New variations of the old ‘phase inversion” process: SNIPS, CIPS , DIPS and more

The non-solvent induced phase separation (NIPS) and also the drying induced phase separation (DIPS) for membrane formation is since its first description by Zsigmondi and Bechold nearly 100 years old. But the process is still young and nearly weekly we see new formulations for novel membrane structures. This membrane formation method gets especially interesting when combined with additional physical or chemical processes. The non-solvent induced phase separation can be coupled with self-assembly of nanometer-sized colloidal micelles resulting in asymmetric membranes with pores down to 2 nanometer; or the NIPS process can be accompanied by metal complexation or chemical reactions leading to skinned membranes with unique properties. When the drying induced phase separation invented by Zsigmondi and Bechold is applied to concentrated block copolymer solutions complex asymmetric structures with a hierarchical pore structures can evolve. A new generation of membranes with unique properties can be manufactured using these “hybrid” formation methods. Recent developments and challenges will be introduced and discussed in this lecture

Polydopamine mediated self-cleaning of high-flux pH-responsive isoporous membranes for filtration applications

A major challenge in membrane filtration is fouling which reduces the membrane performance. The fouling is mainly due to the adhesion of foulants on the membrane surfaces. In this work, we studied the fouling behavior of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) isoporous membrane and the mussel inspired polydopamine/L-Cysteine isoporous zwitterionic membrane. The polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) isoporous membrane was fabricated via self-assembly and non-solvent induced phase separation.1 Subsequently, the isoporous membrane was modified through a mild mussel-inspired polydopamine (PDA) coating by retaining the isoporous morphology and water flux.2 Furthermore, zwitterionic L-Cysteine was anchored on the PDA layer coated membranes via Michael addition reaction at neutral pH and 50oC. The membranes were thoroughly characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and zeta potential measurements. The contact angle and dynamic scanning calorimetry (DSC) measurements were carried out to examine their hydrophilicity. The pH-responsive behaviour of the modified membrane remains unchanged and the antifouling ability after PDA/L-Cysteine functionalization was improved. The modified and unmodified isoporous membranes were tested using humic acid and natural organic matter contaminated solutions at 0.5 bar feed pressure. References Peinemann, K.-V.; Abetz, V.; Simon, P. F. W. Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation. Nat. Mater. 2007, 6, 992–996. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science. 2007, 318, 426–430

Novel adsorptive ultrafiltration membranes derived from polyvinyltetrazole-co-polyacrylonitrile for Cu(II) ions removal

Novel adsorptive ultrafiltration membranes based on polyvinyltetrazole-co-polyacrylonitrile polymer were manufactured for an efficient copper removal. [Display omitted] •Polyvinyltetrazole (PVT)-co-PAN based ultrafiltration membranes were fabricated.•PVT segment played a significant role for copper adsorption.•The binding capacity of PVT–PAN membranes for Cu(II) ions exceeded 130mgg−1.•Copper loaded membranes could be regenerated with 0.25mM EDTA solution. Novel adsorptive ultrafiltration membranes were manufactured from synthesized polyvinyltetrazole-co-polyacrylonitrile (PVT-co-PAN) by nonsolvent induced phase separation (NIPS). PVT-co-PAN with various degree of functionalization (DF) was synthesized via a [3+2] cycloaddition reaction at 60°C using a commercial PAN. PVT-co-PAN with varied DF was then explored to prepare adsorptive membranes. The membranes were characterized by surface zeta potential and static water contact angle measurements, scanning electron microscopy as well as atomic force microscopy (AFM) techniques. It was shown that PVT segments contributed to alter the pore size, charge and hydrophilic behavior of the membranes. The membranes became more negatively charged and hydrophilic after addition of PVT segments. The PVT segments in the membranes served as the major binding sites for adsorption of Cu(II) ions from aqueous solution. The maximum adsorption of Cu(II) ions by the membranes in static condition and in a continuous ultrafiltration of 10ppm solution was attained at pH=5. The adsorption data suggest that the Freundlich isotherm model describes well Cu(II) ions adsorption on the membranes from aqueous solution. The adsorption capacity obtained from the Freundlich isotherm model was 44.3mgg−1; this value is higher than other membrane adsorption data reported in the literature. Overall, the membranes fabricated from PVT-co-PAN are attractive for efficient removal of heavy metal ions under the optimized conditions

PEG modified poly(amide-b-ethylene oxide) membranes for CO2 separation

In the present work, membranes from commercially available Pebaxr MH 1657 and its blends with low molecular weight poly(ethylene glycol) PEG were prepared by using a simple binary solvent (ethanol/water). Dense film membranes show excellent compatibility with PEG system up to 50 wt.% of content. Gas transport properties have been determined for four gases (H2, N2, CH4, CO2) and the obtained permeabilities were correlated with polymer properties and morphology of the membranes. The permeability of CO2 in Pebaxr/PEG membrane (50 wt.% of PEG) was increased two fold regarding to the pristine Pebaxr. Although CO2/N2 and CO2/CH4 selectivity remained constant, an enhancement of CO2/H2 selectivity was observed. These results were attributed to the presence of EO units which increases CO2 permeability, and to a probable increase of fractional free-volume. Furthermore, for free-volume discussion and permeability of gases, additive and Maxwell models were used

Pebax/Polyethlylene glycol blend thin film composite membranes for CO2 separation: Performance with mixed gases

The paper describes the performance of Pebax©/Polyethylene glycol (PEG) blend thin film composite membranes for CO2 separation from gas mixtures containing H2, N2 and CH4. Membranes were tested at different conditionstemperature andpressure dependence of gas flux and selectivity were explored. The temperature dependence was correlated with the Arrhenius equation to determinethe activation energy of single gas permeation. Single and mixed gas permeation was measured for different pressures at 293K up to 20 bar. Improvedpermeabilities and CO2/H2 selectivities were obtained in the newly developed composite membranes

Complexation-Induced Phase Separation: Preparation of Composite Membranes with a Nanometer-Thin Dense Skin Loaded with Metal Ions

We present the development of a facile phase-inversion method for forming asymmetric membranes with a precise high metal ion loading capacity in only the dense layer. The approach combines the use of macromolecule-metal intermolecular complexes to form the dense layer of asymmetric membranes with nonsolvent-induced phase separation to form the porous support. This allows the independent optimization of both the dense layer and porous support while maintaining the simplicity of a phase-inversion process. Moreover, it facilitates control over (i) the thickness of the dense layer throughout several orders of magnitude from less than 15 nm to more than 6 μm, (ii) the type and amount of metal ions loaded in the dense layer, (iii) the morphology of the membrane surface, and (iv) the porosity and structure of the support. This simple and scalable process provides a new platform for building multifunctional membranes with a high loading of well-dispersed metal ions in the dense layer

Complexation-Tailored Morphology of Asymmetric Block Copolymer Membranes

Hydrogen-bond formation between polystyrene-<i>b</i>-poly (4-vinylpyridine) (PS-<i>b</i>-P4VP) block copolymer (BCP) and −OH/–COOH functionalized organic molecules was used to tune morphology of asymmetric nanoporous membranes prepared by simultaneous self-assembly and nonsolvent induced phase separation. The morphologies were characterized by field emmision scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Hydrogen bonds were confirmed by infrared (IR), and the results were correlated to rheology characterization. The OH-functionalized organic molecules direct the morphology into hexagonal order. COOH-functionalized molecules led to both lamellar and hexagonal structures. Micelle formation in solutions and their sizes were determined using dynamic light scattering (DLS) measurements and water fluxes of 600–3200 L/m²·h·bar were obtained. The pore size of the plain BCP membrane was smaller than with additives. The following series of additives led to pores with hexagonal order with increasing pore size: terephthalic acid (COOH-bifunctionalized) < rutin (OH-multifunctionalized) < 9-anthracenemethanol (OH-monofunctionalized) < 3,5-dihydroxybenzyl alcohol (OH-trifunctionalized)