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Silver ions dissolved in a polymer matrix are additionally coordinated by carbonyl oxygens of asparagines and their counter anions interact with cationic sites, resulting in the enhanced activity of the silver ion as an olefin carrier for facilitated olefin transport.

Abstract: Cast Nafion and sulfonated poly[styrene-b-(ethylene-r-butylene)-b-styrene] copolymer (sSEBS)-based composite membranes containing different amounts of organic nanorod-shaped polyrotaxane (PR) were prepared and characterized, with the aim of improving the methanol barrier property of polymer electrolyte membranes (PEMs) for application in direct methanol fuel cells (DMFCs). PR was prepared using the inclusion complex reaction between α-cyclodextrin (α-CD) and poly(ethylene glycol) (PEG) of different molecular weights. The addition of PR to the structure of sSEBS, which involves hexagonal packing of cylinders, reduces the proton conductivity, as well as the methanol permeability, implying the creation of a tortuous path for methanol. The addition of PR to Nafion with ionic clusters reduced the crystallinity. The conductivity of the Nafion composite membranes increased on PR addition and decreased at higher PR contents. The organic PR inside the membrane changed the morphology during membrane preparation and provided a tortuous path for the transport of methanol. All of the sSEBS- and Nafion-based PR composite membranes showed higher selectivity parameter. [Copyright &y& Elsevier]

Abstract: Liquid phase isoprene/n-pentane mixtures can be separated through the use of facilitated transport membranes containing complexes of silver ions with an ionic liquid (IL). 1-Butyl-3-methyl imidazolium tetrafluoroborate and zwitterion-type imidazolium compounds containing covalently-bound sulfonate groups form complexes with AgX (X=BF4, NO3, and ClO4). Facilitated isoprene transport has been observed with selectivities that depend on the counteranion of the silver salt. The facilitated transport phenomena of the olefin and IL/silver complexes were investigated theoretically by calculating their complexation energies (i.e., the energy of formation of the silver complexes with the olefin) with the density functional theory method. Among polymer/silver salt systems, the polymer/AgBF4 system has been found to be generally more favorable for facilitated olefin transport than the polymer/AgNO3 system because of the low lattice energy of AgBF4. However, there is a different trend for IL/AgX systems. This difference may arise because the positively charged components of the IL can interact with the anions of the silver salt, which changes the olefin complexation activity. For IL/AgX systems, the selectivity varies inversely with the complexation energy, which implies that the diffusion of the carrier may be the significant factor affecting isoprene/n-pentane separation, once the appropriate complexation has occurred between olefin molecules and the ILsilver complexes. [Copyright &y& Elsevier]

Remarkably high-performance membranes are developed by physically dispersing silver ionic aggregates in inert polymer such as poly(dimethyl siloxane) (PDMS). The mixed gas selectivity for propylene/propane reaches nearly 200, to our knowledge the highest value ever reported for the solid state, whereas other membranes reported up to now show ∼60 of propylene/propane selectivity. Physical dispersion of silver salt in the inert polymers without specific interaction is observed by FT-IR, FT-Raman and wide angle X-ray scattering (WAXS). It is also found that the crystalline silver ionic aggregates are completely dissolved under the propylene environment, representing that propylene is a good ligand for coordination to silver ions. The inert membranes are functional at any loading level and hence a threshold carrier concentration does not exist. [Copyright &y& Elsevier]

Recently, researches about polymer electrolytes have been spotlighted owing to their potential applications in polymer batteries, fuel cells and solar cells. To our knowledge, no report has been published on polymer electrolytes by π-complexation between transition metal ion and olefinic ligand of a polymer matrix although several have been reported by the coordination between metal ion and nonbonding electrons of oxygen, nitrogen, etc. In this communication, we report that polymer electrolytes consisting of silver salt and polymer containing C&z.dbnd6;C bond are developed and especially applied to the facilitated olefin transport membranes for the separation of olefin/paraffin mixtures. [Copyright &y& Elsevier]

Abstract: π-Complexes consisting of silver salts such as AgBF4 and AgCF3SO3 dissolved in poly(styrene-b-butadiene-b-styrene) (SBS) block copolymers have been prepared for use as facilitated olefin transport membranes. Facilitated olefin transport is not observable up to the silver mole fraction of 0.14, a threshold concentration, above which it increases almost linearly with the silver salt concentration. FT-IR spectra of these complexes show that silver ions selectively coordinate with the Cf PB blocks up to the silver mole fraction of 0.14, and that the coordinative interaction of the silver ion with aliphatic Cnger than that with aromatic Cstingly, the bicontinuous morphology of the neat SBS block copolymer prepared from THF solution persists in the SBS complex with the salt concentrations less than 0.14. At high silver salt concentrations, the PS domains are additionally coordinated by silver ions and thus the morphology transition occurs from bicontinuous to lamellar. The threshold silver concentration of 0.14 for the facilitated olefin transport is nearly coincident with the composition at which the silver ions start coordinating with the aromatic Cf the PS blocks, suggesting their important role in determining overall transport properties. Therefore, we have shown that the transport properties of the SBS complex membranes are significantly affected by the coordinative interaction of the block copolymers with the silver ions and their membrane morphology. [Copyright &y& Elsevier]

Abstract: The reduction of silver ions to silver nanoparticles is an essential issue in polymer/silver salt complex membranes for facilitated olefin transport, because it has a critical influence on the long-term stability of membrane performance. In this study, the role of anions for the formation of silver nanoparticles in polymer/silver salt complexes was investigated. This role was assessed for the complexes of poly(N-vinyl pyrrolidone) (PVP) with three silver salts including AgBF4, AgCF3SO3, and AgNO3. Especially, UV irradiation to the membranes was used to clearly investigate the reduction behavior of silver ions. Separation performance test, UV–vis spectroscopy and transmission electron microscopy (TEM) clearly show that the reduction rate of silver ions strongly depends on the counteranions of salt, and has the following order: AgBF4 >AgCF3SO3 >AgNO3. This behavior of the formation of silver nanoparticles in polymer/silver salt complex membranes is explained in terms of the interaction strength of silver ions with the carbonyl oxygens of polymer, and that of silver ions with counteranions. It is concluded that when the former interaction is strong and the latter one is weak, the reduction rate of silver ions to silver nanoparticles is fast, and vice versa. These interactions were characterized using FT-IR, FT-Raman spectroscopy, and theoretical ab initio calculation. [Copyright &y& Elsevier]

Abstract: Previously we have found that the facilitated olefin transport through polymer/silver complex membranes is sensitive to the type of the counteranion of salt; the separation performances including the permeance and selectivity of propylene/propane are in the order of AgBF4>AgCF3SO3AgNO3. Here the polymer/silver salt complex membranes consisting of two mixed salts dissolved in poly(2-ethyl-2-oxazoline) (POZ) were prepared and tested for the separation of propylene/propane mixtures. Upon mixing AgNO3 with AgBF4 or AgCF3SO3, the selectivity of propylene/propane unusually increased in certain composition ranges. The permeation behavior was interpreted in terms of both the activity of silver ion as olefin carrier and the structural change of polymer electrolyte membranes using FT-IR spectroscopy and wide angle X-ray scattering (WAXS). As a result, the anomalous enhancement of selectivity was attributable mainly to the structural compactness of membranes, resulting from the increased transient cross-links of polymer chains by coordination of small sized AgNO3. [Copyright &y& Elsevier]

Abstract: Highly efficient proton-exchange membranes (PEMs) have been made by using polymer blends of water soluble poly(vinyl alcohol) and poly(styrene sulfonic acid-co-maleic acid) (i.e. PVA/PSSA–MA). Upon successive thermal and chemical treatments of the membranes, the methanol permeability decreased more than one order of magnitude compared with Nafion 117 but the proton conductivity was as high as 0.1Scm-1 at room temperature. The degrees of swelling of the membranes were controlled by adding a suitable crosslinker (i.e. glutaraldehyde) and varying the mole ratios of maleic acid groups to sulfonic acid groups. The characteristic hydrophilic/hydrophobic separation length of the crosslinked membrane (equilibrated in water) was shown to be smaller than that of Nafion 117 as inferred from the results of small-angle X-ray scattering (SAXS) analysis. Moreover, we could not observe the typical ionomer peak in the PVA/PSSA–MA membrane equilibrated with methanol from the SAXS profile, demonstrating very poor methanol affinity of the membrane matrix. It is believed that this structural feature contributes to the reduction of methanol permeability through the membranes. [Copyright &y& Elsevier]

Facilitated olefin transport membranes consisting of AgBF4 dissolved in poly(2-ethyl-2-oxazoline) (POZ) were prepared for use in propylene/propane separation. It was found that facilitated propylene transport through these membranes depends on their thickness. As the membrane thickness increases, the propylene permeability increases whereas the propane permeability remains almost constant, resulting in an increase in the membranes’ selectivity of propylene over propane. The concentration fluctuation model for facilitated transport in the solid state predicts a dependence of facilitated transport on thickness. In this note, we compare the dependence of the propylene permeability of POZ/AgBF4 membranes on their thickness with that predicted by the concentration fluctuation model. [Copyright &y& Elsevier]

Silver polymer electrolyte membranes consisting of poly(vinyl pyrrolidone) (PVP) and AgBF4 have previously exhibited remarkable separation performance with respect to propylene/propane gas mixtures. In this work, the effect of temperature on facilitated propylene transport is reported. The propylene permeance through the PVP/AgBF4 membranes decreased with increasing temperature, predominantly due to a decrease of the propylene concentration coordinated to silver ions, that is propylene solubility, as demonstrated by FT-IR spectroscopy. The propane permeance and the actual selectivity of propylene over propane decreased monotonously with increasing temperature. Unexpectedly, the propylene permeance further drops sharply when the temperature is increased higher than 70 °C. This anomalous behavior of the propylene permeance at temperatures above 70 °C can be explained by the deactivation of silver ions as active olefin carriers, i.e. the reduction of silver ions to silver metals. It is concluded that the silver ions as active olefin carriers rapidly convert to silver metals at temperatures above 70 °C, therefore becoming much less active olefin carriers, which results in the low propylene permeance. [Copyright &y& Elsevier]

A macrovoid-free, porous membrane with a sponge-like structure was obtained by phase inversion of a polyimide (PI)/γ-butyrolactone (GBL)/water system, whereas a membrane with a finger-like structure was obtained from a PI/N-methyl-2-pyrrolidinone (NMP)/water system. In this study, the effect of the molecular weight of poly(vinyl pyrrolidone) (PVP) additive (Mw: 360k and 40k) in two systems on membrane morphology has been investigated by the differences in phase separation rates and miscibility gaps. On addition of PVP into the PI casting solutions, the two systems exhibited significantly different membrane morphologies; the former augmented macrovoid formation while the latter suppressed formation of finger-like structures. The membrane morphology and the phase separation rate significantly depend on the molecular weight of PVP in PI/NMP/water system whereas those do insignificantly in PI/GBL/water system. The cloud points representing the miscibility gap do not depend on the molecular weight of PVP in both systems very much. Therefore, it is suggested that the morphology change in the PI/NMP/water system is mostly due to the change in the phase separation rate caused by the change in the solution viscosity upon addition of PVP. However, in the PI/GBL/water system, the molecular weight effect of PVP is not as significant as in the PI/NMP/water system, and the morphology change seems to be primarily due to the change in the miscibility gap. [Copyright &y& Elsevier]

Polymer electrolyte membranes consisting of AgBF4 dissolved in poly(ethylene phthalate) (PEP) exhibit significantly better long-term stability of performance in the separation of propylene/propane mixtures than AgBF4 in poly(2-ethyl-2-oxazoline) (POZ) membranes. This improvement in stability is due to the suppression of the reduction of silver ions to silver metal nanoparticles by the formation of stable chelates between the phthalic groups of PEP and silver ions, which was confirmed by the observation of a large shift of the PEP C&z.dbnd6;O stretching band with the addition of AgBF4; the peak shift for PEP/AgBF4 is twice that for POZ/AgBF4. Transmission electron micrograph (TEM) results confirmed that the rate of silver metal nanoparticle formation in PEP/AgBF4 is significantly lower than that in POZ/AgBF4. We conclude that the strong coordination between phthalic groups in PEP and silver ions which results in the formation of stable chelates is of pivotal importance in preventing the reduction of silver ions to silver metal and consequently in improving the performance of the membrane in the separation of propylene/propane mixtures. [Copyright &y& Elsevier]

Silver salts dissolved in amide group containing polymer such as poly(2-ethyl-2-oxazoline) (POZ) are labile to reduce to silver metals under UV-Vis light or heat. Since the reduction of silver ions to silver nanoparticles can change the separation performance of facilitated olefin transport through polymer membranes containing silver salt, it is attempted to prohibit the reduction of silver ion. It is found that the trace of water present in silver–polymer complex membranes participates in the reduction reaction and H+ ions are generated in a reversible reaction of the reduction process. In this respect, tetrafluoroboric acid (HBF4) was introduced as a proton donator to suppress the reduction of silver ion. The effects of HBF4 on the photoreduction derived by UV irradiation were characterized by mixed gas transport of ethylene/ethane, UV-Vis spectroscopy, scanning electron microscopy (SEM). [Copyright &y& Elsevier]