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The invaluable health, economic and social impacts of vaccination are hard to exaggerate. The ability to stabilize vaccines is urgently required for their equitable distribution without the dependence on the 'cold-chain' logistics. Herein, for the first time we report biomimetic-mineralization of live-viral vaccines using metal-organic frameworks (MOFs) to enhance their storage stability from days to months. Applying ZIF-8 and aluminium fumarate (Alfum), the Newcastle Disease Virus (NDV) V4 strain and Influenza A WSN strain were encapsulated with remarkable retention of their viral titre. The ZIF-8@NDV, ZIF-8@WSN and Alfum@WSN composites were validated for live-virus recovery using a tissue culture infectious dose (TCID 50) assay. With the objective of long-term stabilization, we developed a novel, trehalose (T) and skim milk (SM) stabilized, freeze-dried MOF@Vaccine composite, ZIF-8@NDV+T/SM. The thermal stability of this composite was investigated and compared with the control NDV and non-encapsulated, freeze-dried NDV+T/SM composite at 4 °C, RT, and 37 °C over a period of 12 weeks. We demonstrate the fragility of the control NDV vaccine which lost all viability at RT and 37°C by 12 and 4 weeks, respectively. Comparing the freeze-dried counterparts, the MOF encapsulated ZIF-8@NDV+T/SM demonstrated significant enhancement in stability of the NDV+T/SM composite especially at RT and 37 °C upto 12 weeks. Vaccination is undoubtedly one of the most effective medical interventions, saving millions of lives each year. However, the requirement of 'cold-chain' logistics is a major impediment to widespread immunization. Live viral vaccines (LVVs) are widely used vaccine types with proven efficacy and low cost. Nonetheless, their complex composition increases their susceptability to thermal stress. Several LVV thermostabilization approaches have been investigated, including their complex engineering and the facile addition of stabilizers. Still, the lack of a universal approach urgently requires finding a stabilization technique especially when additives alone may not be sufficient. Herein, we demonstrate MOF biomimetic-mineralization technology to encapsulate LVVs developing an optimised composite which significantly preserves vaccines without refrigeration for extended periods of time. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract This report presents a systematic investigation of the influence of fixed charge group concentration on salt diffusion coefficients in ion exchange membranes. Cross-linked cation and anion exchange membranes (CEMs and AEMs) having different fixed charge group concentrations and similar water content were synthesized via a one-step free radical copolymerization reaction. Concentration gradient-driven ion transport through the membranes was probed by measuring salt permeability coefficients as a function of salt concentration in the upstream solution. For all membranes, salt permeability coefficients increased by approximately one order of magnitude as external solution salt concentration increased from 0.01 to 1 M, predominantly due to similar increases in salt partition coefficients. On average, salt permeability coefficients for both series of membranes decreased with increasing fixed charge group concentration to nearly the same extent. Apparent salt diffusion coefficients, which were extracted from salt permeability and salt partition coefficients via the solution-diffusion model, changed to a greater extent for the AEMs than those for the CEMs despite similar changes in membrane fixed charge group concentration. The relative changes in apparent salt diffusion coefficients between AEMs and CEMs were attributed to differences in free volume of the membranes. This hypothesis was supported by positron annihilation lifetime spectroscopy measurements, which demonstrated variation in ortho-positronium lifetime values (a measure of free volume element size) for these membranes that correlated with variations in apparent salt diffusion coefficients. Highlights • IEMs synthesized with different fixed charge group concentrations and similar water content. • Salt permeability coefficients decreased with increasing fixed charge group concentration. • Changes in salt diffusion coefficients correlated with free volume element changes. • Fixed charge group concentration does not significantly influence salt diffusion coefficients. [ABSTRACT FROM AUTHOR]

Abstract: A series of sulfonated styrenic pentablock copolymers was characterized using positron annihilation lifetime spectroscopy (PALS). Ortho-positronium (o-Ps) lifetime was measured as a function of the polymer's degree of sulfonation and the environment in which the polymer was equilibrated. Samples ranged from an un-sulfonated styrenic pentablock copolymer to one with an ion exchange capacity (IEC) of 2.0meq/g(dry polymer), and the samples were equilibrated in either air having 50% relative humidity, de-ionized (DI) water, or 2000mgL−1 aqueous NaCl solution environments. The o-Ps lifetime, and thus, the average free volume element size, decreased as the polymer's degree of sulfonation increased and as the amount of water sorbed into the polymer increased, similar to reported decreases in o-Ps lifetime accompanying increased water sorption in uncharged cross-linked poly(ethylene glycol) hydrogels. The o-Ps lifetimes of the DI water equilibrated acid counter-ion form polymers were quite similar to those of the salt solution equilibrated sodium counter-ion form polymers, suggesting that the PALS data are not particularly sensitive to the counter-ion form of these hydrated polymers. Previously reported water and salt permeability data in polymers were correlated with the PALS data. Correlating water and salt permeability with free volume data, estimated using o-Ps lifetime, was complicated by the micro-phase separated nature of the block copolymers. The water permeability of polymers whose hydrophilic micro-domains are believed to be well connected correlated with free volume data, based on o-Ps lifetime. Salt permeability, however, did not correlate with free volume data estimated from o-Ps lifetime, according to free volume theory. In general, contributions of the hydrophobic micro-domain free volume to the PALS measurement frustrate the correlation of water and salt transport properties with PALS parameters in a manner that is not observed in other sulfonated and uncharged polymers. [Copyright &y& Elsevier]

Abstract: MFI-type zeolites were characterized using powder X-ray diffraction (XRD), and positron annihilation lifetime spectroscopy (PALS) to uncover the hierarchical porous properties with Si/Al ratios varying from 30 to >1000 (high silica MFI). Structural dynamics were observed in response to exposure of the zeolites to seawater solutions, mimicking service conditions for use in membrane desalination or other ionic solution applications (e.g. sensors). PALS results indicated MFI channels between 0.27 and 0.36nm. All materials had microporous grain boundaries of 1.1nm. Mesopores were also detected at approximately 8nm in size for all materials. However the volume of microporous grain boundaries reduced with increasing alumina as explained by increasing presence of cations. Seawater exposure had a strong and complex effect on all materials. Initially widely variable crystal dimensions were stabilized by seawater exposure. The highest alumina content ZSM-5 (Si/Al=30) demonstrated net exchange, replacing K+ from synthesis impurities with Na+ leading to little overall change in porous features. Higher silica materials, including high silica MFI, demonstrated an overall release of ions, principally Na+ and K+, which were liberated mainly from the zeolite channels, yet these materials adsorbed Ca2+ in the microporous grain boundaries and Mg2+ in the mesoporous grain boundaries. Si/Al=100 appeared to be a unique ratio, allowing the material to possess the same Na+ adsorption features (and hydrophilicity) of high alumina materials, but ion interactions resembling high silica materials. MFI-type zeolite is therefore shown to be highly configurable using Si/Al ratio for a wide variety of applications in the presence of ions. [Copyright &y& Elsevier]

Abstract: Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane''s salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a commercial Dow Filmtec SW30 membrane and 188×1019 per gram for an aromatic polyamide material prepared in house. The activation energy for diffusion of water through the active layer of SW30 was also evaluated and found to be 6.95kcal/mol, lower than the heat of liquefaction of water. This suggests that water does not permeate as individual molecules in the vapour state, but rather as clusters of water molecules. The free volume cavity size in the active layer as a function of moisture uptake was also investigated and the results were explained using a pore filling and pore swelling mechanism. This study sheds light on the mechanisms of water entry into the active layer, water transport through the active layer, and the corresponding response of the polymer chains, thereby giving critical insight for the development of more novel systems. [Copyright &y& Elsevier]

This work presents the impact of propane and n -butane on the CO 2 /CH 4 separation performance of both cellulose diacetate (CDA) and cellulose triacetate (CTA) membranes by exposing both pristine membranes to either propane (400 kPa) or n -butane (200 kPa) at room temperature (22 ± 2 °C) for 4 weeks. The propane and n -butane sorption isotherms in both membranes were anomalous at 35 °C. X-ray diffraction (XRD) results indicated that the crystalline nature of both polymers was altered by this exposure, although dynamic scanning calorimetry (DSC) did not detect a significant change in the overall crystallinity. Positron Annihilation Lifetime Spectroscopy (PALS) revealed that the average pore size of the CTA polymer and the number of free volume elements of both membranes also increased, even though the sorption uptake was less than 2 wt%. CO 2 and CH 4 permeabilities at 35 °C were essentially unaffected by the propane or n -butane exposure, indicating that while the crystalline regions of the polymer were affected, plasticization of the glassy amorphous region did not occur. There was a slight decrease in CH 4 permeability for the CDA membrane after n -butane exposure, consistent with a slight decline in the CH 4 solubility at this feed pressure. The propane and n -butane permeabilities were 0.029 Barrer at 300 kPa and 0.019 Barrer at 125 kPa for the fresh CTA membrane, but these fell significantly after long term exposure to these gases, possibly due to penetrant clustering. [Display omitted] •Exposure of cellulose acetate to propane or butane changes the crystallinity of the polymer. • Fractional free volume increases and pore size distribution changes, but no plasticization. • Small changes in CO 2 and CH 4 solubility observed after exposure. • No changes in permeability of CO 2 , CH 4 or He after exposure. • Propane and butane permeability falls after exposure. [ABSTRACT FROM AUTHOR]

The fundamental gas transport properties and physical aging behavior of a series of triptycene-based polyimides with various substitution groups were investigated. Wide-angle x-ray diffraction revealed that the 6FDA-1,4-triptycene polyimides exhibit two chain packing domains with d -spacing values of ~6.7 Å and ~5.3 Å, corresponding to triptycene-induced chain packing disruption and chain segments lacking the triptycene moiety, respectively. Positron annihilation lifetime spectroscopy (PALS) showed a bimodal distribution of microcavity size made up of triptycene cleft cavities that are ~3 Å diameter and larger interchain cavities with an average diameter of ~7 Å. Additionally, PALS confirmed 6FDA-1,4-trip_CH 3 has the lowest fractional free volume, primarily due to smaller contributions from the interchain cavities, and 6FDA-1,4-trip_CF 3 has the largest fractional free volume. It was also found that the addition of substituent groups had a unique and positive effect on the aging properties over nine months, in which the addition of CH 3 and CF 3 groups led to permeability increases of ~20% and ~40%, respectively. This is caused by the combination of the lowered driving force for physical aging, the substituent groups sterically hindering tighter packing with time, and the interconnectivity and/or unblocking of free volume over time through small-scale, local chain motion. [ABSTRACT FROM AUTHOR]

In light of increasing concerns about climate change, there is a growing need for innovative solutions to address CO 2 emissions. Addressing this urgency, this work presents a unique approach to CO 2 separation utilizing composite membranes of organic ionic plastic crystals (OIPCs) with ether-functionalized cations and poly (vinylidene fluoride- co -hexafluoropropylene) (PVDF-HFP). Here we report the gas separation performance of OIPC-based membranes of 3,3-dimethyloxazolidinium [C 1 moxa]+, 4-ethyl-4-methylmorpholinium [C 2 mmor]+ and 4-isopropyl-4-methylmorpholinium [C i3 mmor]+ cations paired with the bis(fluorosulfonyl)imide [FSI]- anion. These composites demonstrated very good gas separation properties, especially [C 1 moxa][FSI] which produced a permeability of 63 barrer for CO 2 and an overall selectivity (CO 2 /N 2) of 205, which is the highest amongst all the OIPCs reported so far. Additionally, a large change in separation performance was observed for the [C i3 mmor][FSI] membrane upon heating above the solid-solid phase transition (II - I) at 48 °C; the CO 2 permeability increased from 7 to 163 barrer and an approximately 3-fold increase in selectivity was observed. These findings advance the design of composite membranes based on OIPCs towards increased selectivity and sustained effectiveness in the separation of light gases. [Display omitted] • CO 2 separation performance in organic ionic plastic crystals (OIPCs) based membranes was studied. • Ether-functionalized cation in OIPCs play a key role in high permeability/selectivity of CO 2. • High CO 2 permeability is attributed to OIPCs' phase transition and free volume as well as high solubility of CO 2 in these membranes. [ABSTRACT FROM AUTHOR]

Cellulose acetate is the predominant material used in membrane separation of acid gases from natural gas and biogas. However, the sensitivity of these membranes to water vapor is not well understood. In this work, flat-sheet membranes of two different degrees of acetylation, were exposed to both dry and humidified CH 4 and CO 2 /CH 4 mixtures. Positron Annihilation Lifetime Spectroscopy experiments showed that the number of free volume elements decreased as water concentration increased, indicating pore filling effects. The size of the free volume elements declined initially, followed by an increasing trend at vapor partial pressures greater than 2.5 kPa, indicating polymer swelling. Gas permeabilities of CH 4 and CO 2 followed a similar trend, with an initial decline due to hindered diffusion and competitive sorption, followed by an increase as the humidity exceeded 2.5 kPa. Water vapor permeabilities increased from 11,000 to 27,000 Barrer as the water activity increased but a change in the rate of increase was also noted at 2.5 kPa. At humidities in excess of 0.8, the extent of membrane swelling was such that equilibrium was not established even after 8 h of operation. Importantly, plasticization had significantly less impact on the polymer with a higher degree of acetylation. [ABSTRACT FROM AUTHOR]

Abstract: The presence of water vapor in a membrane gas separation system is known to cause plasticization and/or competitive sorption with other gas species. Using appropriate mathematical models to interpret such a multi-component system is of considerable practical importance. In an earlier publication, we reported the permeation properties of water vapor and its impact on the membrane performance for two polyimides; 2,2′-bis(3,4′-dicarboxyphenyl) hexafluoropropane dianhydrid-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TMPDA) and poly(3,3′-4, 4′-benzophenone tetracarboxylic-dianhydride diaminophenylindane) (Matrimid® 5218) under mixed gas/water vapor feed streams (CH4, CO2 and H2O). In this work, mathematical models based on proven sorption and transport models for glassy polymers were derived to successfully describe and characterize the permeation of water vapor and the associated changes of membrane performance in such a multi-component system. Water vapor induced-plasticization effects were not predicted by these models for either polyimide. Instead, as vapor activity increased, these models predicted a decrease in diffusion coefficient. This decline could be related to vapor-induced pore filling, which was further verified using positron annihilation lifetime spectroscopy (PALS) measurements. Pore filling by water molecules or possibly water clusters affected not only the self-diffusional pathway but also that for other penetrating gas molecules (CH4 and CO2). The increasing trend of water vapor permeability over the range of vapor activity for both polyimides was caused by the net effect of increasing vapor solubility and decreasing vapor diffusivity. [Copyright &y& Elsevier]

Hybrid membranes, featuring combinations of inorganic and organic materials at the nanometre or molecular level, have been widely reported as providing superior separation performance compared with the traditional polymeric membranes. However, for rational design of membranes, there remains a major doubt as to how each constituent functions in the separation process. Herein, carbon nanotube (CNT) incorporated poly (vinyl alcohol) (PVA) membranes were analysed using pervaporation (PV) process for aqueous mixture separation. The impacts of CNT on the functional properties, morphologies and microscale structures of the PVA/CNT hybrid membranes was investigated by ATR-FTIR, AFM, SEM and positron annihilation lifetime spectroscopy (PALS). Further, a comparison of the interactions between the membrane and solvents (water and ethanol) were identified by swelling test and XRD. The resultant PVA/CNT hybrid membranes were then subject to both desalination and dehydration of ethanol. The results showed that PVA exhibited preferential adsorption of water over ethanol. The addition of CNT enlarged the fractional free volume (FFV) and enhanced water diffusivity (up to 185%), which indicated a diffusion-dominated type of the PVA/CNT hybrid membranes with a synergistic effect of CNT on water transport. The transport of Na+ ions through the membrane was examined to be with larger activation energy than that of ethanol during the separation process. This work investigated the state of polymer as well as the effect of nanofillers in the separation of water vs. non-volatile or volatile component for the first time, which can provide in-depth understanding of the polymer-based hybrid membranes for practical applications. • Intrinsic difference between desalination and dehydration of ethanol was investigated for PVA-based membrane. • Nanofillers play an important role in tuning the physicochemical properties with a synergistic effect on water transport. • In-depth understanding of how the transport property of PVA/CNT hybrid membrane changed was provided. [ABSTRACT FROM AUTHOR]

Herein, a series of novel triptycene-containing thermally rearranged poly(benzoxazole- co -imide) membranes (TPI-PBOs) with enhanced mechanical properties and gas separation performance are reported. The effects of chemical structures and poly(benzoxazole- co -imide) composition on the fractional free volume, polymer chain packing, microcavity size and size distribution, mechanical properties, and gas transport properties have been comprehensively investigated. Due to the incorporation of triptycene-containing non-TR-able polyimide segments, the resulting poly(benzoxazole- co -imide) films exhibited good mechanical properties even after being treated at 450 °C. The incorporation of bulky and rigid triptycene units led to significantly improved fractional free volume and gas transport properties compared to previously reported poly(benzoxazole- co -imide)s. Several triptycene-containing poly(benzoxazole- co -imide) films displayed excellent gas separation performance for H 2 /CH 4 , H 2 /N 2 , and CO 2 /CH 4 gas pairs that exceeded the 2008 upper bounds. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive characterization and detailed analyses of microporous structure and fundamental gas transport properties for a series of new pentiptycene-containing polyimide gas separation membranes prepared from custom-synthesized pentiptycene-based diamines and 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) to identify the molecular origins for fast and selective gas transport. Both experimental characterizations of inter-chain spacing and microporosity and molecular modeling analysis of chain conformations and rigidity suggested that rigid H-shape pentiptycene units effectively disrupted chain packing, resulting in large fractional free volume and consequent high gas permeabilities in these membranes. Atomic-level detection of free volume architecture by positron annihilation lifetime spectroscopy (PALS) analysis revealed a bimodal microcavity size distribution with cavity sizes of d 4 ~7–8 Å and d 3 ~3–4 Å in this series of membranes. The microcavity size and size distribution were found to be sensitively affected by the substituent groups in the pentiptycene monomer structure based on the mechanism of “partial filling” of internal molecular cavities defined by the shape of pentiptycene units. Analysis of fundamental gas transport properties in terms of diffusivity ( D ) and solubility ( S ) coefficients demonstrated that size sieving mechanism (diffusivity contribution) dominates the gas transport in these polymers and bimodal microcavity size distribution with ultrafine microporosity is responsible for the excellent H 2 -related gas separation performance. Superior resistance against physical aging was observed for these high-free-volume polymers, which is ascribed to the stable, configuration-induced microcavity structure constructed by the rigid pentiptycene units. [ABSTRACT FROM AUTHOR]

Thermally rearranged (TR) polymers are formed through a thermally induced solid-state reaction of polyimides or polyamides that contain nucleophilic reactive groups ortho-positioned to their diamine. Naturally, the transport properties of TR polymers are intimately related to the chemical structure and reactivity of their precursors. Herein, we report characterization and transport properties for three poly(hydroxyimide) precursors prepared via thermal imidization in solution and for their corresponding TR polymers. Structural modifications to the polymer backbone can be used to control thermal rearrangement reaction kinetics. In regards to TR polymer formation, samples prepared from diamines with biphenyl functionality reacted more efficiently than those prepared from diamines with hexafluoroisopropylidene-linked aromatic units. However, hexafluoroisopropylidene functional units provided the highest combinations of permeability and selectivity for separations involving H 2 , N 2 , O 2 , CH 4 , and CO 2 . Differences in permeability between samples correlated well with changes in free volume, and 3 poly(hydroxyimide)s showed unusually high selectivities for their given free volume. The effect of synthesis route was also investigated for a specific TR polymer derived from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). Poly(hydroxyimide) precursors prepared via thermal imidization in solution and thermal imidization in the solid-state showed nearly identical permeabilities and selectivities regardless of synthesis route. However, after thermal rearrangement, the TR polymers prepared from polyimides synthesized via solid-state imidization have higher gas permeabilities than their solution-imidized analogs. In addition to light gas permeabilities, plasticization effects were investigated with CO 2 hysteresis loops for all samples, and pure-gas olefin/paraffin permeabilities were determined for a TR polymer derived from 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF) and 6FDA. With the exception of HAB–6FDA polyimides, pure-gas CO 2 feed pressures up to approximately 50 bar do not reveal a plasticization pressure point, but conditioning effects are observed for most samples. APAF–6FDA TR polymers have pure-gas permeabilities and selectivities beyond the propylene/propane upper bound. [ABSTRACT FROM AUTHOR]

Reacting ortho -functional poly(hydroxyimide)s via a high-temperature (i.e., 350 °C–450 °C) solid-state reaction produces polymers with exceptional gas separation properties for separations such as CO 2 /CH 4 , CO 2 /N 2 , and H 2 /CH 4 . However, these reactions render these so-called thermally rearranged (TR) polymers insoluble in common solvents, which prevent the use of certain experimental characterization techniques such as solution-state nuclear magnetic resonance (NMR) from identifying their chemical structure. In this work, we seek to identify the chemical structure of TR polymers by synthesizing a partially soluble TR polymer from an ortho -functional poly(hydroxyamide). The chemical structure of this TR polymer was characterized using 1-D and 2-D NMR. By use of cross-polarization magic-angle spinning 13 C NMR, the structure of the polyamide-based TR polymer was compared to that of a polyimide-based TR polymer with a nearly identical proposed structure. The NMR spectra suggest that oxazole functionality is formed for both of these TR polymers. Furthermore, gas permeation results are provided for the precursor polymers and their corresponding TR polymer. The differences in transport properties for these polymers result from differences in the isomeric nature of oxazole-aromatic linkages and morphological differences related to free volume and free volume distribution. [ABSTRACT FROM AUTHOR]

Polymer ultrafiltration membranes with high water flux have long been pursued to improve filtration efficiency and reduce costs of industrial separation processes such as water treatment and food processing. However, increasing water flux is usually accompanied by decreased rejection property in these membranes. In this paper, we show that by using a polymer functionalized with hydrophobically ionizable groups as additive, polymer ultrafiltration membranes with an increasing concentration of the additive from the active layer to the supporting layer are produced in the membrane casting process due to slow hydration of the additive. The hydrated additive becomes hydrophilic after the membrane formation. The resulting membranes exhibit dramatically enhanced water permeability while maintaining excellent separation property. We demonstrate that polyethersulfone/tris(2,4,6-trimethoxyphenyl)polysulfone-methylene quaternary phosphonium chloride (PES/TPQP-Cl) membrane exhibits a water permeability of up to 14.6 l m −2 h −1 kPa −1 , which is 35 times that of PES membrane. The membrane also shows excellent anti-biofouling property. The work provides a new methodology for designing high-performance membranes for improving separation efficiency and exploring other novel applications. [ABSTRACT FROM AUTHOR]

Ceramic membranes made from zeolites possess the nanoporous structure required for desalination of saline water including seawater. In this research, an α-Al2O3 supported MFI-type silicalite membrane was synthesised by the direct in-situ crystallisation method via a single hydrothermal treatment in an autoclave under autogenous pressure. Desalination performance of the prepared silicalite membrane was carried out with a seawater solution (0.3wt% TDS (total dissolved solids)) over a long period of around 180 days at a constant pressure of 700kPa at various temperatures. The prepared silicalite membrane achieved a high rejection (>93%) for all major seawater ions including Na+ (except for K+, 83%) at an applied pressure of 700kPa and room temperature (22°C), but showed a continuous decrease in ion rejection when increasing the temperature from 22°C and 90°C. Permeation flux of the zeolite membrane significantly increased with increasing in temperature. Upon closer observation of the major cations, size selective diffusion in the zeolite membrane was observed over the temperatures tested. Larger ions Ca2+ and Mg2+ were less responsive to temperature than smaller ions Na+ and K+. No changes in membrane structure were observed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) after 180 days seawater exposure. However, energy-dispersive X-ray spectroscopy (EDS) mapping on the surface of the membrane revealed a small quantity of tightly bound divalent cations present in the structure, which appear to have penetrated the zeolite, accelerated by temperature. They were suspected to have altered the permstructure, explaining why original high rejections at room temperature were not reversed after heat exposure. The work has shown that zeolite membranes can desalinate seawater, but other unusual effects such as ion selective diffusion as a function of temperature indicate a unique property for desalination membrane materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] PDMS gas permeable membranes are synthesized varying the crosslinking temperatures. [•] Different membranes are evaluated for permeability towards N2, CO2 and CH4. [•] The crosslinking temperature alters the polymeric structure of PDMS membranes. [•] A change in the polymeric structure varies the gas permeability of PDMS membranes. [•] Maximization of gas permeability was found at a crosslinking temperature of 75°C. [ABSTRACT FROM AUTHOR]

Abstract: Within a polymer thin film, free volume elements have a wide range of size and topology. This broad range of free volume element sizes determines the ability for a polymer to perform molecular separations. Herein, six permeable thermally rearranged (TR) polymers and their precursors were studied. Using atomistic models, cavity size (free volume) distributions determined by a combination of molecular dynamics and Monte Carlo methods were consistent with experimental observation that TR polymers are more permeable than their precursors. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy. The diffusion, solubility and permeation of gases in TR polymers and their precursors were also simulated at 308 K, with results that agree qualitatively with experimental data. [Copyright &y& Elsevier]

Tert-butoxycarbonyl (t-BOC) is a thermally labile moiety that can be used to protect hydroxyl groups on polymers. In this study, t-BOC was appended onto a polyimide consisting of 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB), after which the polymer was formed into self-standing films. Solid-state thermal treatments were performed to systematically remove t-BOC moieties to alter the physical packing structure and concomitant gas transport properties of the polymer. Despite performing deprotection reactions well below the glass transition temperature of 6FDA-HAB (~300 °C), this free volume manipulation (FVM) approach produced only subtle differences in polymer density, fractional free volume, average free volume element size, and gas transport properties relative to the unprotected polymer. While these findings suggest that thermally removing covalently bound functional groups from polymer films can be used to manipulate free volume and gas transport performance for glassy polymers, more robust polymer systems than linear polyimides are required to preserve the nascent free volume architecture generated from this approach. Image 1 • Polymer packing was studied via thermal treatments on functionalized 6FDA-HAB. • Thermal treatments below the polymer T g can lead to polymer chain mobility. • FFV and transport property changes show that extent of treatment affects packing. • PALS suggests that packing may change from mechanisms besides densification. [ABSTRACT FROM AUTHOR]

Molecular separations using synthetic membranes have been widely recognized as energy-efficient processes relative to conventional separation technologies. Rational design of the membrane structures for attainment of exceptionally permselective materials is highly beneficial in this respect. Herein, an ultrathin organic-inorganic hybrid nanofilm is formed on a hydrophobic polytetrafluoroethylene porous substrate through a facile and scalable solution casting process, thereby realizing an intrusion-free composite structure. Nanosizing Ti 3 C 2 T x MXene and sulfosuccinic acid are incorporated as nanofiller and crosslinker to manipulate the structural rigidity and free-volume property by polymer-nanofiller interaction and polymer chain crosslinking while simultaneously rendering outstanding membrane transport property, selectivity and stability. The synthesized nanofilm composite membrane with thickness down to ≈230 nm, comparable with the lateral dimension of small-sized MXene (≈142 nm), exhibits outstanding pervaporative separation of water from various aqueous-ion or -alcohol mixtures with high throughput that is around 5–70 times of other reported polymer-based membranes. Transport modelling of this hybrid nanofilm suggests that ultralow-resistance permeation behavior induced by MXene nanosheets dominates as the nanofilm thickness approaches the filler size. Image 1 • An intrusion-free hybrid nanofilm was formed on hydrophobic substrate. • The nanofilm thickness approaches the dimension of small-sized MXene nanosheets. • MXene can effectively reduce water transport resistance of the hybrid membrane. • In-depth understanding of the water transport was provided by transport modelling. [ABSTRACT FROM AUTHOR]