Volkan Filiz

Formation of Integral Asymmetric Membranes of AB Diblock and ABC Triblock Copolymers by Phase Inversion

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.

Thin Isoporous Block Copolymer Membranes: It Is All about the Process.

The combination of the self-assembly of amphiphilic block copolymers and the nonsolvent induced phase inversion process offers an efficient way to isoporous integral-asymmetric membranes. In this context we report fast, easily upscalable and material reducing ways to thin self-assembled membranes. Therefore, we succeeded to implement a spray or dip coating step into the membrane formation process of different diblock copolymers like polystyrene-block-poly(4-vinylpyridine), poly(α-methylstyrene)-bock-poly(4-vinylpyridine), and polystyrene-block-poly(iso-propylglycidyl methacrylate). The formation of hexagonal pore structures was possible using a highly diluted one solvent system allowing the reduction of diblock copolymer consumption and therefore the production costs are minimized compared to conventional blade casting approaches. The broad applicability of the process was proven by using different flat and hollow fiber support materials. Furthermore, the membranes made by this new method showed a more than 6-fold increase in water flux compared to conventional polystyrene-block-poly(4-vinylpyridine) membranes with similar pore sizes prepared by blade casting. The membranes could be proven to be stable at transmembrane pressures of 2 bar and showed a pH responsive flux behavior over several cycles.

Carbohydrates as additives for the formation of isoporous PS-b-P4VP diblock copolymer membranes.

Highly porous polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer membranes are prepared using carbohydrates as additives. Therefore α-cyclodextrine, α-(D)-glucose, and saccharose (cane sugar) are tested for the membrane formation of three different PS-b-P4VP polymers. The addition of the carbohydrates leads to an increasing viscosity of the membrane solutions due to hydrogen bonding between hydroxyl groups of the carbohydrates and pyridine units of the block copolymer. In all cases, the membranes made from solution with carbohydrates have higher porosity, an improved narrow pore distribution on the surface and a higher water flux as membranes made without carbohydrates with the same polymer, solvent ratio, and polymer concentration.

Continuous Equilibrated Growth of Ordered Block Copolymer Thin Films by Electrospray Deposition

Deposition of block copolymer thin films is most often accomplished in a serial process where material is spin coated onto a substrate and subsequently annealed, either thermally or by solvent vapor, to produce a well-ordered morphology. Here we show that under appropriate conditions, well-ordered block copolymer films may be continuously grown under substrate equilibrated conditions by slow deposition of discrete subattoliter quantities of material using electrospray. We conduct time-resolved observations and investigate the effects of process parameters that underpin film morphology including solvent selectivity, substrate temperature, block-substrate selectivity, and flow rate of the feed solution. For a PEO cylinder-forming poly(styrene-b-ethylene oxide) block copolymer, we uncover a wide temperature window from 90 to 150 °C and an ideal flow rate of 2 μL/min for ordered film deposition from dilute acetone solutions. PEO cylinders aligned with their long axes perpendicular to the film-air interface at optimal spray conditions. Using poly(styrene-b-methyl methacrylate) deposited onto neutrally selective surfaces, we show that the substrate-equilibrated process results in vertically oriented microdomains throughout the film, indicating a preservation of the initial substrate-dictated morphology during the film deposition. Electrospray offers a new and potentially exciting route for controlled, continuous growth of block copolymer thin films and manipulation of their microstructure.

Pyrene-POSS nanohybrid as a dispersant for carbon nanotubes in solvents of various polarities: its synthesis and application in the preparation of a composite membrane

In this study we report the preparation of nanohybrid dispersant molecules based on pyrene and polyhedral oligomeric silsesquioxanes for non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs). The prepared dispersant improves the dispersion of MWCNTs in organic solvents with very different polarities such as tetrahydrofuran, toluene, and n-hexane. The functionalized MWCNTs were used to introduce conductivity into polydimethylsiloxane membranes which can be used for electrostatic discharge applications.

Influence of Poly(ethylene glycol) Segment Length on CO2 Permeation and Stability of PolyActive Membranes and Their Nanocomposites with PEG POSS.

Three grades of PolyActive block copolymers are investigated for CO2 separation from light gases. The polymers are composed of 23 wt % poly(butylene terephthalate) (PBT) and 77 wt % poly(ethylene glycol terephthalate) (PEGT) having the poly(ethylene glycol) segments of 1500, 3000, and 4000 g/mol, respectively. A commercial PEG POSS (poly(ethylene glycol) functionalized polyoctahedral oligomeric silsesquioxanes) is used as a nanofiller for these polymers to prepare nanocomposites via a solvent casting method. Single gas permeabilities of N2, H2, CH4, and CO2 are measured via the time-lag method in the temperature range from 30 to 70 °C. The thermal transitions of the prepared membranes are studied by differential scanning calorimetry (DSC). It is found that the length of PEG segment has a pronounced influence on the thermal transition of the polymers that regulates the gas separation performance of the membranes. The stability of the nanocomposites is also correlated with the thermal transition of the polyether blocks of the polymer matrices.

Protein separation performance of self-assembled block copolymer membranes

A comprehensive study of the separation performance of highly porous self-assembled integral asymmetric block copolymer membranes was carried out. Four different polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers were used to prepare membranes with pore sizes increasing with the molecular weight of the polymers. The pore sizes vary from 17 nm to 53 nm. Clean water fluxes and the adsorption of lysozyme, myoglobin, haemoglobin, catalase and ferritin on the membranes were studied. Diffusion rates of the proteins were examined and selectivities are discussed. The membranes show promising results regarding the separation of different proteins in the range of around four to twelve nm. The characteristics of PS-b-P4VP diblock copolymer membranes were compared with a commercially available polycarbonate track-etched membrane.

Covalent Attachment of Polymersomes to Surfaces

We show that vesicles made of block copolymers with aldehyde end groups can be covalently attached to aminated and non-aminated, untreated glass surfaces. The attached vesicles were sufficiently stable to allow a detailed investigation of vesicle shapes by confocal laser scanning microscopy (CLSM) and AFM in aqueous solutions allowing reconstruction of 3D images of the vesicle structure. Covalently attached PCL-PEO, PLA-PEO, and PI-PEO block copolymer vesicles have different footprint areas and different shapes due to their differences in bilayer stiffness.

Synthesis, characterization and gas permeation properties of anthracene maleimide-based polymers of intrinsic microporosity

A series of new monomers containing dialkyl anthracene maleimide derivatives [4a,b(I–V)], which can be used as a precursor of a polymer of intrinsic microporosity (PIM) has been synthesized and characterized successfully. The homopolymers prepared via polycondensation with 2,3,5,6,-tetrafluoroterephthalonitrile (TFTPN) and their copolymers in combination with 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) were characterized by SEC, FT-IR, TGA, 1H-NMR, BET-surface area and gas transport properties. Compared to polymers derived from 4a(I–V) monomers, the homopolymers and copolymers obtained from 4b(I–V) show improved solubility in common organic solvents and have high average molecular weight. Therefore they are able to form robust and transparent films. The gas transport properties of homopolymers and copolymers of 4b(I–V) show enhanced selectivity compared to PIM-1 for gas pairs such as O2/N2, CO2/N2 and CO2/CH4, followed by a slight decrease in permeability. The introduction of anthracene maleimide units (especially 4bIII) in the copolymer leads to more efficient chain packing and gives the copolymer a similar pore width distribution as PIM-1. As a consequence, the introduction of anthracene maleimide enhanced the CO2 selectivity of copolymers, compared to previously reported film forming polymers. Therefore, these polymers might be useful for gas separations relying on CO2 selectivity.

Poly(ether–amide) vs. poly(ether–imide) copolymers for post-combustion membrane separation processes

This work is focused on the comparison between the commercial polyamide PEBAX® MH 1657 and a new set of synthetized polyimides with different polyethylene glycol lengths. The samples were synthesized with the same poly(ethylene oxide) (PEO) content (57 wt%) for comparison with the commercial polymer. All polymers have been characterized by several techniques revealing a direct relationship between crystallinity, PEO length and permeability properties. Results at temperatures lower than the Tm of the polyether blocks confirm that lower PEO crystallinity corresponds to higher permeability. At temperatures higher than the Tm of the PEO block, no significant differences were found between the commercial polyamides and the synthesized polyimides. This confirms that the aliphatic phase controls the separation while the hard block provides mechanical strength. Remarkable are the results for the CO2/N2 separation. These new copolyimides are promising materials for post-combustion processes.