8 research outputs found

    High Performance Nanofiltration Membrane for Effective Removal of Perfluoroalkyl Substances at High Water Recovery

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    We demonstrate the fabrication of a loose, negatively charged nanofiltration (NF) membrane with tailored selectivity for the removal of perfluoroalkyl substances with reduced scaling potential. A selective polyamide layer was fabricated on top of a poly­(ether sulfone) support via interfacial polymerization of trimesoyl chloride and a mixture of piperazine and bipiperidine. Incorporating high molecular weight bipiperidine during the interfacial polymerization enables the formation of a loose, nanoporous selective layer structure. The fabricated NF membrane possessed a negative surface charge and had a pore diameter of ∼1.2 nm, much larger than a widely used commercial NF membrane (i.e., NF270 with pore diameter of ∼0.8 nm). We evaluated the performance of the fabricated NF membrane for the rejection of different salts (i.e., NaCl, CaCl<sub>2</sub>, and Na<sub>2</sub>SO<sub>4</sub>) and perfluorooctanoic acid (PFOA). The fabricated NF membrane exhibited a high retention of PFOA (∼90%) while allowing high passage of scale-forming cations (i.e., calcium). We further performed gypsum scaling experiments to demonstrate lower scaling potential of the fabricated loose porous NF membrane compared to NF membranes having a dense selective layer under solution conditions simulating high water recovery. Our results demonstrate that properly designed NF membranes are a critical component of a high recovery NF system, which provide an efficient and sustainable solution for remediation of groundwater contaminated with perfluoroalkyl substances

    Elements Provide a Clue: Nanoscale Characterization of Thin-Film Composite Polyamide Membranes

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    In this study, we exploit the nitrogen–sulfur elemental contrast of thin-film composite (TFC) polyamide membranes and present, for the first time, the application of two elemental analysis techniques, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM–EDX) and X-ray photoelectron spectroscopy (XPS) C<sub>60</sub><sup>+</sup> ion-beam sputtering, to elucidate the nanoscale structure and chemical composition of the polyamide–polysulfone interface. Although STEM–EDX elemental mapping depicts the presence of a dense polyamide layer at the interface, it is incapable of resolving the elemental contrast at nanoscale resolution at the interfacial zone. Depth-resolved XPS C<sub>60</sub><sup>+</sup> ion-beam sputtering enabled nanoscale characterization of the polyamide–polysulfone interface and revealed the presence of a heterogeneous layer that contains both polyamide and polysulfone signatures. Our results have important implications for future studies to elucidate the structure–property–performance relationship of TFC membranes

    Rational Design of a Block Copolymer with a High Interaction Parameter

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    A series of poly­(4-<i>tert</i>-butylstyrene-<i>block</i>-2-vinylpyridine) [P­(tBuSt-<i>b</i>-2VP)] block copolymers (BCPs) with varying volume fractions, molecular weights, and narrow dispersities were synthesized from the commercially available monomers by sequential living anionic polymerization. The copolymers were thoroughly characterized by <sup>1</sup>H NMR spectroscopy, size exclusion chromatography, thermal gravimetric analysis, and differential scanning calorimetry (DSC). To examine the effect of the <i>tert</i>-butyl group on the effective interaction parameter (χ<sub>eff</sub>) relative to poly­(styrene-<i>block</i>-2-vinylpyridine) [(P­(S-<i>b</i>-2VP)], the self-assembly of symmetric copolymers was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy. Order-to-disorder transitions (ODTs) were identified by both DSC and SAXS on five copolymers, to define the equation χ<sub>eff</sub>(<i>T</i>) = (67.9 ± 1.3)/<i>T</i> – (0.0502 ± 0.0029), which shows a higher enthalpic contribution to χ<sub>eff</sub> than P­(S-<i>b</i>-2VP) and approximately 1.5 times larger χ<sub>eff</sub>. This enables a minimum full pitch of 9.6 nm for the symmetric copolymers. Asymmetric copolymers were also examined for bulk self-assembly by SAXS and TEM, exploring both P2VP and PtBuSt cylindrical phases with diameters as small as 6 nm. Feasibility of thin film assembly by thermal annealing was demonstrated for a P2VP cylinder forming BCPs to yield parallel cylinders that were seeded with Pt ions and etched to yield Pt nanowires with diameters as small as 5.8 nm

    Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers

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    We demonstrate through isomeric effect the modulation of thermal properties of poly­(hydroxystyrene) (PHS)-based block copolymers (BCPs). A minimal structural change of substituting 3HS for 4HS in the BCP results in a drastic decrease in <i>T</i><sub>g</sub>, which in turn enables the thin film assembly of the BCP via thermal annealing. We synthesized a series of poly­(3-hydroxystyrene-<i>b</i>-<i>tert</i>-butylstyrene) [P­(3HS-<i>b</i>-<i>t</i>BuSt)] and poly­(4-hydroxystyrene-<i>b</i>-<i>tert</i>-butylstyrene) [P­(4HS-<i>b</i>-<i>t</i>BuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS monomer and <i>t</i>BuSt followed by deprotection. Measured <i>T</i><sub>g</sub> of P­(3HS) was ∼20–30 °C lower than P­(4HS) of comparable molecular weights. As a result, thermally driven self-assembly of P­(3HS-<i>b</i>-tBuSt) BCPs in both bulk and thin film is demonstrated. For P­(4HS-<i>b</i>-tBuSt) thermal annealing in thin-film at high temperatures results in poorly developed morphology due to cross-linking reaction of the 4HS block. The smallest periodicity observed for P­(3HS-<i>b</i>-tBuSt) was 8.8 nm in lamellar and 11.5 nm in cylindrical morphologies. The functionality of the 3HS block was exploited to incorporate vapor phase metal oxide precursors to generate sub-10 nm alumina nanowires

    Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

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    Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

    Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

    No full text
    Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

    Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

    No full text
    Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

    Molecular Design of Liquid Crystalline Brush-Like Block Copolymers for Magnetic Field Directed Self-Assembly: A Platform for Functional Materials

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    We report on the development of a liquid crystalline block copolymer with brush-type architecture as a platform for creating functional materials by magnetic-field-directed self-assembly. Ring-opening metathesis of <i>n</i>-alkyloxy cyanobiphenyl and polylactide (PLA) functionalized norbornene monomers provides efficient polymerization yielding low polydispersity block copolymers. The mesogenic species, spacer length, monomer functionality, brush-chain length, and overall molecular weight were chosen and optimized to produce hexagonally packed cylindrical PLA domains which self-assemble and align parallel to an applied magnetic field. The PLA domains can be selectively removed by hydrolytic degradation resulting in the production of nanoporous films. The polymers described here provide a versatile platform for scalable fabrication of aligned nanoporous materials and other functional materials based on such templates
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