implications for PEMFC design are not fully understood. Understanding and quantifying the role of CL Nafion in limiting PEMFC performance is hindered by the complex nano- and micro-structure of the CL – where thin Nafion sheets coat ionomer-flooded agglomerates of carbon-supported Pt catalyst nanoparticles – and by the complex influence of multiple material interfaces and operating conditions on the thin-film Nafion properties. We report here the of dependence of the polymer ionic domain structure and water uptake on the thickness of ultrathin Nafion films (ranging from 5 – 153 nm) coated onto hydrophilic SiO2 substrates, using in situ neutron reflectometry (NR) as a probe. NR is capable of determining structure with sub-Angstrom precision in idealized planar interfaces. Because of isotopic variations in neutron scattering cross sections, it is particularly sensitive to certain elements such as H (and thus water) as well as Li, V, and numerous others. Our results herein show that ionic domains form as sheet-like lamellae at the SiO2 interface, with a thick, bulk-like layer forming at the lamellae/vapor interface for films thicker than 20 nm. The bulk-like layer water uptake increases with increasing thickness for films with equivalent Nafion thickness t Naf < 60 nm, but these bulk-like layers have constant water uptake, similar to bulk 1100 eq. wt. nafion (l = 10) for t Naf ≥ 60 nm. We also show that while the lamellae form due to substrate interactions, their structure and water uptake are also influenced by the presence and composition of the bulk-like layer. Finally, these results indicate that inferring water content from whole-sample measurements (such as swelling or mass uptake measurements) can, in some cases, give an insufficient or even inaccurate measure of the Nafion water uptake. These structural measurements from NR are then used to predict the ionic conductivity of ultrathin Nafion films, using previously established relationships for s ion based on l. Fitting these predictions to experimental data provides evidence of transport limitations in the Nafion film, which increase with increasing proximity to the substrate, and helps to explain previously counter-intuitive trends in ionic conductivity vs. thickness for these films. These effective conductivities are then implemented in numerical simulations of the PEMFC anode and cathode catalyst layers, and demonstrate that both finite thickness effects and sheet-like ionic domain structures at film interfaces can have significant implications for PEMFC performance.

A Study of Carbonate Formation Kinetics and Morphological Effects Observed on OH- Form of Pfaem When Exposed to Air Containing CO2

For AEMFC OH- form of membrane reacts with CO2 when exposed to air leading to loss in conductivity. The data published by Yanagi et.al.[1] suggest that OH species reacts to form Carbonate/bicarbonate in few minutes and after 2 h the membrane only consists of carbonate and bicarbonate. Although this is an important data to consider the reaction kinetics, morphological properties and equilibrium concentrations are still unknown at different environmental conditions. We have attempted to study the CO2 kinetics and its transient effect on conductivity, water-uptake (or lambda) and morphology when the OH- form of PFAEM membrane is exposed to air which has approx. 400 ppm of CO2. The kinetics was studied by exposing the membrane to controlled environment and titrating it using Warder and Winkler titration methods. We have studied transient change in small angle x-ray scattering patterns when the films are exposed to air at different conditions to study the change in d-spacing of the ionic domains. From SAXS analysis it can be concluded that the intensity of spectrum drops over time and the time of equilibration is higher at higher humidity. It takes few hours for the conductivity to drop to carbonate/bicarbonate level. Ultimately we want to understand the effect of CO2 on membrane from every aspect and possibly help us think about strategies to mitigate the problem. Keywords: Anionic exchange membrane, Carbonate,bicarbonate,carbon-dioxide, small angle x-ray scattering Ref: [1]Yanagi and Fukuta, ECS transactions,16(2008). Figure 1

On the electrochemical properties of Mg-PSZ: an overview

MgO-doped partially stabilized zirconia is a complex ceramic electrolyte in which all properties, phase composition, and microstructure are strongly influenced by thermal history besides chemical composition. The electrochemical performance of this ceramic used in oxygen sensors for molten steel is reviewed here. A wide collection of data on electrical properties obtained at various temperatures (up to 1600 °C) and oxygen partial pressures (from 1 atm to values below 10−20 atm) is considered. New aspects are brought to evidence after proper handling of published data on undoped zirconia and MgO-doped materials. The close temperature dependencies of the lower limits of the ionic domains of all these materials suggest the relevance of acceptor-type contaminations on the performance of nominally pure materials. High ionic mobility in the tetragonal phase with respect to the cubic phase is also likely, based on published data. Dopants like Y2O3 originate wider ionic domains but are not equally effective with respect to thermal shock resistance. The unique characteristics of MgO-doped zirconia are due to the coexistence of distinct phases, including large populations of finely dispersed monoclinic and/or tetragonal phases within cubic matrix grains. An overview of key features (materials and design) involved in the performance of oxygen sensors for molten steel is also provided. Typical microstructure of Mg-PSZ with multiple phases and interfaces

Perfluorinated Pyridinium and Imidazolium Ionic Liquids

Ionic liquids with perfluorinated side chains were prepared as hybrid materials for surface impregnation. For the cationic part, methyl and ethyl pyridinium as well as imidazolium scaffolds were used. The anions investigated were hydroxide, acetate, trifluoroacetate, triflate, triflimide, chloride, bromide, iodide, hydrogensulfate, and perfluorododecanoate. A key feature of this investigation is the finding that the use of relatively short perfluorohexyl residues as the fluorinated part of the salts is beneficial for the target compounds compared with established products, because of their lower bioaccumulativity. One compound yielded single crystals that were suitable for X‐ray structure analysis, revealing a layered structure with relatively well‐resolved, hard ionic domains alternating with disordered, soft perfluorinated layers. The wettability of all 30 materials was investigated by water contact angle measurements of a thin film on a glass surface. In two cases, promising contact angles (130° and 140°) were observed, indicating that the products might be suitable candidates for the impregnation of surfaces.

Resilience of Malic Acid Natural Deep Eutectic Solvent Nanostructure to Solidification and Hydration.

Little is presently known about the unique nanostructure of deep eutectic solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using empirical potential structure refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD) contribution. The 1:1 eutectic stoichiometry makes these ionic domains more well-defined, with less HBD clustering than seen previously for reline. There is minimal structural difference for the solidified material, demonstrating that this DES solidification is a glass transition rather than a first order phase change. QENS data support this by showing a gradual change in solvent dynamics rather than a step change. The DES structure is mostly retained upon hydration, with water acting both as a secondary smaller HBD at closer range to choline than malic acid, and forming transient wormlike aggregates. This new understanding of DES structure will aid understanding of the properties of these novel green solvents on the molecular length scale in chemical processes, as well as giving an insight into the apparent role of natural DESs in plant physiology.

Proton Transport in Hierarchical-Structured Nafion Membranes: A NMR Study.

It is known that hierarchical structure plays a key role in many unique material properties such as self-cleaning effect of lotus leaves and the antifogging property of the compound eyes of mosquitoes. This study reports a series of highly ordered mesoporous Nafion membranes with unique hierarchical structural features at the nanometer scale. Using NMR, we show for the first time that, at low RH conditions, the proton in the ionic domains migrates via a surface diffusion mechanism and exhibits approximately 2 orders of magnitude faster transport than that in the nanopores, whereas the nanopores play a role of reservoir and maintain water and thereby conductivity at higher temperature and lower humidities. Thereby creating hierarchical nanoscale structures is a feasible and promising strategy to develop PEMs that would enable efficient electrochemical performance in devices such as fuel cells, even in the absence of high humidity and at elevated temperatures.

21pPSA-40 中性相TTF-CAにおけるイオン性相ドメインの量子揺らぎ : 断熱近似を超えた量子論的アプローチ

21pPSA-40 中性相TTF-CAにおけるイオン性相ドメインの量子揺らぎ : 断熱近似を超えた量子論的アプローチ

Synthesis and properties of quaternized polyolefins with bulky poly(4-phenyl-1-butene) moieties as anion exchange membranes

Polyolefin-based anion exchange membranes (AEMs) with well-defined ionic domains for anion transport were synthesized by introducing bulky poly(4-phenyl-1-butene) (P4PB) moieties into quaternized polyolefinic copolymers via heterogeneous catalytic copolymerization of 4-phenyl-1-butene with 11-bromo-1-undecene over a Ziegler–Natta catalyst and subsequent quaternization. Well-defined hydrophobic-hydrophilic separation was observed for the as-obtained membranes, as confirmed by atomic force microscopy (AFM). The membranes showed high hydroxide conductivity (10.4mScm−1) despite their low ion exchange capacity (IEC, 0.98meqg−1). When compared with membranes containing poly(4-methyl-1-pentene) (PMP) or polypropylene (PP) moieties, the membranes obtained herein showed lower conductivities under similar conditions at IEC values higher than 1.2meqg−1. Excessive swelling of the P4PB membranes resulting from a high water uptake (WU) was assumed to decrease the ion concentration in the membrane. Thus, lower volumetric IEC values were observed for AEMs with IEC higher than 1.2meqg−1. A maximum hydroxide conductivity of 18.9mScm−1 at room temperature was obtained for the P4PB-TMA-43 membrane (IEC = 2.17meqg−1, WU = 262.4wt%). Similar to our previous report on polyolefin-based AEMs with PMP or PP moieties, side chains with nine methylene units between the polymer backbone and the quaternary ammonium (QA) cations were very stable and showed no apparent degradation upon storage in a 10M NaOH aqueous solution at 80°C for 20d. We demonstrated that a polyolefin-based molecular architecture combined with poly-QA side chains attached via flexible spacer units with bulky side chain moieties achieved AEMs with efficient phase separation and high alkaline stability characteristics.

Crosslinked side-chain-type anion exchange membranes with enhanced conductivity and dimensional stability

Covalent crosslinking is considered to be a promising strategy to balance the dimensional stability and conductivity of anion exchange membranes (AEMs). Nevertheless, crosslinking using diamine crosslinkers would introduce hydrophobic alkyl chains into the ionic domain resulting in a significant decline in hydroxide conductivity and crosslinking via catalyst is discouraged. Herein, we presented a strategy for preparing crosslinked AEMs without using catalyst and the crosslinked moiety is away from the ionic domain. The crosslinking was carried out by converting the trifluorovinyl groups into perfluorocyclobutane groups via thermal treatment. The designed side-chain structure is responsible for the obvious hydrophilic/hydrophobic phase separated morphology and interconnected ion conducting channels, as confirmed by atomic force microscopy, transmission electron microscopy and small angle X-ray scattering. The obtained membrane exhibited high dimensional stability and a highest conductivity of 77.1mScm−1 at 80°C. Furthermore, the crosslinked AEMs also had robust mechanical properties, good thermal stability and reasonable alkaline stability.

Analysis of Prepeak Structure of Concentrated Organic Lithium Electrolyte by Means of Neutron Diffraction with Isotopic Substitution and Molecular Dynamics Simulation.

The prepeak structure of a 3 mol/kg solution of LiClO4 in propylene carbonate (PC) was studied by both neutron diffraction with isotopic substitution (NDIS) and molecular dynamics (MD) simulation. The NDIS data showed that the intensity of the prepeak decreases experimentally with an increase in the scattering length of the lithium atom from 7Li to 6Li in PC-d6. On the other hand, although the prepeak was observed in solutions of both PC-d6 and PC-h6, it disappears when the 1:1 mixture of PC-d6 and PC-h6 was used as the solvent. The prepeak structure and its variation with the isotope substitution were reproduced well by MD simulation, and they were explained in terms of the contrast of the scattering length densities of the ionic and nonpolar domains.

Computational perspectives on structure, dynamics, gas sorption, and bio-interactions in deep eutectic solvents

We present a snapshot of the current status of understanding structure, dynamics, and molecular interactions within deep eutectic solvents (DESs) gained from a computational perspective. The simulations reported thus far have been largely aimed at unravelling the relationship between the molecular features within a DES and the depressed melting temperature at its eutectic composition. Computational efforts consistently reveal that the addition of hydrogen bond donors significantly disrupts long-range ordering of the cation–anion arrangement in choline chloride, resulting in significant moderation of the interaction energies between the components of the DES. These studies paint a picture of DES formation being accompanied by hydrogen-bond directed charge transfer processes yielding transient cage-like formation and nanoscale ordering entailing segregation of the ionic and molecular domains. Computational insights further uncover how unique solvation features present within DESs may lead to enhanced biomolecular (e.g., protein, nucleic acid, polysaccharide) stability and/or activity while also offering advantages as environmentally-responsible gas sorbents.

Effects of Block Ionomer Morphologies on the Electromechanical Performance of Ionomeric Polymer-Metal Composite Actuators

Ionomeric polymer-metal composites (IPMCs), which is a type of electroactive polymers, can generate a large and fast bending actuation under a low operating voltage (1~5V) (1). This superior electromechanical performance, combined with the inherent nature of polymer such as lightweight and softness, makes them attractive for biomimetic devices such as artificial muscles and soft robots (2). IPMCs have a tri-layer structure that consists of an ionomer film incorporating ions and water (or ionic liquids), and electrodes plated on both film surfaces (1-4). Upon applying a voltage, water and ions move toward the oppositely charged side leading to unsymmetrical polymer swelling. This change is restrained within the polymer’s nonionic matrix resulting in asymmetric stress that drives the bending motion. Advanced electromechanical performance of IPMCs relies on the ion and water transport ability and mechanical integrity of the used ionomer (3-5). In this work, the electromechanical performance of water-based IPMC actuators was examined as a function of the phase-separated morphology of a sulfonated penta-block ionomer (SBI). The SBI films---cast from a range of nonpolar/polar solvent blends---had a series of morphologies varied from poorly-connected ionic domains to well-connected lamellar/hexagonal structures. The poorly-connected structure led to a slow and small actuating response due to the small through-plane ion conductivity (1.5 mS/cm) and water permeability (1.3 × 10-6 mm2/(s MPa)). The SBI film with the lamellar/hexagonal structure however had an excessive water uptake (46wt. %) that greatly impaired the mechanical strength (53 MPa). The IPMC made from this film showed a faster and larger bending over the poorly-connected one but lost the advantage in terms of bending strain energy density. Interestingly, the best-performing IPMC is a SBI film possessing a lamella-like structure with its ionic domains perforated by nonionic polymer matrix. Its superior performance in terms of both bending displacement and strain energy density was attributed to the simultaneous improvements of ion and water transport (19.6 mS/cm and 3.1 × 10-5 mm2/(s MPa), respectively), and mechanical properties (125 MPa). Consequently, an optimal morphology exists for ideal electromechanical performance that is linked to molecule transport and ionomer mechanical properties. (1) Shahinpoor, M.; Kim, K. J. Ionic Polymer – Metal Composites : I .Fundemental. Smart Mater. Struct. 2001, 10, 819-833. (2) Shahinpoor, M.; Kim, K. J. Ionic Polymer–metal Composites: IV. Industrial and Medical Applications. Smart Mater. Struct. 2005, 14 (1), 197–214. (3) Nemat-Nasser, S. Micromechanics of Actuation of Ionic Polymer-Metal Composites. J. Appl. Phys. 2002, 92 (5), 2899–2915. (4) Asaka, K.; Oguro, K. Bending of Polyelectrolyte Membrane Platinum Composites by Electric Stimuli PartII. Response Kinetics. J. Electroanal. Chem. 2000, 480, 186–198. (5) Zhu, Z.; Asaka, K.; Chang, L.; Takagi, K.; Chen, H. Multiphysics of Ionic Polymer–metal Composite Actuator. J. Appl. Phys. 2013, 114 (8), 084902. Figure 1

Ion Transport in Single-Ion Conducting Polymer Electrolytes for Lithium Batteries

Electrochemical energy storage devices are increasingly desired for consumer vehicle electrification and renewable power utilization. Safety and performance of batteries is strongly dictated by the performance of the electrolyte. Polymer electrolytes offer advantages over liquid and inorganic solid-state electrolytes, as they are non-leakable and non-volatile, yet flexible. Single-ion conducting electrolytes that eliminate ion concentration gradients offer further advantages: greater electrochemical stability allowing for higher voltage cells, lower interfacial impedance, and higher theoretical charge/discharge rates. Single-ion conducting polymer electrolytes may simply be created by titration of an ionomer with the active ion – Li+ in a Li-ion battery, for example. Unfortunately, the drastically low ionic conductivity of single-ion conducting polymer electrolytes without added solvent has precluded their commercial application thus far. Improved understanding of lithium ion transport mechanisms is critical for the development of high performance electrolytes. Our efforts in this area are focused on understanding ion states and ion transport in two distinct classes of single-ion conducting polymers. The first class of materials of interest are polyethers with highly dissociable tethered anions, where the research focus is to understand ion-pair dissociation and ion states that contribute to conduction. The second class of materials of interest are ionomers with solely non-polar polymer components, where we aim to understand ion transport through ionic domains.

Pentablock Ionomer Based TEOS-TIP Hybrid Nanocomposites: Morphology, Physical Properties, and Ion Transport

Nowadays, pure materials cannot embody all the physical, chemical, and mechanical properties required for a given application. Therefore, hybrid inorganic-organic composite materials were created to fill this critical void. The hybrid composites depend not only the properties of individual components, but also on the interfacial interactions between inorganic and organic phases. The significance of this work is to control the interaction-structure-property relationships of hybrid inorganic-organic nanocomposites in many applications such as fuel cells, lithium-ion batteries, biomimetic actuator, and water purification. The PBC based hybrid organic-inorganic films were synthesized based on tetraethylorthosilicate (TEOS), titanium isopropoxide (TIP), and poly(t-butylstyrene-b-hydrogenated isoprene-b-sulfonated styrene-b-hydrogenated isoprene-b-t-butylstyrene) or pentablock copolymer (PBC) via sol-gel chemistry. A ternary phase diagram was estibalished to understand the homogeneity of TEOS-TIP sol-gel system dependent on initial sol composition and reaction conditions leading to controllable materials. All hybrid PBC-TEOS-TIP membranes exhibited higher water uptake than unmodified PBC membranes. Proton conductivity increased 80% from 58 mS/cm for unmodified PBC film to 85 mS/cm for hybrid nanocomposite film due to the role TEOS-TIP within it. This can be attributed to the partial charge transfer from the titanate’s inorganic domains to sulfonate groups that promote acid dissociation and proton attraction. The PBC’s microphase-separated morphology changed from well-ordered lamella-like structure to a random and homogenous distribution of ionic domains with increasing TIP concentration, which was observed from AFM and SAXS results. TGA analyses revealed a decrease in degradation temperature due to titanate's catalytic character, and DMA results demonstrated reduced polymer chain mobility caused by inorganic-organic interactions. Finally, these PBC-TEOS-TIP hybrid composites were used as proton-exchange membranes (PEM) for hygroden fuel cells.

Simultaneous wastewater treatment and bioelectricity production in microbial fuel cells using cross-linked chitosan-graphene oxide mixed-matrix membranes.

Microbial fuel cells (MFCs) are emerging technology for wastewater treatment by chemical oxygen demand (COD) reduction and simultaneous bioelectricity production. Fabrication of an effective proton exchange membrane (PEM) is a vital component for MFC performance. In this work, green chitosan-based (CS) PEMs were fabricated with graphene oxide (GO) as filler material (CS-GO) and cross-linked with phosphoric acid (CS-GO-P(24)) or sulfuric acid (CS-GO-S(24)) to determine their effect on PEM properties. Interrogation of the physicochemical, thermal, and mechanical properties of the cross-linked CS-GO PEMs demonstrated that ionic cross-linking based on the incorporation of PO43- groups in the CS-GO mixed-matrix composites, when compared with sulfuric acid cross-linking commonly used in proton exchange membrane fuel cell (PEMFC) studies, generated additional density of ionic cluster domains, rendered enhanced sorption properties, and augmented the thermal and mechanical stability of the composite structure. Consequently, bioelectricity performance analysis in MFC application showed that CS-GO-P(24) membrane produced 135% higher power density than the CS-GO-S(24) MFC system. Simultaneously, 89.52% COD removal of primary clarifier municipal wastewater was achieved in the MFC operated with the CS-GO-P(24) membrane.

Terahertz-Field-Induced Large Macroscopic Polarization and Domain-Wall Dynamics in an Organic Molecular Dielectric.

A rapid polarization control in paraelectric materials is important for an ultrafast optical switching useful in the future optical communication. In this study, we applied terahertz-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopies to the paraelectric neutral phase of an organic molecular dielectric, tetrathiafulvalene-p-chloranil and revealed that a terahertz pulse with the electric-field amplitude of ∼400 kV/cm produces in the subpicosecond time scale a large macroscopic polarization whose magnitude reaches ∼20% of that in the ferroelectric ionic phase. Such a large polarization generation is attributed to the intermolecular charge transfers and breathing motions of domain walls between microscopic neutral and ionic domains induced by the terahertz electric field.

Graphene Visualizes the Ion Distribution on Air-Cleaved Mica

The distribution of potassium (K+) ions on air-cleaved mica is important in many interfacial phenomena such as crystal growth, self-assembly and charge transfer on mica. However, due to experimental limitations to nondestructively probe single ions and ionic domains, their exact lateral organization is yet unknown. We show, by the use of graphene as an ultra-thin protective coating and scanning probe microscopies, that single potassium ions form ordered structures that are covered by an ice layer. The K+ ions prefer to minimize the number of nearest neighbour K+ ions by forming row-like structures as well as small domains. This trend is a result of repulsive ionic forces between adjacent ions, weakened due to screening by the surrounding water molecules. Using high resolution conductive atomic force microscopy maps, the local conductance of the graphene is measured, revealing a direct correlation between the K+ distribution and the structure of the ice layer. Our results shed light on the local distribution of ions on the air-cleaved mica, solving a long-standing enigma. They also provide a detailed understanding of charge transfer from the ionic domains towards graphene.

Imidazolium ionic liquid incorporation on sulfonated poly(styrene‐isobutylene‐styrene) proton exchange membranes

ABSTRACTIonic liquids (ILs) with different anions and cations were incorporated in sulfonated poly(styrene‐isobutylene‐styrene) (SIBS) to modify its chemical, morphological, and transport properties for direct methanol fuel cell (DMFC) applications. Different loadings of IL and different solvents were studied to have a better understanding of the incorporation process and the ability of the solvent to affect the interaction of the IL with the sulfonated polymer. Morphological characterization with SAXS and AFM suggested changes caused by the incorporation of the IL and by the solvent used. FT‐IR spectra showed small variations in energy related to interactions of the IL with the sulfonic groups which caused thermogravimetric stabilization of the ionic domains. Other results suggest that water has a very significant effect on the morphology, interaction with the IL, and transport properties of the membranes. Optimal concentration of IL (∼10 mol %) provides enough water to produce efficient proton conductivity (0.15 S/cm) and minimal methanol permeability (0.8 × 10−6 cm2/s). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44900.

Ion transport properties of mechanically stable symmetric ABCBA pentablock copolymers with quaternary ammonium functionalized midblock

ABSTRACTAnion exchange membranes (AEMs) are a promising class of materials for applications that require selective ion transport, such as fuel cells, water purification, and electrolysis devices. Studies of structure–morphology–property relationships of ion‐exchange membranes revealed that block copolymers exhibit improved ion conductivity and mechanical properties due to their microphase‐separated morphologies with well‐defined ionic domains. While most studies focused on symmetric diblock or triblock copolymers, here, the first example of a midblock quaternized pentablock AEM is presented. A symmetric ABCBA pentablock copolymer was functionalized to obtain a midblock brominated polymer. Solution cast films were then quaternized to obtain AEMs with resulting ion exchange capacities (IEC) ranging from 0.4 to 0.9 mmol/g. Despite the relatively low IEC, the polymers were highly conductive (up to 60 mS/cm Br− at 90 °C and 95%RH) with low water absorption (&lt;25 wt %) and maintained adequate mechanical properties in both dry and hydrated conditions. X‐ray scattering and transmission electron microscopy (TEM) revealed formation of cylindrical non‐ionic domains in a connected ionic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 612–622

Effect of block composition on the morphology and transport properties of sulfonated fluoroblock copolymer blend membranes

This study focuses on the relationship between the transport properties and the morphological changes of ionic block copolymer blend membranes, as a function of the fluoroblock chemical composition and loading. Poly(styrene‐b‐isobutylene‐b‐styrene) was sulfonated and blended with three different fluoropolymers: Poly(styrene)‐b‐poly(2,3,4,5,6‐pentafluorostyrene)‐b‐poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate) [PS‐b‐PFS‐b‐PHFBMA], a difluoroblock copolymer composed of PS‐b‐PHFBMA and a homopolymer composed of PHFBMA. Equilibrium and transport properties (e.g., ion exchange capacity, water uptake, water content, proton conductivity, and methanol permeability), were shown to be significantly influenced by the chemical nature of the fluoroblock copolymer, the fluoropolymer content, and their resulting morphology. Proton conductivity and methanol permeability were very sensitive to the incorporation of PHFBMA. Polymer blends composed of sulfonated poly(styrene‐b‐isobutylene‐b‐styrene) (SIBS SO3H) and PHFBMA above 9 wt% showed interconnected ionic domains that have a shorter correlation length and high water content, which results in improved transport properties for direct methanol fuel cell (DMFC) applications. POLYM. ENG. SCI., 57:1262–1272, 2017. © 2017 Society of Plastics Engineers