Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20–40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small-angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by scanning electron microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.     

Compatibilisation of PPE/SAN blends by triblock terpolymers: Correlation between block terpolymer composition, morphology and properties

Immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) with a weight composition of 60/40 were compatibilised by polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) using a two-stage melt-processing approach. In order to investigate the influence of the SBM composition on the compatibilisation efficiency, the block lengths of the triblock terpolymers were systematically varied. The resulting morphological features of the blend systems as function of SBM composition and processing parameters are correlated with the resulting thermal and thermo-mechanical properties. In the ideal case, SBM should be located at the interface as PS is miscible with PPE while PMMA is miscible with SAN. The elastomeric middle block as an immiscible component should remain at the interface. This particular morphological arrangement is known as the ‘raspberry morphology’. A detailed TEM analysis of the blend morphologies following initial extrusion-compounding revealed a high compatibilisation efficiency of the SBM types with equal lengths of the end blocks and, furthermore, the desired raspberry morphology was achieved. In contrast, high PS contents in comparison to the other blocks led to a pronounced micelle formation in the PPE phase. Further evaluation of the blend structures following injection-moulding indicated that the morphologies remain relatively stable during this second melt-processing step. A detailed thermal analysis of all blend systems supports the interpretation of the observed morphological features. The fundamental correlation between SBM composition and blend morphology established in this study opens the door for the controlled development of interfacial properties of such compatibilised PPE/SAN blends during melt-processing.     

Synthesis of complex architectures of comb block copolymers

The synthesis of comb block copolymers by ring opening metathesis polymerization (ROMP), ring opening polymerization (ROP), and atom transfer radical polymerization (ATRP) is described. Block copolymers were synthesized by the ROMP of oxanorbornene and norbornene monomers followed by hydrogenation of the olefins along the backbone. One block of these diblock copolymers possessed initiators either for the ROP of (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione or the ATRP of butyl acrylate. The synthesis and characterization of comb polymers with arms composed of poly(lactic acid) and poly(butyl acrylate) are described. These polymers had well-defined peaks in the size exclusion chromatography spectra which indicated that no homopolymers were synthesized. A comb block copolymer with polymeric arms of poly(styrene-b-vinylpyridine) is described. Vinylpyridine was polymerized from a comb polymer with poly(styrene) arms by ATRP at high dilution of the comb polymer.     

Synthesis of ABA triblock copolymer of poly(potassium acrylate-styrene-potassium acrylate) by atom transfer radical polymerization and the self-assembly in selective solvents

A series of well-defined ABA triblock copolymers of poly(methyl acrylate)-polystyrene-poly(methyl acrylate) (PMA-b-PS-b-PMA) with different molecular weights were synthesized using Cl-PS-Cl as macroinitiator, CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system via atom transfer radical polymerization (ATRP). Amphiphilic triblock copolymer poly(potassium acrylate)-polystyrene-poly(potassium acrylate) (PKAA-b-PS-b-PKAA) was obtained by hydrolyzing PMA-b-PS-b-PMA. The self-assembly behavior of the triblock copolymers in organic solutions, which is a good solvent for the PS block and in aqueous solutions, which is a good solvent for the PKAA blocks was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles obviously increases with increase in molecular weight of triblock copolymers, and the micelles in organic solutions are relatively more stable than in aqueous solutions. The effect of the length of PS block on the Z-average size of the micelles is more obvious in organic solution than in aqueous solution. The morphology of triblock copolymers PKAA-b-PS-b-PKAA in aqueous solution, which is a nearly ‘pearl-necklace’-like shape, was examined by transmission electron microscopy (TEM) at room temperature.     

Enabling nanotechnology with self assembled block copolymer patterns

Block copolymers (BCPs) have received great attention for the past 40 years but only within the past decade have they been seriously considered for nanotechnological applications. Their applicability to nanotechnology stems from the scale of the microdomains and the convenient tunability of size, shape, and periodicity afforded by changing their molecular parameters. The use of the tensorial physical properties of BCPs in such areas as transport, mechanical, electrical, and optical properties will provide substantial benefits in the future. In this review article, we first focus on the current efforts to utilize BCPs in nanotechnologies including nanostructured membranes, BCP templates for nanoparticle synthesis, photonic crystals, and high-density information storage media. In order to realize these applications, control over microdomain spatial and orientational order is paramount. This article reviews various methods to control BCP microdomain structures in the bulk state as well as in thin films. A variety of biases such as mechanical flow fields, electric fields, temperature gradients, and surface interactions can manipulate the microstructures of BCPs. A particular emphasis is made on two approaches, epitaxy and graphoepitaxy, and their combinations. Manipulation of BCP microdomain structures employing multiple external fields promises realization of many potential nanotechnological applications.     

Polymeric micelles formed by polypeptide graft copolymer and its mixtures with polypeptide block copolymer

Polymeric micelles based on poly(γ-benzyl-l-glutamate)-poly(ethylene glycol) graft copolymer (PBLG-g-PEG) with various degrees of grafting and the mixtures composed of PBLG-g-PEG and poly(γ-benzyl-l-glutamate)-poly(ethylene glycol) block copolymer (PBLG-b-PEG) were prepared by the dialysis method in deionized water. Fluorescence spectroscopy and transmission electron microscope (TEM) have been used to study the self-assembly behavior. The experimental results revealed that the degree of grafting exerts marked effect on the critical micelle concentration (CMC) and the morphology of the micelle formed by PBLG-g-PEG. With increasing the degree of grafting, the CMC value becomes larger and the morphology of formed micelle changes from irregular shape to spindle. It was also found that mixtures of PBLG-g-PEG/PBLG-b-PEG can associate into hybrid polymeric micelle with various shapes.     

Controlled organization of self-assembled rod-coil block copolymer micelles

Spherical micelles of a series of poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS) rod-coil diblock copolymers in a selective solvent can organize into large mono-layered films with a well-ordered hexagonal packing of the spheres after solvent evaporation. Organized domains in the spherical micelle film were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The core-shell structure of the spherical micelle remained after solvent evaporation. The micelle diameter in the ordered film as observed by TEM and AFM agree. The size of the spherical micelles can be controlled by the length of PMPCS when the length of the PS is fixed. The sphere diameters were varied from several tens of nanometers to more than one hundred nanometers. Solutions of smaller micelle spheres formed less ordered films than those from larger micelle particles. Additionally, monolayer films of cylindrical worm-like micelles were also prepared. Those cylindrical micelles were observed to be end-capped by spherical micelles. The monolayer micelle film from the largest spherical micelles appeared red when observed in optical microscopy in the reflection mode. A broad adsorption peak with a maximum adsorption wavelength of 545 nm was observed via UV-Vis spectroscopy.     

Asymmetric morphology from an organic/organometallic block copolymer

Block copolymer self-assembly is a burgeoning subject in polymer and materials science driven by both fundamental and applied inspirations. Whereas the vast majority of block copolymer studies have focused on highly symmetric morphologies, here we report the first observation of an unusual asymmetric cylindrical phase in thick films of an organic/organometallic block copolymer, poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS). Microscopy and X-ray scattering data establish the lack of symmetry in this structure and reveal an unusual 3-D network organization. Following selective removal of the PS matrix, the remaining nanoporous film has characteristics of potential value in separation applications such as substantial interconnection (mechanical strength), uniform pore size, and chemical and physical stability.     

An atomic force microscopy study of ozone etching of a polystyrene/polyisoprene block copolymer

The ozone etching of a commercial poly(styrene)/poly(isoprene) (PS/PI) block copolymer (Kraton D1117) was studied by atomic force microscopy. The copolymer contains 17% PS and forms a cylindrical phase in the melt. The copolymer dewetted when spin coated onto a silicon wafer but the film was stable on a grown silicon oxide layer. The structure of the stripe pattern formed was examined on substrates with different oxide layer thicknesses (surface energies). Finally etching by ozone was investigated. For low ozone doses, no degradation of polymer was observable. Extended ozone treatment resulted in more obvious degradation, but the etching was non-selective.     

Selective swelling of polysulfone/poly(ethylene glycol) block copolymer towards fouling-resistant ultrafiltration membranes

Fouling resistance of ultrafiltration (UF) membranes is critical for their long-term usages in terms of stable performance, so convenient approaches to prepare fouling-resistant membranes are always anticipated. Herein, we demonstrate the facile fabrication of antifouling polysulfone-block-poly(ethylene glycol) (PSF-b-PEG, SFEG) composite membranes. SFEG layer was coated onto macroporous supports and cavitated by immerging them in acetone/n-propanol following the mechanism of selective swelling induced pore generation. Thus-produced SFEG membranes possessed high permeance and excellent mechanical strength. Meanwhile, the structures and separation performances of the SFEG layers can be continuously tuned through simply changing swelling durations. More importantly, the hydrophilic PEG chains were spontaneously enriched onto the pore walls through swelling treatment, endowing intrinsic antifouling property to the SFEG membranes. Bovine serum albumin (BSA)/humic acid (HA) fouling tests proved the prominent fouling resistance of SFEG membranes, and the fouling resistance is expected to be long-standing because of the firm connection between PEG chains and PSF matrix by covalent bonding.     

Novel ultrafiltration membranes with adjustable charge density based on sulfonated poly(arylene ether sulfone) block copolymers and their tunable protein separation performance

A novel poly(arylene ether sulfone) (PAES) block copolymer was prepared from previously synthesized fluoride terminated oligomer (A₁₆) and hydroxyl terminated oligomer (B₁₂) by aromatic nucleophilic substitution polycondensation reaction. PAES was subsequently sulfonated under controlled conditions to yield a copolymer (S-PAES) with sulfonic acid groups selectively in the B₁₂ segments and without chain degradation. Non-solvent induced phase separation method was used to prepare a series of ultrafiltration membranes from blends of S-PAES and PAES with varied ratios and, hence, sulfonic acid group densities. Porous membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Studies of membrane performance revealed systematically increasing water permeabilities and reduced protein fouling tendencies with increasing fraction of S-PAES in the membrane. The protein transmission as function of pH value (and hence protein charge) was studied for two model proteins (bovine serum albumin and lysozyme) and found to be controlled by combined size exclusion and charge effects. The selectivity for the separation of the binary protein mixture could be systematically increased with increasing membrane charge density (by increasing S-PAES fraction). Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome. Due to their high stability and tunable functionality, the PAES block copolymers have also large potential as membrane material for other applications.     

两亲嵌段共聚物的合成及其自组装研究进展

作者介绍了两亲嵌段共聚物的活性阴离子聚合、基团转移聚合、开环歧化聚合、活性阳离子聚合、活性／可控自由基聚合、缩聚法、嵌段共聚物化学改性法等合成方法,并对其自组装形成聚合物纳米胶束的制备方法、形成机理以及在药物控制释放领域的应用进行了综述,并对其未来发展趋势进行了展望。     

Enhanced permeation performance of polyether-polyamide block copolymer membranes through incorporating ZIF-8 nanocrystals

Membrane-based CO2 separation is a promising alternative in terms of energy and environmental issues to other conventional techniques.Polyether-polyamide block copolymer (Pebax) membranes are promising for CO2 separation because of their excellent selectivity,but limited by their moderate gas permeability.In this study,fresh-prepared zeolitic imidazolate framework-8 (ZIF-8) nanocrystals were integrated into the Pebax(R)1657 matrices to form mixed matrix membranes.The resulting membrane exhibits significantly improved CO2 permeability (as high as 300％ increase),without the sacrifice of the selectivity,to the pristine polymer membrane.Several physical characterization techniques were employed to confirm the good interfacial interaction between ZIF-8 fillers and Pebax matrices.The effect of added ZIF-8 fillers on the transport mechanism through MMMs is also explored.Mixed-gas permeation for both CO2/N2 and CO2/CH4 was also evaluated.The separation performance for CO2/CH4 mixtures on the ZIF-8/Pebax MMMs is very close to the Roberson upper bound,and thus is technologically attractive for purification of natural gas.     

Superior effect of TEMPO-oxidized cellulose nanofibrils (TOCNs) on the performance of cellulose triacetate (CTA) ultrafiltration membrane

Cellulose triacetate (CTA) ultrafiltration membranes were prepared via phase inversion technique using hydrophilic TEMPO-oxidized cellulose nanofibrils (TOCNs) as modifying agents. The permeation performance of the prepared membranes was evaluated in terms of pure water flux (Ji), protein rejection (Rm) and flux recovery ratio (FRR). Membrane surface morphology and cross-sectional structures were characterized by atomic-force microscopy (AFM) and scanning electron microscopy (SEM), respectively. XRD was performed in order to investigate the interactions between membrane components. Meanwhile, the effects of TOCN concentration on hydrophilicity of the membrane surface and mechanical properties were also examined. The experimental results indicated that CTA/TOCN composite membranes exhibit significant differences in surface properties and intrinsic properties due to the addition of TOCNs.     

Synthesis and performance evaluation of carboxyl-rich low phosphorus copolymer scale inhibitor

A novel low phosphorus terpolymer scale inhibitor P(IA-MA-SHP) was prepared by aqueous free radical polymerization using itaconic acid (IA), maleic acid (MA), and sodium hypophosphite (SHP) as raw materials. It was mainly used as an efficient scale inhibitor to inhibit CaCO₃. The structures of the copolymers were characterized by Fourier transform infrared, ¹H-NMR, and ¹³C-NMR, and the thermal properties, and scale sample crystal structure morphology of the copolymers were analyzed by thermogravimetric analysis, x-ray diffraction (XRD), and scanning electron microscope (SEM). The effects of dosage, monomer ratio, temperature, and reaction time on the scale inhibition effect were investigated, and the optimal synthesis conditions were determined. The results show that: when the monomer ratio is n(IA):n(MA) = 1.0:1.0, the mass fraction of SHP is 10%, the amount of ammonium persulfate initiator is 12%, the reaction temperature is 90°C, and the reaction time is 4 h, when the dosage of the agent is 20 mg L⁻¹, the scale inhibition rate of CaCO₃ is 94.30%, while it also has a favorable inhibitory effect on CaSO₄. The results of SEM and XRD show that the copolymer scale inhibitor can distort the lattice and has a favorable adsorption and dispersion effect. In addition, it has a positive effect on controlling the scale.     

Effects of ultrasound parameters on ultrasound-assisted ultrafiltration using cross-flow hollow fiber membrane for Radix astragalus extracts

In this study, the effects of ultrasonic parameters on permeate flux and fouling resistances in the ultrasound-assisted ultrafiltration (UAUF) process of Radix astragalus extracts with hollow fiber membrane (HFM) was investigated. Ultrasonic parameters such as frequency, power and irradiation mode all can significantly affect the flux and fouling during the UAUF process, though the ultrasound power intensity was attenuated to be 10% only from generator. Concentration polarization and cake layer were decreased effectively by the ultrasound irradiation, resulting in a high flux performance. Meanwhile, HFM was susceptible to the irradiation at high power and low frequency compared with a flat sheet membrane. Ultrasound can not only enhance the permeate flux in UAUF but also cause breakage of HFM at an unsuited ultrasound field. It can be applied to the ultrafiltration process with HFM at an appropriate power and frequency.     

Preparation and antifouling performance of thin inorganic ultrafiltration membrane via assisted sol-gel method with different composition of dual additives

A novel TiO₂ thin film was prepared on the ceramic hollow fiber by the sol-gel method using poly(vinylpyrrolidone) (PVP) and polyvinyl alcohol (PVA) as additives. SEM images verified the formation of TiO₂ layer with various thickness using different composition of titania sols. The effect of the PVP and PVA contents on the TiO₂ sol properties, the separation and the antifouling performance of the ultrafiltration membranes were investigated thoroughly. When the contents of PVP and PVA were 1.0 wt% and 0.8 wt%, respectively, the resultant membrane showed a thickness of 0.55 μm with a pure water flux of 255 L m^?2 h^?1. In addition, the adherent foulant bovine serum albumin was applied to evaluate the antifouling performance. During the three fouling-recovery cycles, the flux recovery ratio and the flux decay ratio maintained about 99% and 30%. The BSA flux and rejection were still 169 L m^?2 h^?1 and 96.9% after the cycles, indicating a superior antifouling property.     

不锈钢膜技术处理高浓度乳化废水的研究

采用不锈钢金属膜(以下简称不锈钢膜)分离技术处理乳化废液。在实验研究中,探讨了各参数对处理效果的影响,着重考察了压力、膜孔径、浓缩倍数、进水浓度等各影响因素对COD去除效果的影响,由此确定适合的运行条件,最佳工艺参数为:膜孔径选定为0.1μm,最佳操作压力为0.35MPa,最佳操作温度为45℃;经过不锈钢膜过滤和纳滤处理后的乳化废液具有良好的可生化性,适合采用生化方法做进一步处理。     

Preparation and characterization of Al3+-doped TiO2 tight ultrafiltration membrane for efficient dye removal

Al³⁺-doped TiO₂ (AT) tight ultrafiltration membrane with stable anatase phase was prepared by a modified sol-gel process using butyl titanate and aluminum chloride as the precursor and aluminum source respectively. The removal of Alizarin red-S was investigated by filtration experiment. A dip-coating process on homemade flat Al₂O₃ intermediate layer by TiO₂ sol followed by heat treatment was adopted to obtain the desired AT membrane. The addition of Al³⁺ inhibits the phase transformation of nanosized TiO₂ from anatase to rutile and restrains the growth of crystallite, resulting in the pore size of the separation layer reducing to 3.5 nm. The prepared AT1-500 membrane exhibits enhanced hydrophilicity with no cracks or pinholes, and shows a water permeability of 9.6 L m^-2 h⁻¹ bar⁻¹ and cut-off molecular weight (MWCO) of 4650 Da. The membrane demonstrated a retention rate of 96.9% for Alizarin Red-S (250 ppm) and maintained almost constant under repeated using.