High proton conductivity of water channels in a highly ordered nanowire

A proton-conductive material based on a crystalline assembly of trimesic acid and melamine (TMA?M, see picture) is reported. Because of the ordered structure of the assembly, the water-saturated proton conductivity for the TMA?M assembly is 5.5?S?cm(-1) , which is the highest proton conductivity measured to date. This exceptionally high conductivity and low-cost fabrication of the material make applications feasible for fuel-cell devices.     

Effects of water nanochannel diameter on proton transport in proton‐exchange membranes

The effects of water nanochannel diameter on proton transport pathways and properties have been studied using reactive molecular dynamics simulations. The proton distributions and diffusivities have been evaluated using the cylinder model of water domains at various diameters that is the most typical proposed morphological model in proton‐exchange membranes. The proton distributions are analyzed to clarify proton pathways by classifying the water channel into two regions in parallel: an inner channel (free water) and an outer channel (bound water). For all the water contents, the nonmonotonic trends that show a peak at a certain diameter are found to be observed in the proton diffusivity, which is dominated by the proton diffusivity in the free water region and has a strong correlation with the proton distribution that is controlled by the balance between the volume fraction of free water and the surface density of sulfonate groups. The electroosmotic drag coefficients are found to increase monotonically with increasing channel diameter as a result of the increase in the volume fraction of free water. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 867–878     

Predicting the Morphology of Metallo‐Supramolecular Block Copolymers with Bulky Counter Ions

Summary: The phase behavior of metallo‐supramolecular block copolymers with bulky counter ions is theoretically studied within the framework of a mean‐field dynamic density functional theory and compared with recent experiments on a polystyrene–poly(ethylene oxide) metallo‐supramolecular diblock copolymer, PS₂₀‐[Ru]‐PEO₇₀, with tetraphenylborate counter ions. The copolymer is modeled as a triblock polyelectrolyte, in which the metal complex is treated as the polyelectrolyte block. The topology and kinetics of the formation of the observed three‐domain lamellar morphology in which the polyelectrolyte blocks and bulky counter ions are located together to form electroneutral complexes, are in good agreement with experimental results. In addition, the model predicts the existence of core–shell morphologies. The agreement with and variations from the experimental phase diagram are discussed in detail.

Morphological transformations in a metallo‐supramolecular block copolymer with bulky counter ions upon increasing the temperature.     

Synthesis and characterization of sulfonated‐fluorinated,hydrophilic‐hydrophobic multiblock copolymers for proton exchange membranes

Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. These copolymers were obtained through moderate temperature (～ 100 °C) coupling reactions, which minimize the ether‐ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3′‐disulfonated, 4,4′‐dichlorodiphenyl sulfone with an excess 4,4′‐biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure‐property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self‐assembly of the sulfonated blocks. The nano‐phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state‐of‐the‐art PEM, Nafion, were achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1038–1051, 2009     

Synthesis and characterization of multiblock partially fluorinated hydrophobic poly(arylene ether sulfone)‐hydrophilic disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes

Hydrophobic‐hydrophilic sequence multiblock copolymers, based on alternating segments of phenoxide terminated fully disulfonated poly(arylene ether sulfone) (BPS100) and fluorine‐terminated poly(arylene ether sulfone) (6FBPS0) were synthesized and evaluated for application as proton exchange membranes. By utilizing mild reaction conditions the ether–ether interchange reactions were minimized, preventing the randomization of the multiblock copolymers. Tough, ductile, transparent membranes were solution cast from the block copolymers and were characterized with regard to intrinsic viscosity, morphology, water uptake, and proton conductivity. The conductivity values of the 6FBPS0‐BPSH100 membranes were compared to Nafion 212 and a partially fluorinated sulfonated poly(arylene ether sulfone) random copolymer (6F40BP60). The nanophase separated morphology was confirmed by transmission electron microscopy and small angle X‐ray scattering, and enhanced proton conductivity at reduced relative humidity was observed with longer block lengths. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Polyelectrolyte micelles in salt‐free solutions: Micelle size and electrostatic potential

The structural and electrical characteristics of polyelectrolyte micelles formed by diblock copolymers with one charged block and one solvophobic block are studied by the means of molecular dynamics simulations using the Primitive model at different Bjerrum lengths. The properties of interest are the mean aggregation number, the shape, the electrical potential as a function of the distance of the micelle's center of mass and the zeta potential. We found that for partially charged short A blocks the micelles’ mass distribution function is at least bimodal, indicating the coexistence of small and large micelles in agreement with theoretical and experimental findings. The zeta potential is not a monotonic function of the length of the charged block. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 924–934     

Synthesis of poly(arylene ether sulfone)‐block‐sulfonated polybutadiene: the selective post‐sulfonation of block copolymers as proton exchange membranes

A series of poly(arylene ether sulfone)‐block‐sulfonated polybutadiene (PAES‐b‐sPB) with different ion exchange capacities (IECs) were synthesized and evaluated as proton exchange membranes (PEMs) for possible applications in fuel cells. These sulfonated block copolymers were synthesized via condensation reaction between modified PAES and PB prepolymers, followed by selective post‐sulfonation of PB blocks using acetyl sulfate as the sulfonating reagent. The sulfonic groups were only attached onto PB blocks due to the high reactivity of double bonds to acetyl sulfate. The success of synthesis and selective post‐sulfonation were all confirmed by the Fourier transform infrared (FT‐IR) and nuclear magnetic resonance (NMR) spectra. PAES‐b‐sPB had good film‐forming ability and thermal stability. Mechanical properties of membranes varied with the sulfonation. The presence of sulfonic groups increased the tensile strength and Young's modulus but decreased the elongation at break. Transmission electron microscopy (TEM) images showed large ionic aggregates in membranes. Phase separation as well as the interconnected sulfonate groups which only localized on flexible PB blocks led to these ionic domains. The proton conductivity increased with the increasing IEC and temperature. With relatively low IEC, most membranes still exhibited sufficient proton conductivity. The above results indicated this strategy could be a prospective choice to prepare novel PEMs. Copyright © 2010 John Wiley & Sons, Ltd.     

Polymer electrolyte membranes based on p‐toluenesulfonic acid doped poly(1‐vinyl‐1,2,4‐triazole): Synthesis,thermal and proton conductivity properties

Throughout this work, the synthesis, thermal as well as proton conducting properties of acid doped heterocyclic polymer were studied under anhydrous conditions. In this context, poly(1‐vinyl‐1,2,4‐triazole), PVTri was produced by free radical polymerization of 1‐vinyl‐1,2,4‐triazole with a high yield. The structure of the homopolymer was proved by FTIR and solid state ¹³C CP‐MAS NMR spectroscopy. The polymer was doped with p‐toluenesulfonic acid at various molar ratios, x = 0.5, 1, 1.5, 2, with respect to polymer repeating unit. The proton transfer from p‐toluenesulfonic acid to the triazole rings was proved with FTIR spectroscopy. Thermogravimetry analysis showed that the samples are thermally stable up to ～250 °C. Differential scanning calorimetry results illustrated that the materials are homogeneous and the dopant strongly affects the glass transition temperature of the host polymer. Cyclic voltammetry results showed that the electrochemical stability domain extends over 3 V. The proton conductivity of these materials increased with dopant concentration and the temperature. Charge transport relaxation times were derived via complex electrical modulus formalism (M*). The temperature dependence of conductivity relaxation times showed that the proton conductivity occurs via structure diffusion. In the anhydrous state, the proton conductivity of PVTri1PTSA and PVTri2PTSA was measured as 8 × 10^?4 S/cm at 150 °C and 0.012 S/cm at 110 °C, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1016–1021, 2010     

Probing microphase separation and proton transport cooperativity in polymer‐tethered 1H‐tetrazoles

To elucidate the driving forces for phase separation and proton conductivity in polystyrenic alkoxy 1H‐tetrazole (PS‐Tet), an analogous polystyrenic alkoxy carboxylic acid (PS‐HA) was synthesized and the conductivity and chain dynamics of both materials measured. Proton and polymer motions illustrate dramatic differences in the nonaqueous behavior of carboxylic acids and 1H‐tetrazoles, belying similarities in their aqueous properties. Exceptional interactions between 1H‐tetrazoles drive phase separation not observed in PS‐HA or reported for other azole‐containing homopolymers. PS‐HA and PS‐Tet exhibit both dry (0% relative humidity) and hydrated proton dissociations proportional to their aqueous pK_as, with residual water acting as the proton acceptor in both polymers. While water is the sole contributor to mobility in PS‐HA, PS‐Tet exhibits dynamic interactions with water allowing 1H‐tetrazole moieties to contribute to proton conduction even in the hydrated state. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1375–1387     

Preparation and characterization of PVDF‐based blend membranes as polymer electrolyte membranes in fuel cells: Study of factor affecting the proton conductivity behavior

There is a huge demand especially for polyvinylidene fluoride (PVDF) and its copolymers to provide high performance solid polymer electrolytes for use as an electrolyte in energy supply systems. In this regard, the blending approach was used to prepare PVDF‐based proton exchange membranes and focused on the study of factor affecting the ir proton conductivity behavior. Thus, a series of copolymers consisting of poly (methyl methacrylate) (PMMA), polyacrylonitrile (PAN), and poly(2‐acrylamido‐2‐methyl‐l‐propanesulfonic acid) (PAMPS) as sulfonated segments were synthesized and blended with PVDF matrix in order to create proton transport sites in PVDF matrix. It was found that addition of PMMA‐co‐PAMPS and PAN‐co‐PAMPS copolymers resulted in a significant increase in porosity, which favored the water uptake and proton transport at ambient temperature. Furthermore, crystallinity degree of the PVDF‐based blend membranes was increased by addition of the related copolymers, which is mainly attributed to formation of hydrogen bonding interaction between PVDF matrix and the synthesized copolymers, and led to a slight decrease in proton conductivity behavior of blend membranes. From impedance data, the proton conductivity of the PVDF/PMMA‐co‐PAMPS and PVDF/PAN‐co‐PAMPS blend membranes increases to 10 and 8.4 mS cm⁻¹ by adding only 50% of the related copolymer (at 25°C), respectively. Also, the blend membranes containing 30% sulfonated copolymers showed a power density as high as 34.30 and 30.10 mW cm⁻² at peak current density of 140 and 79.45 mA cm⁻² for the PVDF/PMMA‐co‐PAMPS and PVDF/PAN‐co‐PAMPS blend membranes, respectively. A reduction in the tensile strength was observed by the addition of amphiphilic copolymer, whereas the elongation at break of all blend membranes was raised.     

Fluorophilic cobalt phthalocyanine‐containing Nafion membrane: high oxygen permeability and proton conductivity in the membrane

A multiply‐fluorinated cobalt phthalocyanine (CoFPC) was prepared, which could reversibly interact with oxygen. CoFPC was introduced into the hydrophobic perfluoroethylene‐backbone domain of the Nafion membrane. The localization of CoFPC did not reduce the high proton conductivity (10^?2–10^?3 S cm^?1) ascribed to the hydrophilic channel of Nafion. The oxygen permeability through the CoFPC/Nafion membrane was higher than the nitrogen permeability and that of the pristine Nafion membrane, and was significantly enhanced at the lower upstream pressure. The permselectivity of oxygen versus nitrogen increased beyond 20 with the CoFPC content in the membrane. The CoFPC/Nafion membrane was coated on a glassy carbon modified with a Pt/C catalyst. The high electrochemical reduction current of oxygen suggested that the CoFPC/Nafion membrane efficiently supplied oxygen to the Pt/C catalyst. Copyright © 2009 John Wiley & Sons, Ltd.     

Hybridization of Nafion membranes with an acid functionalised polysiloxane: Effect of morphology on water sorption and proton conductivity

Polysiloxane-modified hybrid Nafion membranes were prepared by casting a mixture of Nafion solution and a precursor of acid functionalised polysiloxane based on tetraethoxysilane and a mercaptan-organoalkoxysilane.Scanning Electron Microscopy (SEM) and Atomic Force Microscopy analysis revealed that the functionalised polysiloxane was dispersed either as finely nanosized inclusions or as coarse domains depending on the rate of the solvent evaporation during the casting procedure. In particular the slower is the rate of solvent evaporation the more interpenetrated and homogenously dispersed at nanosized level is the polysiloxane inside the Nafion membrane.The hybridization process increases the thermal stability of the membranes of about 50 °C relatively to the unmodified Nafion. Small angle X-ray scattering (SAXS) analysis reveals that the hybrid membranes exhibited the typical morphology of Nafion consisting of distinct hydrophilic and hydrophobic domains.Water vapor sorption and proton conductivity were measured varying the temperature (up to 120 °C) and the water activity conditions (from 0.1 to 0.8). The polysiloxane network always increases the water vapor uptake of the membranes and increases significantly the proton conductivity at higher temperature depending on the type of morphology developed by the manufacturing method. In particular hybrid membranes exhibiting nanosized polysiloxane dispersion show a proton conductivity which is up to one-and-half time higher than Nafion recast membrane at high temperature and low water content.     

Highly proton conducting proton‐exchange membranes based on fluorinated poly(arylene ether ketone)s with octasulfonated segments

A new bisphenol monomer containing a pair of electron‐rich tetra‐arylmethane units was designed and synthesized. Based on this monomer, along with commercial 4,4′‐(hexafluoroisopropylidene)diphenol A and 4,4′‐difluorobenzophenone, a series of novel poly(arylene ether ketone)s containing octasulfonated segments of varying molar percentage (x) (6F‐SPAEK‐x) were successfully synthesized by polycondensation reactions, followed by sulfonation. Tough, flexible, and transparent membranes, exhibiting excellent thermal stabilities and mechanical properties were obtained by casting. 6F‐SPAEK‐x samples exhibited appropriate water uptake and swelling ratios at moderate ion exchange capacities (IECs) and excellent proton conductivities. The highest proton conductivity (215 mS cm⁻¹) is observed for hydrated 6F‐SPAEK‐15 (IEC = 1.68 meq g⁻¹) at 100 °C, which is more than 1.5 times that of Nafion 117. Furthermore, the 6F‐SPAEK‐10 membrane exhibited comparable proton conductivity (102 mS cm⁻¹) to that of Nafion 117 at 80 °C, with a relatively low IEC value (1.26 meq g⁻¹). Even under 30% relative humidity, the 6F‐SPAEK‐20 membrane (2.06 meq g⁻¹) showed adequate conductivity (2.1 mS cm⁻¹) compared with Nafion 117 (3.4 mS cm⁻¹). The excellent comprehensive properties of these membranes are attributed to well‐defined nanophase‐separated structures promoted by strong polarity differences between highly ionized and fluorinated hydrophobic segments. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 25–37     

Surface Phase Separation and Morphology of Stimuli Responsive Complex Micelles

Complex micelles with a P4VP core surrounded by a mixed PNIPAM/PEG shell were prepared by comicellization of PNIPAM₉₃‐b‐P4VP₅₈ and PEG₁₁₄‐b‐P4VP₅₈ in aqueous solutions. Increasing the temperature above the LCST of the PNIPAM induced a phase separation of the mixed shell due to the collapse of the PNIPAM block. The morphology of the collapsed PNIPAM was dependent on the composition of the mixed shell; a lower content of the PNIPAM resulted in separately distributed domains on the surface of the P4VP core, while a higher content of the PNIPAM led to the formation of continuous membrane around the P4VP core. When the continuous membrane was formed, the hydrophilic PEG block could connect the inner P4VP core and the outer milieu to form channels across the PNIPAM membrane for water and other small molecules to pass through.

     

Multistate empirical valence bond study of temperature and confinement effects on proton transfer in water inside hydrophobic nanochannels

Microscopic characteristics of an aqueous excess proton in a wide range of thermodynamic states, from low density amorphous ices (down to 100 K) to high temperature liquids under the critical point (up to 600 K), placed inside hydrophobic graphene slabs at the nanometric scale (with interplate distances between 3.1 and 0.7 nm wide) have been analyzed by means of molecular dynamics simulations. Water‐proton and carbon‐proton forces were modeled with a multistate empirical valence bond method. Densities between 0.07 and 0.02 Å^?3 have been considered. As a general trend, we observed a competition between effects of confinement and temperature on structure and dynamical properties of the lone proton. Confinement has strong influence on the local structure of the proton, whereas the main effect of temperature on proton properties is observed on its dynamics, with significant variation of proton transfer rates, proton diffusion coefficients, and characteristic frequencies of vibrational motions. Proton transfer is an activated process with energy barriers between 1 and 10 kJ/mol for both proton transfer and diffusion, depending of the temperature range considered and also on the interplate distance. Arrhenius‐like behavior of the transfer rates and of proton diffusion are clearly observed for states above 100 K. Spectral densities of proton species indicated that in all states Zundel‐like and Eigen‐like complexes survive at some extent. © 2016 Wiley Periodicals, Inc.     

Crosslinking effects on hybrid organic–inorganic proton conducting membranes based on sulfonated polystyrene and polysiloxane

New hybrid semi‐interpenetrating proton‐conducting membranes were obtained using sulfonated polystyrene (SPS) and inorganic–organic polysiloxane phases with the aim of improving the mechanical and thermal characteristics of the pristine polymer and to study the effects of crosslinking in the latter phase in several of their properties, mainly proton conductivity. Siloxane phases were prepared using poly(dimethylsiloxane) (PDMS) and PDMS with tetraethoxysilane (TEOS) or phenyltrimethoxysilane (PTMS) as crosslinking agents. To study the crosslinking effect, membranes were prepared with different TEOS:PDMS and PTMS:PDMS mole ratios. The films obtained were characterized by FTIR, ²⁹Si‐HPDEC MAS‐NMR, ¹³C‐CP‐MAS NMR, elemental and thermal analyses. Certain properties, such as water uptake (WU), ion exchange capacity (IEC) and the state of the water, were determined. The proton conductivity was measured at different temperatures (30°C and 80°C) and relative humidities (50–95%). The water content of the hybrid membranes declined significantly, compared with the SPS membranes, depending on the nature and amount of siloxane phase added. Nonetheless, the conductivity values remained relatively high (>100 mS cm^?1 at 80°C and 95% RH) when compared to Nafion®117 presumably because of the formation of well developed proton channels, which makes them potentially promising as proton exchange membranes for fuel cells. These membranes proved to be thermally stable up to 350°C. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) were used to characterize the hybrid membranes microstructures; the latter provided contrast for the conductive domains. Copyright © 2015 John Wiley & Sons, Ltd.     

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

Fully atomistic molecular dynamics simulations of poly(2‐[2‐methoxyethoxy]ethyl methacrylate) (PMEO₂MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO₂MA undergo a distinct coil‐to‐globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO₂MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage‐like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water‐ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)‐based homopolymers at atomistic level that will be useful when designing homo‐ and co‐polymers of OEGMAs with desired properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 429–441     

Molecular dynamics study of the cations,water molecules,and polymer chains in Nafion type membranes

The structure and dynamics of the hydrated cationic complexes in Nafion type membrane pores has been studied by the molecular dynamics approach. The mechanism of the cationic transport has been examined. The dependence of the cationic transport coefficients on temperature and the number of water molecules has been investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1233–1236, July, 1995.The present work was made possible in part by financial support of the International Science Foundation (Grant MPG000) and the Russian Foundation for Basic Research (Grant 93-03-4205).     

Nanoscopic Structure of a Metallo‐supramolecular Polyelectrolyte–Amphiphile Complex,Elucidated by X‐ray Scattering and Molecular Modeling

A combination of molecular modeling and X‐ray scattering was used to elucidate the structure of the metallosupramolecular polyelectrolyte–amphiphile complex (PAC) self‐assembled from Fe^II, 1,4‐bis(2,2′:6′,2″‐terpyridin‐4′‐yl)benzene, and dihexadecyl phosphate (DHP). An approximate structure of the semi‐ordered material was derived from the analysis of the X‐ray scattering data. The experimental data provided sufficient input for obtaining a useful starting configuration for molecular modeling. Various models of the supramolecular architecture are presented and discussed in terms of their total energies and scattering patterns. In an iterative approach each level of the structural hierarchy was refined until satisfactory agreement of calculated and experimental scattering patterns was reached. The remarkable sensitivity of the simulated scattering curves to even the smallest structural changes at all length scales restricts the arbitrariness of modeling. The final model of PAC consists of flat lamellae of alternating strata of interdigitated DHP monolayers and nematically ordered polyelectrolyte chains.