Non-solvent Induced Phase Separation Process Research Articles

Advanced nanofiltration membrane fabricated on the porous organic cage tailored support for water purification application

The support layer have been recently recognized as an important factor in tailoring the performance of thin film composite membranes, but until now limited methods are available to optimize the support properties for the fabrication of high-performance nanofiltration (NF) membrane. Herein, Noria, one kind of porous organic cages, was employed as the filler to prepare Noria hybrid polysulfone (PSF) support through non-solvent-induced phase separation (NIPS). Owing to its good solubility in N-methylpyrrolidone, the blended Noria could distribute in the dope solution homogeneously and the structure and surface properties of the resulting support were finely tuned. Assisted from the inner cavity of Noria as well as enhanced hydrophilicity, the pure water flux of support membrane with a Noria loading of 3.60 wt% reached 125 L m−2 h−1 bar−1, which was nearly 2.5-fold higher than the pristine one. In addition to that entrapped in the PSF chains, a mass of Noria molecules aggregated on support surface during the NIPS process and they could be further etched by alkaline solution, in situ enlarging the surface pore size. After the interfacial polymerization (IP), the NF membrane fabricated on the etched support depicted excellent performance compared with those incorporated with other fillers either in the support or in the polyamide layer. Furthermore, this study could promote the understanding about the role of support in the IP process for the preparation of TFC membranes.

Fabrication of high flux and fouling resistant membrane: A unique hydrophilic blend of polyvinylidene fluoride/polyethylene glycol/polymethyl methacrylate

To overcome the fouling issue of membrane, hydrophilic membrane fabrication is a rich research domain. In this study, hydrophilic membrane was fabricated by incorporating the hydrophilic polymer into dope solution. Polymethyl methacrylate (PMMA) was blended with polyvinylidene fluoride (PVDF) (12%), polyethylene glycol (PEG) (2%), and N,N dimethyl acetamide (DMAc) solution and membranes were prepared by non-solvent induced phase separation process (NIPS). The synthesized membranes were characterized for their surface and cross-sectional morphology, crystallinity, chemical composition, hydrophilicity, pore size, porosity, permeability, pollutant retention, and fouling resistance. The addition of only PEG to PVDF and PMMA to PVDF increased the porosity, pore size and hydrophilicity of the membrane. Whereas, a combination of both PEG (2%) and PMMA (1%) into PVDF further increased the hydrophilicity (contact angle 60°) and porosity (90%) of the membrane. The maximum pure water flux (PWF) (565 LMH) was also recorded with PVDF-PEG-PMMA membrane without compromising the humic acid (HA) retention rate (80%). Moreover, flux recovery ratio of PVDF-PEG-PMMA membrane was more than 80% with hydraulic flushing. The combination of PEG and PMMA proved to be very effective for improving the properties of PVDF membrane resulting in better flux and antifouling potential of the membrane.

A solution for trade-off phenomenon based on symmetric-like membrane with nano-scale pore structure

Outstanding separation properties combining high water permeability and permselectivity have always been a pursuit for porous membranes, which were commonly determined by the membrane structure and surface properties. In this work, PLA membrane with unique nanoscale bicontinuous structure was fabricated by non-solvent induced phase separation (NIPS) process involving in situ crosslinking of glycidyl methacrylate (GMA) monomers in polylactic acid (PLA) casting solution. Afterwards, systematic approaches were carried out to characterize the regulating functions of the in situ formed polymerized GMA (PGMA) on the morphology, pore shape, pore size, porosity, wettability, water flux and solutes rejection of developed PLA membranes. With the addition of GMA monomers, novel bicontinuous interconnected PLA membranes with narrowly distributed nanoscale pores were obtained. These generated PLA membranes presented higher water flux and better selective rejection to various dextran molecular owing to their larger effective pore size and narrower pore size distribution. This study provides an innovative strategy to overcome the trade-off issue when membranes are used for water treatment.

Optimized anti-biofouling performance of bactericides/cellulose nanocrystals composites modified PVDF ultrafiltration membrane for micro-polluted source water purification.

The covalently functionalized cellulose nanocrystal (CNC) composites were synthesized by bonding common bactericides, such as dodecyl dimethyl benzyl ammonium chloride (DDBAC), ZnO and graphene oxide (GO) nanosheets, onto the CNC's surface. Then, the DDBAC/CNC, ZnO/CNC and GO/CNC nanocomposites modified polyvinylidene fluoride (PVDF) ultrafiltration membranes were fabricated by a simple one-step non-solvent induced phase separation (NIPS) process. The resultant hybrid membranes possessed porous and rough surfaces with more finger-like macropores that even extended through the entire cross-section. The hydrophilicity, permeability, antibacterial and antifouling performance and mechanism of the hybrid ultrafiltration membranes were evaluated and compared in detail, aiming at screening a superior hybrid membrane for practical application in micro-polluted source water purification. Among these newly-developed hybrid membranes, GO/CNC/PVDF exhibited an enhanced perm-selectivity with a water flux of 230 L/(m2 h bar) and humic acid rejection of 92%, the improved antibacterial activity (bacteriostasis rate of 93%) and antifouling performance (flux recovery rate (FRR) of >90%) being due to the optimized pore structure, higher surface roughness, incremental hydrophilicity and electronegativity. A lower biofouling level after three weeks' filtration of the actual micro-polluted source water further demonstrated that embedding the hydrophilic and antibacterial GO/CNC nanocomposite into the polymer matrix is an effective strategy to improve membrane anti-biofouling ability.

Amine-Containing Block Copolymers for the Bottom-Up Preparation of Functional Porous Membranes

The remarkable ability of biological systems to specifically recognize, sort, and process molecules encourages the development of novel bio-inspired membranes and interfaces. Herein, we focus on the functionalization of amphiphilic polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) with the amino acid glycine yielding polar block segments with primary amine functionalities. Excellent control over the tailored block copolymer (BCP) synthesis and functionalization is proven by size exclusion chromatography (SEC), 1H solution NMR, and 15N solid state NMR spectroscopy. For the first time, BCPs containing primary amines were used for the self-assembly and non-solvent induced phase separation (SNIPS) process for the preparation of isoporous and integral asymmetric membranes. Hexagonally arranged open pores with diameters of 19 nm were obtained as shown by scanning electron microscopy (SEM), atomic force microscopy (AFM), and pH-dependent water flux measurements. Additionally, the primary amine was...

Ultrafiltration membranes from polymerization of self-assembled Pluronic block copolymer mesophases

Industrially, ultrafiltration (UF) membranes are produced through non-solvent induced phase separation (NIPS), but due to environmental hazards inherent to the NIPS process as well as the low surface porosity and fouling resistance of membranes produced via this method, an alternative route to UF membranes is desirable. This work presents the self-assembly of Pluronic block copolymers in the presence of water and a monomeric phase as a new technique for the preparation of UF membranes without the need for organic solvent or post-modification. Different compositions of block copolymer, water, and monomer were polymerized to obtain both hexagonal and lamellar mesostructures, as indicated by small angle X-ray scattering (SAXS) and cross-polarized light microscopy. As-synthesized membranes were found to have pore sizes in the range of 3–4 nm with a molecular weight cutoff of 1500 g/mol and displayed both excellent fouling resistance and high permeance of water, vastly outperforming a conventional NIPS UF membrane. Further, in contrast to NIPS, the proposed method provides flexibility in terms of both the final membrane chemistry and pore size. As such, it is a versatile approach that can be easily tailored to produce membranes for a wide range of applications including wastewater treatment and food processing.

Influence of CaCO3 pore-forming agent on porosity and thermal conductivity of cellulose acetate materials prepared by non-solvent induced phase separation

Thermal insulation materials with a low thermal conductivity are indeed demanded because they play the main role in the enhancement of energy conservation in various industries, especially lightweight constructive materials. Therefore, tubular cellulose acetate (CA) materials were firstly prepared by non-solvent induced phase separation (NIPS). In the NIPS process, the concentration of CA was varied in a range of 20–40 wt%. Also, the temperature of water used as a non-solvent was studied from 5 °C up to 50 °C. According to the FE-SEM results, the 30 wt% CA solution at 20 °C provides tubular CA materials with a higher porous structure than an original CA material but the pore size is quite larger than the mean free path of air leading to achieve a material with high thermal conductivity. To overwhelmed such a problem, the calcium carbonate (CaCO3) was used to be pore forming agents in order to decrease pore size of prepared CA sheet materials. The amount of CaCO3 particles in the CA sheet materials was varied as 50 and 60 wt% to investigate its effect on porosity and thermal conductivity of the prepared materials. As the results, the CA sheet materials prepared using NIPS process and after removing 60 vol% CaCO3 have an enlargement of pores with a size lower than the mean free path of air. They exhibit high porous materials leading to the reduction of their thermal conductivity, which has the lowest value about 0.043 W/mK. Consequently, the CA materials are potentially applied for constructive materials in order to reduce energy consumption in buildings.

Explorations of combined nonsolvent and thermally induced phase separation (N-TIPS) method for fabricating novel PVDF hollow fiber membranes using mixed diluents

The combination of nonsolvent and thermally induced phase separation (N-TIPS) method has shown promising ability in harvesting the features from the nonsolvent induced phase separation (NIPS) and thermally induced phase separation (TIPS) processes for developing membranes with a tailorable surface pore structure. However, previous approaches have been subjected to either the formation of macrovoids or dense layer due to the dominant NIPS effect, or required sophisticated instruments and operation skills. In this work, a facile attempt was carried out to fabricate novel polyvinylidene fluoride (PVDF) hollow fiber membranes with tunable surface pore structure while maintaining the narrow pore size distribution and mechanical strength. A modified N-TIPS method was developed by using mixed diluents: dimethyl phthalate (DMP) as a water-immiscible poor solvent for TIPS process, and triethyl phosphate (TEP) as a water-miscible neutral solvent to bridge the TIPS and NIPS processes. To further control the membrane formation especially near the membrane surface, an amphiphilic additive Pluronic F127 was also added as a potential pore-former and surface hydrophilicity modifier. PVDF hollow fiber membranes with a highly porous structure and a narrow pore size distribution were successfully synthesized by using TEP and Pluronic F127 in the N-TIPS process. The mechanism of N-TIPS process was thoroughly discussed. The water permeability of the membrane increased significantly from 389 ± 30–922 ± 36 L m–2 h–1 bar–1, with overall porosity improved from 50 ± 2.2–69 ± 2.9%, and a mean pore size of ~ 0.18 µm. The membranes produced by N-TIPS method also exhibited a good tensile strength ranging from 5.6 ± 0.1–6.5 ± 0.2 MPa, showing a great potential for a broad range of water applications after further modifications. Besides, the formation of piezoelectric β-phase crystals of the PVDF membrane was observed when the mixed diluent was used, which sheds light on the possible applications of resultant membranes in electrochemical separation process.

Efficient removal of heavy metal ions based on the selective hydrophilic channels

The hydrophilic channels for water permeation with the selective rejection ability towards heavy metal ions were constructed in a novel forward osmosis (FO) membrane using polyethyleneimine (PEI) and zein, which improved the separation efficiency of the prepared FO membrane and exhibited the expected performance in the treatment of heavy metal ion wastewaters. The PEI/zein active layer was prepared by one-step method at the gas–liquid interface based on the non-solvent induced phase separation process. PEI as a functional medium imparted the significantly improved hydrophilicity, adsorption ability and water permeability on the zein layer. The rejection ability of heavy metal ions by the PEI/zein active layer was significantly improved based on the strong complexation ability of PEI, and the rejection ratios of Cd(II), Ni(II), Pb(II) and Cu(II) ions were more than 97%. In addition, with the preferential occupancy of Cu(II) ions in the water channel of the prepared FO membrane, the rejection ratios of Cd(II), Ni(II) and Pb(II) ions were further improved to be more than 99.5%. The excellent membrane-forming ability and machinability of zein provide a basis for the FO performance improvement via the introduction of functionalities. This paper aims to provide new ideas for the preparation of efficient FO membranes and extend the application scope of the current FO technology.

In-situ modification of PVC UF membrane by SiO 2 sol in the coagulation bath during NIPS process

Polyvinyl chloride (PVC) ultrafiltration (UF) membrane was modified by silica sol in the coagulation bath during non-solvent induced phase separation (NIPS) process. The effects of silica sol concentrations on the morphology, surface property, mechanical strength and separation property of PVC UF membranes were systematically investigated. PVC membranes were characterized by Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), contact angle goniometry and tensile strength measurement. The results showed that silica had been successfully assembled on the surface of PVC UF membrane. With the increase of silica sol concentration in the coagulation bath, the morphologies of PVC UF membranes changed from cavity structure to finger-like pore structure and asymmetric cross-section structure. The hydrophilicity and permeability of PVC UF membranes were further evaluated. When silica sol concentration was 20 wt.%, the modified PVC membrane exhibited the highest hydrophilicity with a static contact angle of 36.5 degree and permeability of 91.8 (L.m-2.h-1). The structure of self-assemble silica had significant impact on the surface property, morphology, mechanical strength and resultant separation performance of the PVC membranes.

PH‐dependent property of carboxyl‐based ultrafiltration membranes fabricated from poly(vinyl chloride‐r‐acrylic acid)

ABSTRACTCarboxyl groups in the membranes usually contribute the hydrophilicity and antifouling properties. However, membrane performance including permeation and separation properties is not stable at different pH environments due to pH sensitivity of carboxyl groups. In this work, a series of membranes from random copolymers poly(vinyl chloride‐r‐acrylic acid) [P(VC‐r‐AA)] were fabricated via nonsolvent induced phase separation process. The morphology and surface properties were investigated. The pH‐dependent property of carboxyl groups contained ultrafiltration membranes were studied in detail. The results indicated that pH sensitivity of these membrane was restrained, which was mainly attributed to the random sequential structure of VC and AA repeating unit in P(VC‐r‐AA) copolymer. The probable arched structures on the pore surface/wall at alkaline environment limited the obvious change of the pore size, which resulted in the stable permeation and separation properties at the varied pH environments. Therefore, it indicated that P(VC‐r‐AA) was a kind of promising membrane material which would be widely applied in water treatment field. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47068.

Preparation of polyvinylidene fluoride blend anion exchange membranes via non-solvent induced phase inversion for desalination and fluoride removal

Non-solvent induced phase inversion is a scalable, cost-effective, and fast process for the preparation of pressure-driven membranes. Despite of the advantages, this process is hitherto unreported in the preparation of ion exchange membranes. Herein, we report the preparation of supported anion exchange membranes of polyvinylidene fluoride (PVDF) blend poly(methyl methacrylate)-co-poly(chloromethyl styrene) (PMMA-co-PCMSt) by the non-solvent induced phase separation process followed by post treatment with tertiary diamine. The obtained membranes were partially crosslinked due to the nucleophilic substitution reaction of diamine with the activated halide groups of the blend membrane. A series of membranes was obtained by changing the PVDF to copolymer ratio. These membranes were used for the desalination as well as removal of fluoride ions via the electrodialysis (ED) process. A membrane prepared with blend containing 69.5%, w/w copolymer and 30.5% w/w PVDF exhibited best electrochemical properties with ion-exchange capacity 1.85 meq g−1, ionic conductivity 3.02 mS cm−1, and transport number 0.98. This AEM also showed 0.978 kWh kg−1 power consumption and 94% current efficiency during desalination of water at 2 V/cell pair applied potential. The AEMs obtained by this process showed good hydrolytic and oxidative stability. This process thus highlights simple and fast preparation of high performance AEMs for water desalination and purification.

Silica/poly(vinylidene fluoride) porous composite membranes for lithium-ion battery separators

Separator membranes based on silica/poly(vinylidene fluoride) composites were prepared by a non-solvent induced phase separation (NIPS) process with different air exposure times before immersion in a water coagulation bath and for the same filler content of 20 wt%. Mesoporous silica spheres (SS) of ~ 400 nm average diameter were synthetized by sol-gel method and dispersed into the polymer matrix.It was demonstrated that the morphology, degree of porosity, uptake value and electrical properties of the composite membranes were influenced by the time of exposure to air and the presence of SS.The membranes were assembled in Li/C-LiFePO4 half-cells and the best cycling performance was obtained for the composite membrane after 1 min exposure to air. This membrane shows an ionic conductivity of 0.9 mS cm−1. Moreover, at a very high rate of 2 C and after 50 cycles, the discharge capacity value, a capacity retention and a capacity fade are 95 mA h g−1, 79% and 4%, respectively. Thus, it was concluded that this novel separator membrane is suitable for lithium-ion battery applications.

Homoporous polymer membrane via forced surface segregation: A computer simulation study

Forced surface segregation incorporated into non-solvent induced phase separation (NIPS) process for the preparation of the tri-block copolymer homoporous membrane was investigated by dissipative particle dynamics simulations. The copolymer bears hydrophobic cellulose acetate (CA), hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PEGMA) and low surface energy poly(hexafluorobutyl methacrylate) (PHFBM) segments. Simulation results show that the homoporous membrane can only be formed at the polymer concentration range of 15–40%. The analysis of the segment distribution of the membrane shows phase separation under different PHFBM/PEGMA block ratios. The introduction of PEGMA segments promoted the migration of low surface energy PHFBM segments to the surface of the membrane. By adjusting the mixing ratio of CA-PHFBM-PEGMA with CA from 0 to 60%, the controlled morphology regulation of the membrane can be realized. This work can serve as a guide and reference for the homoporous polymer membrane preparation via NIPS.

Bioinspired Poly(vinylidene fluoride) Membranes with Directional Release of Therapeutic Essential Oils.

Here, the morphology of polypore fungi has inspired the fabrication of poly(vinylidene fluoride) (PVDF) membranes with dual porosity by nonsolvent-induced phase separation (NIPS). The fruiting body of such microorganisms is constituted of two distinct regions, finger- and sponge-like structures, which have been successfully mimicked by controlling the coagulation bath temperature during the NIPS process. The use of water at 10 °C as coagulant resulted in membranes with the highest finger-like/sponge-like ratio (53% of the total membrane thickness), while water at 90 °C allowed the formation of macrovoid-free membranes. The microchannels and the asymmetric porosity were used to enhance the oil sorption capacity of the PVDF membranes and to achieve directional release of therapeutic essential oils. These PVDF membranes with easily tuned asymmetric channel-like porosity and controlled pore size are ideal candidates for drug delivery applications.

Microarchitecture of poly(lactic acid) membranes with an interconnected network of macropores and micropores influences cell behavior

Tissue engineering scaffolds require a three-dimensional architecture with controlled pore size and structure to host tissue formation. Here we used the non-solvent induced phase separation (NIPS) process to prepare porous asymmetric membranes made of poly(lactic acid) (PLA) using dimethylformamide (DMF) as solvent and water as non-solvent. The addition of a polymer additive to the PLA solution has made it possible to increase and control the size of open macropores at the membrane bottom surface and to generate a dual pore architecture consisting of an interconnected network of macropores and micropores. Based on the study of the compatibility of PLA with the polymer additive we propose that the dual pore architecture is generated through a two phase separations process. Membrane surface could be functionalized with hyaluronan (HA) and, whatever the cell type considered, HA-functionalization enhanced cell proliferation. Interestingly, a strong effect of macropore size and surface functionalization by HA on cell colonization and cell proliferation within membranes and membrane morphology on cell organization was demonstrated. Cancer cell lines were able to adopt an in vivo tumor-like behavior, endothelial cells reconstituted a vascular-like structure and mesenchymal stem cells adopted a specific organization which can open perspectives for their use and conservation. These results show that our membranes with controllable dual pore architecture offer great potentialities in tissue and tumor engineering.

Zwitterionic poly(arylene ether sulfone) copolymer/poly(arylene ether sulfone) blends for fouling-resistant desalination membranes

Zwitterionic polymers have drawn significant attention for membrane-based separations due to their impressive hydrophilicity and antifouling properties. Here we demonstrated a novel synthesis method to prepare an amphiphilic copolymer poly(arylene ether sulfone-co-sulfobetaine arylene ether sulfone) (PAES-co-SBAES), which was blended with native polysulfone (PSf) to prepare free standing membranes. The polymer chemical structures were analyzed by 1H NMR spectroscopy and the molecular weight of polymers was identified by size exclusion chromatography (SEC). The PSf/PAES-co-SBAES blend membranes with various zwitterionic SBAES segment contents were fabricated via the non-solvent induced phase separation (NIPS) process. The membrane composition, surface morphology (roughness), and surface hydrophilicity were determined by fourier transform infrared (FT-IR) spectrum, atomic force microscopy (AFM), and water contact angle measurements, respectively. The cross-section morphology and surface hydrophilicity of the as-made membranes was analyzed by scanning electron microscopy (SEM) and water contact angle measurements, respectively. The results indicated that both the porosity of the support layer and surface hydrophilicity increased drastically due to the incorporation of hydrophilic SBAES segments. The water permeance and antifouling ability of the PSf/PAES-co-SBAES blend membranes were both remarkably improved to 2.5 L m−2 h−1 bar−1 and 94% of flux recovery ratio, respectively, while salt rejection remained at a high level (98%) even under the high exposure to chlorine. This work provided a valuable and scalable strategy to fabricate desalination membranes via the introduction of zwitterionic segments in a rigid polysulfone matrix, and we predict that additional polymer optimization will drive the performance even higher.

Modulation of the mechanical, physical and chemical properties of polyvinylidene fluoride scaffold via non-solvent induced phase separation process for nerve tissue engineering applications

The aim of this research was to develop microporous poly(vinylidene fluoride) (PVDF) scaffolds with an intrinsic electrical property, via the combination of non-solvent induced phase separation (NIPS) and thermal induced phase separation (TIPS) process referred as N-TIPS method. For this purpose, the effects of non-solvent incorporation (distilled water) in the solvent composition (N,N-dimethylformamide (DMF)), immersion time at coagulation bath (1, 3, 6 and 24 h) as well as coagulation bath temperature (−10, 0 and 20 °C) and composition (DMF:water volume ratio = 2:6 and 6:4) on the properties of the produced scaffolds were investigated. Results confirmed that N-TIPS processing parameters had a profound effect on the morphological, mechanical, physical and thermal properties of the PVDF scaffolds. For instance, with increased bath temperature, the formation of three-dimensional bi-continuous scaffold with average pore size of 4.2 ± 0.6 μm was achieved, whereas increase in the immersion time in coagulation bath from 1 to 24 h induced cellular morphology with a larger pore size. The formation of relatively small pore size and uniform foam-like structure at 3 h soaking in coagulation bath showed to improved mechanical properties of the scaffolds. It was also found that toughness of the scaffolds significantly promoted from 27.5 ± 16.4 MPa (after 1 h soaking) to 155.2 ± 25.4 MPa (after 3 h soaking). Moreover, depending on the functional parameters of N-TIPS process, β phase fraction and crystallinity of the PVDF scaffolds were in the range of 61–87% and 30–47%, respectively. Remarkably, 3 h soaking of PVDF polymer solution in coagulation bath with composition of 6:4 (D-3h-64 scaffold) significantly enhanced the crystallinity (47.03%) and β phase fraction (87.9%) and reduced crystallite size of PVDF polymer. The PC12 cell attachment and proliferation on PVDF scaffolds prepared at various parameters were also investigated. Noticeably, D-3h-64 scaffold with enhanced crystallinity and β phase fraction and significantly higher toughness could promote cell spreading and proliferation. The results presented in this study show a great potential of PVDF scaffolds with desired properties for nerve tissue engineering application.

In situ formation of La(OH)3-poly(vinylidene fluoride) composite filtration membrane with superior phosphate removal properties

It is of great practical interest to combine membrane filtration with the removal of phosphate, which is the key nutrient in waters causing the eutrophication. In this study, we report the first example of in situ formation of La(OH)3 nanorods in poly(vinylidene fluoride) (PVDF) membrane by adding LaCl3·7H2O precursor in the membrane casting solution, after a non-solvent induced phase separation process in alkaline solution. The structures, morphologies, and surface properties of the La(OH)3-PVDF composite membranes were characterized by SEM, TEM, XRD, FT-IR, XPS, and water contact angle measurements. The adsorption and filtration experiments demonstrated that the La(OH)3-PVDF composite membrane exhibited a molecular weight cut-off of 16 kDa and superior adsorption and filtration properties, i.e. high adsorption capacity (256.6 mg P/g (La)), fast adsorption kinetics, excellent regenerability, negligible lanthanum leakage, efficient phosphate removal under high filtration permeability and simultaneous removal of organic pollutants and phosphate. We hope that our work has presented a new direction for the design of filtration membrane with superior adsorption properties.

Estimation of phase separation temperatures for polyethersulfone/solvent/non-solvent systems in RTIPS and membrane properties

Phase separation temperature estimations, based on Hansen solubility parameters for poly(ethersulfone) (PES)/solvent/non-solvent systems, were carried out to study the control of phase separation temperature in a reverse thermally induced phase separation (RTIPS) process. Four membrane-forming systems were studied, namely PES/N,N-dimethylacetamide (DMAc)/diethylene glycol (DEG), PES/DMAc/polyethylene glycol 200 (PEG200), PES/DMAc/PEG300 and PES/DMAc/PEG400. The effects of PES molecular weights, PES concentrations, PEG molecular weights and ratios of non-solvent/solvent on phase separation temperature are investigated, and the theoretical Hansen solubility parameter calculation is used to establish a prediction equation for phase separation temperature. A linear relationship between the experimental data and the difference in the solubility parameters between PES and the mixed solvent was observed. When the membrane-forming temperature was higher than the cloud point, membranes with a bi-continuous structure were acquired and showed a higher pure water permeation flux than that of membranes prepared with the non-solvent induced phase separation (NIPS) process. The pure water permeation flux and the mean pore size of membranes prepared with the RTIPS process decreased in line with an increase of PES molecular weight. When the membrane formation mechanism was the RTIPS process, the mechanical properties were better than those of the corresponding membranes prepared with the NIPS process.