31 Search Results

Abstract Molecular ferroelectric materials consist of organic and inorganic ions held together by hydrogen bonds, electrostatic forces, and van der Waals interactions. However, ionically tailored multifunctionality in molecular ferroelectrics has been a missing component despite of their peculiar stimuli-responsive structure and building blocks. Here we report molecular ionic ferroelectrics exhibiting the coexistence of room-temperature ionic conductivity (6.1 × 10 ⁻⁵  S/cm) and ferroelectricity, which triggers the ionic-coupled ferroelectric properties. Such ionic ferroelectrics with the absorbed water molecules further present the controlled tunability in polarization from 0.68 to 1.39 μC/cm ² , thermal conductivity by 13% and electrical resistivity by 86% due to themore » proton transfer in an ionic lattice under external stimuli. These findings enlighten the development of molecular ionic ferroelectrics towards multifunctionality.« less

Atomic layer deposition (ALD) creates uniform sub-nanometer films on a variety of surfaces and nanopore walls and has been used to modify polymers to improve surface affinity towards specific molecules, solvent resistance, and barrier properties to gases and vapors. Here, for the first time, we demonstrate that few-cycle ALD can be used to engineer functional polymers at a sub-nanometer scale to improve both molecular size-sieving ability and counterintuitively, gas permeability. Particularly, 1-cycle ALD treatment of polybenzimidazole (PBI) by sequential exposure to trimethylaluminum (TMA) and water vapor remarkably increases H₂ permeability by 120% - 270% and H₂/CO₂ selectivity by 30% atmore » 35–200 °C. The ALD not only deposits an AlOx layer on the surface but also enables the TMA to infiltrate and react with the bulk PBI to form an AlO_x network, disrupting polymer chain packing and increasing chain rigidity. The membrane exhibits excellent stability when challenged with simulated syngas, overcoming the permeability/selectivity tradeoff for H₂/CO₂ separation. In conclusion, this study showcases a facile and scalable way of engineering polymeric membranes at a sub-nanometer level to improve molecular separation performance.« less

Thin-film composite membranes are a leading technology for post-combustion carbon capture, and the key challenge is to fabricate defect-free selective nanofilms as thin as possible (100 nm or below) with superior CO₂/N₂ separation performance. Herein, we developed high-performance membranes based on an unusual choice of semi-crystalline blends of amorphous poly(ethylene oxide) (aPEO) and 18-crown-6 (C6) using two nanoengineering strategies. First, the crystallinity of the nanofilms decreases with decreasing thickness and completely disappears at 500 nm or below because of the thickness confinement. Second, polydimethylsiloxane is chosen as the gutter layer between the porous support and selective layer, and its surfacemore » is modified with bio-adhesive polydopamine (<10nm) with an affinity toward aPEO, enabling the formation of the thin, defect-free, amorphous aPEO/C6 layer. For example, a 110 nm film containing 40 mass % C6 in aPEO exhibits CO₂ permeability of 900 Barrer (much higher than a thick film with 420 Barrer), rendering a membrane with a CO₂ permeance of 2200 GPU and CO₂/N₂ selectivity of 27 at 35 °C, surpassing Robeson’s upper bound. Finally, this work shows that engineering at the nanoscale plays an important role in designing high performance membranes for practical separations.« less

Abstract Nanoparticles (NPs) at high loadings are often used in mixed matrix membranes (MMMs) to improve gas separation properties, but they can lead to defects and poor processability that impede membrane fabrication. Herein, it is demonstrated that branched nanorods (NRs) with controlled aspect ratios can significantly reduce the required loading to achieve superior gas separation properties while maintaining excellent processability, as demonstrated by the dispersion of palladium (Pd) NRs in polybenzimidazole for H ₂ /CO ₂ separation. Increasing the aspect ratio from 1 for NPs to 40 for NRs decreases the percolation threshold volume fraction by a factor of 30,more » from 0.35 to 0.011. An MMM with percolated networks formed by Pd NRs at a volume fraction of 0.039 exhibits H ₂ permeability of 110 Barrer and H ₂ /CO ₂ selectivity of 31 when challenged with simulated syngas at 200 °C, surpassing Robeson's upper bound. This work highlights the advantage of NRs over NPs and nanowires and shows that right‐sizing nanofillers in MMMs is critical to construct highly sieving pathways at minimal loadings. This work paves the way for this general feature to be applied across materials systems for a variety of chemical separations.« less

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Abstract Mixed matrix materials (MMMs) hold great potential for membrane gas separations by merging nanofillers with unique nanostructures and polymers with excellent processability. In situ growth of the nanofillers is adapted to mitigate interfacial incompatibility to avoid the selectivity loss. Surprisingly, functional polymers have not been exploited to co‐grow the nanofillers for membrane applications. Herein, in situ synergistic growth of crystalline zeolite imidazole framework‐8 (ZIF‐8) in polybenzimidazole (PBI), creating highly porous structures with high gas permeability, is demonstrated. More importantly, PBI contains benzimidazole groups (similar to the precursor for ZIF‐8, i.e., 2‐methylimidazole) and induces the formation of amorphous ZIFs, enhancingmore » interfacial compatibility and creating highly size‐discriminating bottlenecks. For instance, the formation of 15 mass% ZIF‐8 in PBI improves H ₂ permeability and H ₂ /CO ₂ selectivity by ≈100% at 35 °C, breaking the permeability/selectivity tradeoff. This work unveils a new platform of MMMs comprising functional polymer‐incorporated amorphous ZIFs with hierarchical nanostructures for various applications.« less

Polybenzimidazole is doped with aromatic polycarboxylic acids to form supramolecular assemblies achieving strong size-sieving ability and thus high H2/CO2 selectivity.

Mixed matrix materials (MMMs) containing nanofillers dispersed in continuous polymer matrices have emerged as an exciting and versatile platform to develop membranes with superior CO₂/N₂ separation performance for post-combustion carbon capture. Both polymers and nanofillers can be vertically designed and engineered to combine the advantages of excellent processability (derived from polymers) and strong size-sieving ability or/and significant permanent porosity (originated from nanofillers). However, the MMMs face major challenges, such as interfacial incompatibility, particle agglomeration, and poor thin-film formability. This report provides a comprehensive yet critical review of various polymers and nanofillers (such as metal-organic frameworks, covalent organic frameworks, and two-dimensionalmore » materials) with promising CO₂/N₂ separation properties. We exhaustively describe strategies to improve interfacial compatibility, such as in situ syntheses of polymers and nanofillers and functionalization of both components to improve adhesion. Moreover, we highlight various approaches to engineer the MMMs into thin-film composite (TFC) membranes. The review reveals the structure/property relationship in these MMMs and outlines the challenges and opportunities to realize their potential for practical applications.« less

With its high content of CO₂-philic ether oxygen groups, poly(1,3-dioxolane) (PDXLA) has emerged as an attractive platform to achieve excellent CO₂/N₂ separation properties for post-combustion carbon capture. Herein we demonstrate that the separation properties of PDXLA can be further enhanced by plasticizing with miscible polyethylene glycol (PEG)-based additives using an integrated experimentation and modeling approach. The effects of the chain end groups and loading level of the additives on the physical properties of the blends are thoroughly investigated, including glass transition temperature (T_g), fractional free volume, and gas transport properties, and the effects can be satisfactorily described using models availablemore » for homogeneous blends. Notably, a T_g-integrated free volume model is adapted to successfully interpret the unified effect of the blend composition and temperature on gas diffusivity and permeability. A sample containing 45 mass% PEG dimethyl ether (PEGDME with a molecular mass of 240 g/mol) displays stable mixed-gas CO₂ permeability of 1540 Barrer and CO₂/N₂ selectivity of 40 when challenged with a model flue gas at 60 °C, outperforming Robeson's 2008 upper bound. Elucidating how small plasticizers impact gas transport in homogeneous blends may unravel a facile way to design high-performance membranes for gas separations.« less