RESUMEN
Isoporous integral asymmetric membranes derived from the self-assembly of block copolymers combined with the non-solvent-induced phase separation (SNIPS) have gained great attention. To extend their utility, good control over pore size and surface functionality in a facile manner is highly desirable. Here, an approach is proposed to achieve this by quaternization of the poly(4-vinylpyridine) moiety of a polystyrene-block-poly(4-vinylpyridine) SNIPS membrane using alkyl iodides via a scalable gas-solid heterogeneous reaction. By changing the size of the alkyl groups of the quaternization agent and the degree of quaternization, the effective pore size of the membrane is tailored in a wide range from the ultrafiltration to the nanofiltration regime. A quaternization of approximately half of the 4VP repeating units of the membranes with methyl iodide, ethyl iodide, or 1-propyl iodide leads to a retention of methylene blue from a 10 mg L-1 aqueous solution of 96%, 87%, and 83%, respectively.
Asunto(s)
Membranas Artificiales , Poliestirenos/química , Polivinilos/química , Piridinas/química , Microscopía Electrónica de Rastreo , Estructura Molecular , Porosidad , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de SuperficieRESUMEN
Using the example of an integral-asymmetric isoporous membrane prepared from polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA), physical and chemical ways of post-treatment are introduced with the aim to tailor the pore size. These post-treatments are i) thermal annealing and ii) urethane chemistry of ethyl isocyanate (EI) in the presence of perfluoro(methyl cyclohexane). Via these approaches, the pore size of PS-b-PHEMA membranes is successfully tailored in the range of 10-20 nm with narrow pore size distribution by controlling the duration of thermal annealing and chemical reaction, respectively. The excellent hydrophilicity of the PS-b-PHEMA membrane is not changed by thermal annealing. The chemical postmodification using EI is associated with a loss of hydrophilicity with increasing conversion.
Asunto(s)
Polihidroxietil Metacrilato/química , Poliestirenos/química , Tamaño de la Partícula , Porosidad , Propiedades de SuperficieRESUMEN
A double-layer hollow fiber is fabricated where an isoporous surface of polystyrene-block-poly(4-vinylpyridine) is fixed on a support layer by co-extrusion. Due to the sulfonation of the support layer material, delamination of the two layers is suppressed without increasing the number of subsequent processing steps for isoporous composite membrane formation. Electron microscope-energy-dispersive X-ray spectroscopy images unveil the existence of a high sulfur concentration in the interfacial region by which in-process H-bond formation between the layers is evidenced. For the very first time, our study reports a facile method to fabricate a sturdy isoporous double-layer hollow fiber.
Asunto(s)
Membranas Artificiales , Poliestirenos/química , Polivinilos/química , Piridinas/química , Azufre/química , Técnicas Electroquímicas , Enlace de Hidrógeno , Microscopía Electrónica de Rastreo , Porosidad , Espectrometría por Rayos XRESUMEN
The formation of integral asymmetric membranes from ABC triblock terpolymers by non-solvent-induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post-functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements.
Asunto(s)
Polietilenglicoles/síntesis química , Poliestirenos/síntesis química , Polivinilos/síntesis química , Piridinas/síntesis química , Interacciones Hidrofóbicas e Hidrofílicas , Membranas Artificiales , Transición de Fase , Polietilenglicoles/química , Poliestirenos/química , Polivinilos/química , Piridinas/químicaRESUMEN
Block copolymers (BCPs) are promising materials for water purification. They enable the fabrication of integral asymmetric isoporous membranes with high permeability and good selectivity. Commonly, the characterization of such hierarchical structures is performed by conventional electron microscopy (EM) means, namely scanning and transmission electron microscopy (SEM and TEM, respectively). However, due to the inherent lack of contrast between BCP domains, external contrast agents are required to achieve informative, high-resolution imaging. In addition, such EM techniques are typically limited to a certain cross-section or surface morphology only. In this paper, we harness the selective growth of AlOx in the pore-forming domains of BCPs to create an internal and stable contrast difference between the blocks. This in turn allowed us to perform advanced three-dimensional characterization of the membranes with focused ion beam (FIB)-SEM and TEM tomography, providing an understanding of the 3D structure and properties such as 3D geometry of the pores, 3D tortuosity, and 3D permeability. This 3D characterization also provides better correlations between the membrane structure and its performance. Such knowledge can allow better design and fine-tuning of BCP membranes and other membranes for their applications.
RESUMEN
The organization of inorganic nanostructures within self-assembled organic or biological templates is receiving the attention of scientists interested in developing functional hybrid materials. Previous efforts have concentrated on using such scaffolds to spatially arrange nanoscopic elements as a strategy for tailoring the electrical, magnetic or photonic properties of the material. Recent theoretical arguments have suggested that synergistic interactions between self-organizing particles and a self-assembling matrix material can lead to hierarchically ordered structures. Here we show that mixtures of diblock copolymers and either cadmium selenide- or ferritin-based nanoparticles exhibit cooperative, coupled self-assembly on the nanoscale. In thin films, the copolymers assemble into cylindrical domains, which dictate the spatial distribution of the nanoparticles; segregation of the particles to the interfaces mediates interfacial interactions and orients the copolymer domains normal to the surface, even when one of the blocks is strongly attracted to the substrate. Organization of both the polymeric and particulate entities is thus achieved without the use of external fields, opening a simple and general route for fabrication of nanostructured materials with hierarchical order.
RESUMEN
Accomplishing on-demand molecular separation with a high selectivity and good permeability is very desirable for pollutant removal and chemical and pharmaceutical processing. The major challenge for sub-10 nm filtration of particles and molecules is the fabrication of high-performance membranes with tunable pore size and designed functionality. Here, a versatile top-down approach is demonstrated to produce such a membrane using isoporous block copolymer membranes with well-defined pore sizes combined with growth of metal oxide using sequential infiltration synthesis and atomic layer deposition (SIS and ALD). The pore size of the membranes is tuned by controlled metal oxide growth within and onto the polymer channels, enabling up to twofold pore diameter reduction. Following the growth, the distinct functionalities are readily incorporated along the membrane nanochannels with either hydrophobic, cationic, or anionic groups via straightforward and scalable gas/liquid-solid interface reactions. The hydrophilicity/hydrophobicity of the membrane nanochannel is significantly changed by the introduction of hydrophilic metal oxide and hydrophobic fluorinated groups. The functionalized membranes exhibit a superior selectivity and permeability in separating 1-2 nm organic molecules and fractionating similar-sized proteins based on size, charge, and hydrophobicity. This demonstrates the great potential of organic-inorganic-organic isoporous membranes for high-performance molecular separation in numerous applications.
RESUMEN
Membrane-based separation of organic molecules with 1-2 nm lateral dimensions is a demanding but rather underdeveloped technology. The major challenge is to fabricate membranes having distinct nanochannels with desired functionality. Here, a bottom-up strategy to produce such a membrane using a tailor-made triblock terpolymer featuring miscible end blocks with two different functional groups is demonstrated. A scalable multifunctional integral asymmetric isoporous membrane is fabricated by the solvent evaporation-induced self-assembly of the block copolymer combined with nonsolvent-induced phase separation. The membrane nanopores are readily functionalized using positively and negatively charged moieties by two straightforward gas-solid reactions. The pores of the post-functionalized membranes act as target-specific functional soft nanochannels due to swelling of the polyelectrolyte blocks in a hydrated state. The membranes show unprecedented separation selectivity of small molecules based on size and/or charge which demonstrates the potential of the proposed strategy to prepare next-generation nanofiltration membranes.
RESUMEN
Isoporous membranes can be prepared by a combination of self-assembly of amphiphilic block copolymers and the non-solvent induced phase separation process. As the general doctor-blade technique suffers from high consumption of expensive block copolymer, other methods to reduce its concentration in the casting solution are sought after. Decreasing the block copolymer concentration during membrane casting and applying the block copolymer solution on a support membrane to obtain ultrathin isoporous membrane layers with e.g., spraying techniques, can be an answer. In this work we focused on the question if upscaling of thin block copolymer membranes produced by spraying techniques is feasible. To upscale the spray coating process, three different approaches were pursued, namely air-brush, 1-fluid nozzles and 2-fluid nozzles as generally used in the coating industry. The different spraying systems were implemented successfully in a membrane casting machine. Thinking about future development of isoporous block copolymer membranes in application it was significant that a continuous preparation process can be realised combining spraying of thin layers and immersion of the thin block copolymer layers in water to ensure phase-separation. The system was tested using a solution of polystyrene-block-poly(4-vinylpyridine) diblock copolymer. A detailed examination of the spray pattern and its homogeneity was carried out. The limitations of this method are discussed.
RESUMEN
In this work, the possibility of creating a polymer-based adaptive scaffold for improving the hydrogen storage properties of the system 2LiH+MgB2+7.5(3TiCl3·AlCl3) was studied. Because of its chemical stability toward the hydrogen storage material, poly(4-methyl-1-pentene) or in-short TPXTM was chosen as the candidate for the scaffolding structure. The composite system was obtained after ball milling of 2LiH+MgB2+7.5(3TiCl3·AlCl3) and a solution of TPXTM in cyclohexane. The investigations carried out over the span of ten hydrogenation/de-hydrogenation cycles indicate that the material containing TPXTM possesses a higher degree of hydrogen storage stability.
RESUMEN
In this work, we present a novel synthetic route to diblock copolymers based on styrene and 3-vinylpyridine monomers. Surfactant-free water-based reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of styrene in the presence of the macroRAFT agent poly(3-vinylpyridine) (P3VP) is used to synthesize diblock copolymers with molecular weights of around 60 kDa. The proposed mechanism for the poly(3-vinylpyridine)-block-poly(styrene) (P3VP-b-PS) synthesis is the polymerization-induced self-assembly (PISA) which involves the in situ formation of well-defined micellar nanoscale objects consisting of a PS core and a stabilizing P3VP macroRAFT agent corona. The presented approach shows a well-controlled RAFT polymerization, allowing for the synthesis of diblock copolymers with high monomer conversion. The obtained diblock copolymers display microphase-separated structures according to their composition.
RESUMEN
In this paper, the formation of nanostructured triblock terpolymer polystyrene-b-poly(4-vinylpyridine)-b-poly(solketal methacrylate) (PS-b-P4VP-b-PSMA), polystyrene-b-poly(4-vinylpyridine)-b-poly(glyceryl methacrylate) (PS-b-P4VP-b-PGMA) membranes via block copolymer self-assembly followed by non-solvent-induced phase separation (SNIPS) is demonstrated. An increase in the hydrophilicity was observed after treatment of non-charged isoporous membranes from PS-b-P4VP-b-PSMA, through acidic hydrolysis of the hydrophobic poly(solketal methacrylate) PSMA block into a hydrophilic poly(glyceryl methacrylate) PGMA block, which contains two neighbored hydroxyl (-OH) groups per repeating unit. For the first time, PS-b-P4VP-b-PSMA triblock terpolymers with varying compositions were successfully synthesized by sequential living anionic polymerization. Composite membranes of PS-b-P4VP-b-PSMA and PS-b-P4VP-b-PGMA triblock terpolymers with ordered hexagonally packed cylindrical pores were developed. The morphology of the membranes was studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM). PS-b-P4VP-b-PSMA triblock terpolymer membranes were further treated with acid (1 M HCl) to get polystyrene-b-poly(4-vinylpyridine)-b-poly(glyceryl methacrylate) (PS-b-P4VP-b-PGMA). Notably, the pristine porous membrane structure could be maintained even after acidic hydrolysis. It was found that membranes containing hydroxyl groups (PS-b-P4VP-b-PGMA) show a stable and higher water permeance than membranes without hydroxyl groups (PS-b-P4VP-b-PSMA), what is due to the increase in hydrophilicity. The membrane properties were analyzed further by contact angle, protein retention, and adsorption measurements.
RESUMEN
We investigated the self-assembly of block copolymers during hollow fiber membrane (HFM) fabrication by conducting in situ small angle X-ray scattering (SAXS) and ex situ scanning electron microscopy (SEM) studies. SAXS enables us to follow the structural rearrangements after extrusion at different distances from the spinning nozzle. The kinetics of the spinning process is examined as a function of the composition of block copolymer solutions and the spinning parameters. We studied the influence of the extrusion rate on the block copolymer microdomains and their self-assembly in weakly segregated and ordered solutions. The addition of magnesium acetate (MgAc2) leads to the ordering of micelles in the block copolymer solution already at lower polymer concentrations and shows an increased number of micelles with larger domain spacing as compared to the pristine solution. The SAXS data show the effect of shear within the spinneret on the self-assembly of block copolymers and the kinetics of phase separation after extrusion. It is observed that the ordering of micelles in solutions is decreased as indicated by the loss of crystallinity while high extrusion rates orient the structures perpendicular to the fiber direction. The structural features obtained from in situ SAXS experiments are correlated to the structure in the block copolymer solutions in the absence of shear and the morphologies in flat sheet and HF membranes obtained by ex situ SEM. This allows a systematic and comparative study of the effects varying the microdomain ordering within different block copolymer solutions and the formed membrane structures.
RESUMEN
The purpose of this work is the structural analysis of graphene oxide (GO) and by means of a new structural model to answer the questions arising from the Lerf-Klinowski and the Lee structural models. Surface functional groups of GO layers and the oxidative debris (OD) stacked on them were investigated after OD was extracted. Analysis was performed successfully using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), X-ray photoemission spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, solid-state nuclear magnetic resonance spectroscopy (SSNMR), standardized Boehm potentiometric titration analysis, elemental analysis, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The analysis showed that graphene oxide layers, as well as oxidative debris contain different functional groups such as phenolic -OH, ketone, lactone, carboxyl, quinone and epoxy. Based on these results, a new structural model for GO layers is proposed, which covers all spectroscopic data and explains the presence of the other oxygen functionalities besides carboxyl, phenolic -OH and epoxy groups.
RESUMEN
In this work we present a method to manufacture flat sheet membranes with a thin isoporous block copolymer (BCP) layer (thickness <3 µm) by profile roller coating (breadth: 30 cm) on top of a porous support membrane. Highly diluted BCP-solutions were used for this coating process. While we cast membranes with dimensions of 30 cm × 50 cm in this work, the procedure can easily be extended to endless dimensions in this roll to roll (R2R) process. The method offers the possibility to save >95% of BCP raw material compared to common doctor blade casting, by strongly decreasing the layer thickness to below 3 µm in combination with a highly open substructure. Additionally, we report a straightforward method to investigate the influence of the solvent evaporation time between coating and precipitation (phase inversion) on the membrane morphology using one sample only, which also ensures that all other influencing parameters remain constant.
RESUMEN
Hollow fiber membranes (HFM) are fabricated from blend solutions of a polyethersulfone (PESU) with a sulfonated PESU (sPESU) or a sulfonated polyphenylenesulfone (sPPSU). The influence of different additives in the dope solution and different bore fluids on the HFM are studied. The addition of poly(sodium 4-styrene sulfonate) (PSSNa)/ethylene glycol (EG) to the dope solution results in an increased water flux of the HFM compared to its counterparts without this additive system. The morphology of the hollow fibers is examined by scanning electron microscopy (SEM). The inner surface of the hollow fibers is studied by X-ray photoelectron spectroscopy (XPS), and it is found that water permeation through the hollow fiber membranes is facilitated due to the change in morphology upon the addition of the PSSNa/EG additive system, but not by the presence of hydrophilic sulfonic acid groups on the membrane surface.
RESUMEN
It is generally accepted that the melting point of a semicrystalline polymer is associated with the thickness of the crystalline lamellae (Gibbs-Thomson equation). In this study, a commercially available multiblock copolymer PolyActive composed of 77 wt % of poly(ethylene glycol terephthalate) and 23 wt % of poly(butylene terephthalate) was dip-coated on top of a multilayer microporous support. The thickness was changed between 0.2 and 8 µm using coating solutions containing 0.75-7.5 wt % PolyActive. The surface temperature of the membrane during dip-coating was monitored using an infrared camera. Single gas permeances of N2, H2, CH4, and CO2 were measured between 20 and 80 °C at temperature steps of 2 °C. Spherulitic superstructures composed of radially directed lamellae were observed in the polarized light microscope in the prepared membranes. Atomic force microscopy studies showed that the thickness of the crystalline lamellae was in the order of 10 nm or 0.01 µm at the surface of the membrane. Therefore, according to the Gibbs-Thomson equation, the melting point should not change in the thickness range 0.2-8 µm. However, the gas permeance data showed that the melting point of the polyether domains of the 0.2 µm PolyActive layer was 10 °C lower compared to that of the 8 µm layer. The results can be explained by considering that the width of many crystalline lamellae significantly reduces as a function of film thickness, thereby reducing the average fold surface free energy/lateral surface free energy ratio.
RESUMEN
Despite the need for sophisticated instrumentation, breath figure assembly (BFA) methods are restricted to produce macroporous films on a tiny scale so far. The current study narrates the fabrication of macroporous films in hollow fiber geometry which extends to adopt the method for continuous production of isoporous surfaces from commercially available low-priced polymer materials. The fabrication of the films in the hollow fiber geometry is carried out by a co-centric quadruple orifice spinneret through which four different liquids are co-extruded simultaneously: bore fluid (to fill the lumen of the fiber), support layer solution, glycerol, and an isoporous film forming solution through the outer most orifice. The extruded entities plunge into a coagulation bath after passing a definite air gap. The implementation of the concept of diffuse-in, droplet formation, and then condense-out behavior of glycerol in a co-extrusion method of hollow fiber spinning makes macroporous film formation possible in an interminable way sidestepping the use of breath figure assembly method. Moreover, the continuous film formation by the proposed mechanism is also authenticated in flat sheet geometry by employing two casting blades in a casting machine. The structure of the films is analyzed by scanning electron microscopy (SEM).
RESUMEN
Nanoporous membranes with tailored size pores and multifunctionality derived from self-assembled block copolymers attract growing interest in ultrafiltration. The influence of the structure of block copolymer in the membrane casting solution on the formation of integral asymmetric isoporous block copolymer membranes using the nonsolvent induced phase separation process (NIPS) has been one of the long-standing questions in this research area. In this work we studied the principal role of the solvent on the micellization and self-assembly of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers by using a combination of dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Our results indicate a significant effect of the solvent selectivity on the optimal casting concentration and solution structure. In addition, morphological characterization of the resulting membranes demonstrates considerable influence of the solvent system on the ordering and uniformity of the pores and pore characteristics in the separation layer as well as porous substructure of the final membranes.
RESUMEN
In this paper; we compare double hydrophobic polystyrene-b-poly(solketal methacrylate) (PS-b-PSMA) and amphiphilic polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) diblock copolymer membranes which are prepared by combining the block copolymer self-assembly in solution with a non-solvent induced phase separation (SNIPS). Diblock copolymers (i.e., PS-b-PSMA) were synthesized by sequential living anionic polymerization, whereas polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) were obtained by acid hydrolysis of the acetonide groups of the polysolketal methacrylate (PSMA) blocks into dihydroxyl groups (PGMA). Membrane structures and bulk morphologies were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); respectively. The resulting PS-b-PGMA diblock copolymers produce an ordered hexagonal cylindrical pore structure during the SNIPS process, while membranes fabricated from the double hydrophobic (PS-b-PSMA) do not under similar experimental conditions. Membrane performance was evaluated by water flux and contact angle measurements.