Gas transport in metal organic framework-polyetherimide mixed matrix membranes: The role of the polyetherimide backbone structure

We report on how the morphology of the polymer matrix, i.e. amorphous vs. semi-crystalline, affects the gas transport properties in a series of mixed matrix membranes (MMMs) using Cu3(BTC)2 as the metal organic framework (MOF) filler. The aim of our work is to demonstrate how incorporation of Cu3(BTC)2 affects the polyetherimide matrix morphology and thereby highlighting the importance of selecting the appropriate polyetherimide matrix for mixed matrix membranes. We used three amorphous poly(etherimide)s with very similar backbone structures. Polyetherimide ODPA-P1 was used as a linear flexible matrix, aBPDA-P1 is a non-linear rigid matrix and 6FDA-P1 was selected because the backbone structure is similar to ODPA-P1 but replacing the oxygen linker with two bulky –CF3 groups results in a linear polymer with a low chain packing efficiency. Using an in-situ polymerization technique, up to 20 wt.% Cu3(BTC)2 could be homogenously dispersed in all three PEIs. The ODPA-P1 matrix crystallized when Cu3(BTC)2 was introduced as a filler. Gas permeation studies were performed by analyzing membrane performance using a 50:50 CO2:CH4 mixed gas feed. The presence of crystalline domains in ODPA-P1 resulted in a decrease in permeability for both CO2 and CH4 but the selectivity increased from 41 to 52 at 20 wt.% Cu3(BTC)2. The non-linear, rigid, aBPDA-P1 matrix remains amorphous when Cu3(BTC)2 is introduced. SEM images of the MMM cross-section revealed a sieve-in-a-cage morphology and at 20 wt.% Cu3(BTC)2, the permeation of both CO2 and CH4 increased by 68% thereby negating any change in selectivity. For 6FDA-P1 with 20 wt.% Cu3(BTC)2, only the permeability of CO2 increased by 68% resulting in an increase in selectivity of 33

Gas transport in metal organic framework-polyetherimide mixed matrix membranes: The role of the polyetherimide backbone structure

We report on how the morphology of the polymer matrix, i.e. amorphous vs. semi-crystalline, affects the gas transport properties in a series of mixed matrix membranes (MMMs) using Cu3(BTC)2 as the metal organic framework (MOF) filler. The aim of our work is to demonstrate how incorporation of Cu3(BTC)2 affects the polyetherimide matrix morphology and thereby highlighting the importance of selecting the appropriate polyetherimide matrix for mixed matrix membranes.\u3cbr/\u3eWe used three amorphous poly(etherimide)s with very similar backbone structures. Polyetherimide ODPA-P1 was used as a linear flexible matrix, aBPDA-P1 is a non-linear rigid matrix and 6FDA-P1 was selected because the backbone structure is similar to ODPA-P1 but replacing the oxygen linker with two bulky –CF3 groups results in a linear polymer with a low chain packing efficiency. Using an in-situ polymerization technique, up to 20 wt.% Cu3(BTC)2 could be homogenously dispersed in all three PEIs. The ODPA-P1 matrix crystallized when Cu3(BTC)2 was introduced as a filler. Gas permeation studies were performed by analyzing membrane performance using a 50:50 CO2:CH4 mixed gas feed. The presence of crystalline domains in ODPA-P1 resulted in a decrease in permeability for both CO2 and CH4 but the selectivity increased from 41 to 52 at 20 wt.% Cu3(BTC)2. The non-linear, rigid, aBPDA-P1 matrix remains amorphous when Cu3(BTC)2 is introduced. SEM images of the MMM cross-section revealed a sieve-in-a-cage morphology and at 20 wt.% Cu3(BTC)2, the permeation of both CO2 and CH4 increased by 68% thereby negating any change in selectivity. For 6FDA-P1 with 20 wt.% Cu3(BTC)2, only the permeability of CO2 increased by 68% resulting in an increase in selectivity of 33

Tunable Anion Exchange Membrane Conductivity and Permselectivity via Non-Covalent, Hydrogen Bond Cross-Linking

Ion exchange membranes (IEMs) are a key component of electrochemical processes that purify water, generate clean energy, and treat waste. Most conventional polymer IEMs are covalently cross-linked, which results in a challenging tradeoff relationship between two desirable properties─high permselectivity and high conductivity─in which one property cannot be changed without negatively affecting the other. In an attempt to overcome this limitation, in this work we synthesized a series of anion exchange membranes containing non-covalent cross-links formed by a hydrogen bond donor (methacrylic acid) and a hydrogen bond acceptor (dimethylacrylamide). We show that these monomers act synergistically to improve both membrane permselectivity and conductivity relative to a control membrane without non-covalent cross-links. Furthermore, we show that the hydrogen bond donor and acceptor loading can be used to tune permselectivity and conductivity relatively independently of one another, escaping the tradeoff observed in conventional membranes

High-Strength Liquid Crystal Polymer-Graphene Oxide Nanocomposites from Water

We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the β-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Advanced Soft MatterNovel Aerospace Material

Strong graphene oxide nanocomposites from aqueous hybrid liquid crystals

Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide

On the tertiary structure of poly-carbenes; Self-assembly of sp\u3csup\u3e3\u3c/sup\u3e-carbon-based polymers into liquid-crystalline aggregates

\u3cp\u3eThe self-assembly of poly(ethylidene acetate) (st-PEA) into van der Waals-stabilized liquid-crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp \u3csup\u3e3\u3c/sup\u3e-carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st-PEA could perhaps be expected to lead directly to rigid-rod behavior, molecular modeling reveals that individual st-PEA chains are actually highly flexible and should not reveal rigid-rod induced LC behavior. Nonetheless, st-PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self-aggregation of st-PEA into higher-order aggregates. According to MM/MD modeling st-PEA single helices adopt a flexible helical structure with a preferred trans-gauche syn-syn-anti-anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self-assemble into triple-helical aggregates. Higher-order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st-PEA into higher-order structures, and suggest the formation of rod-like particles. The dimensions derived from these light-scattering experiments correspond with st-PEA triple-helix formation. Langmuir-Blodgett surface pressure-area isotherms also point to the formation of rod-like st-PEA aggregates with similar dimensions as st-PEA triple helixes. Upon increasing the st-PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st-PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface-solution interface with shapes and dimensions matching st-PEA triple helices, in good agreement with the structures proposed by molecular modeling. X-ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st-PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st-PEA. Formation of higher-order aggregates explains the observed LC behavior of st-PEA, emphasizing the importance of the tertiary structure of synthetic polymers on their material properties. Coming around again: The self-assembly of polycarbenes into van der Waals stabilized liquid-crystalline (LC) aggregates is described. The LC behavior of these materials is unexpected for flexible sp\u3csup\u3e3\u3c/sup\u3e-carbon backbone polymers. The experimental measurements, supported by molecular mechanics-based molecular dynamic studies, suggest that the LC behavior is due to self-aggregation of st-PEA into triple-helix aggregates (st-PEA=syndiotactic poly(ethylidene acetate).\u3c/p\u3

Methyl-Thiazoles: A Novel Mode of Inhibition with the Potential to Develop Novel Inhibitors Targeting InhA in Mycobacterium tuberculosis

InhA is a well validated Mycobacterium tuberculosis (Mtb) target as evidenced by the clinical success of isoniazid. Translating enzyme inhibition to bacterial cidality by targeting the fatty acid substrate site of InhA remains a daunting challenge. The recent disclosure of a methyl-thiazole series demonstrates that bacterial cidality can be achieved with potent enzyme inhibition and appropriate physicochemical properties. In this study, we report the molecular mode of action of a lead methyl-thiazole, along with analogues with improved CYP inhibition profile. We have identified a novel mechanism of InhA inhibition characterized by a hitherto unreported “Y158-out” inhibitor-bound conformation of the protein that accommodates a neutrally charged “warhead”. An additional novel hydrophilic interaction with protein residue M98 allows the incorporation of favorable physicochemical properties for cellular activity. Notably, the methyl-thiazole prefers the NADH-bound form of the enzyme with a <i>K</i>_d of ∼13.7 nM, as against the NAD⁺-bound form of the enzyme

4-Aminoquinolone Piperidine Amides: Noncovalent Inhibitors of DprE1 with Long Residence Time and Potent Antimycobacterial Activity

4-Aminoquinolone piperidine amides (AQs) were identified as a novel scaffold starting from a whole cell screen, with potent cidality on Mycobacterium tuberculosis (Mtb). Evaluation of the minimum inhibitory concentrations, followed by whole genome sequencing of mutants raised against AQs, identified decaprenylphosphoryl-beta-D-ribose 2'-epimerase (DprE1) as the primary target responsible for the antitubercular activity. Mass spectrometry and enzyme kinetic studies indicated that AQs are noncovalent, reversible inhibitors of DprE1 with slow on rates and long residence times of similar to 100 min on the enzyme. In general, AQs have excellent leadlike properties and good in vitro secondary pharmacology profile. Although the scaffold started off as a single active compound with moderate potency from the whole cell screen, structure-activity relationship optimization of the scaffold led to compounds with potent DprE1 inhibition (IC50 < 10 nM) along with potent cellular activity (MIC = 60 nM) against Mtb