Vapor-induced Phase Separation Process Research Articles

Recyclable and leakage-suppressed microcellular liquid–metal composite foams for stretchable electromagnetic shielding

The metallic conductivity and high liquidity of liquid metal (LM) make LM-polymer composites exhibit high electrical conductivity, large stretchability, and excellent mechanical–electrical decoupling, which provide significant advantages in the fabrication of stretchable electromagnetic interference (EMI) shielding materials. However, problems such as undesired LM leakage, high density, and poor recyclability due to the frequent use of chemically cross-linked polymers limit the applications of LM-polymer composites. Herein, we report the fabrication of stretchable and recyclable microcellular thermoplastic polyurethane (TPU)/LM composite foams (TLFs) with controllable LM distribution through a water–vapor-induced phase separation (WVIPS) process. The sedimentation of LM droplets helps to improve the shielding effectiveness (SE) of TLF, while the microcellular structure enables TLF with more uniform LM dispersion to achieve high leakage resistance. Moreover, the stretch-activated TLF shows high electrical stability with only slight resistance changes during stretching and exhibits a strain-insensitive shielding behavior. As a stretchable joule heater, the sample has outstanding Joule-heating performance, with stable temperature dropping only slightly under large tensile strains. More importantly, the excellent solubility of TPU, combined with a solution-based WVIPS process, allows our TLFs to be easily recycled into new products with very similar structure and performance to those before recycling, indicating the ideal recyclability of such materials.

Rapid attainment of full wettability through surface PEGylation of hydrophobic polyvinylidene fluoride membranes via spray-coating for enhanced anti-biofouling performances

This manuscript explores the development of antifouling membranes fabricated by vapor-induced phase separation (VIPS) process and their spray-coating modification with an aqueous solution of a copolymer comprising butyl methacrylate and poly(ethylene glycol) methyl ether methacrylate, designated as poly(BMA-r-PEGMA). An initial optimization phase focused on improving the modification quality, with the aim of enhancing the wettability on both the top and bottom surfaces of the membranes, despite spraying on the top surface only. Our findings reveal that a sprayed solution concentration of 10 mg/mL, a pressure of 0.25 MPa, and a scan rate of 3000 mm/min achieved a decrease in water contact angle to 0 in less than 12 s for both membrane surfaces (the top surface directly exposed to the spray, and the bottom surface facing the instrument stage), suggesting that the spray-coating modifies the entire membrane’s bulk. The presence of the copolymer on both surfaces was also evidenced by FTIR and XPS tests. Further biofouling assessments demonstrated the performances of the optimized membrane (OM). In static attachment tests, the OM exhibited a high reduction in Escherichia coli adhesion, with less than 10 % adhering bacteria, compared to unmodified membranes. During the filtration of bacteria-containing wastewater, the OM boasted a flux recovery ratio approaching 60 % (against less than 40 % for a commercial hydrophilic membrane), a rejection rate of 99.3 %, and a water permeability of 2500 LMH/bar. Moreover, the OM was stable over a 4-week period, with a resistance to E. coli attachment remaining similar to prior immersion. These findings underscore the significant potential of spray-coating to develop stable and effective antifouling microfiltration membranes for the removal of microorganisms from wastewater.

Vapor-induced phase-separation-enabled versatile direct ink writing

Versatile printing of polymers, metals, and composites always calls for simple, economic approaches. Here we present an approach to three-dimensional (3D) printing of polymeric, metallic, and composite materials at room conditions, based on the polymeric vapor-induced phase separation (VIPS) process. During VIPS 3D printing (VIPS-3DP), a dissolved polymer-based ink is deposited in an environment where nebulized non-solvent is present, inducing the low-volatility solvent to be extracted from the filament in a controllable manner due to its higher chemical affinity with the non-solvent used. The polymeric phase is hardened in situ as a result of the induced phase separation process. The low volatility of the solvent enables its reclamation after the printing process, significantly reducing its environmental footprint. We first demonstrate the use of VIPS-3DP for polymer printing, showcasing its potential in printing intricate structures. We further extend VIPS-3DP to the deposition of polymer-based metallic inks or composite powder-laden polymeric inks, which become metallic parts or composites after a thermal cycle is applied. Furthermore, spatially tunable porous structures and functionally graded parts are printed by using the printing path to set the inter-filament porosity as well as an inorganic space-holder as an intra-filament porogen.

Zwitterionic Tröger's Base Microfiltration Membrane Prepared via Vapor-Induced Phase Separation with Improved Demulsification and Antifouling Performance.

The fouling of separation membranes has consistently been a primary factor contributing to the decline in membrane performance. Enhancing the surface hydrophilicity of the membrane proves to be an effective strategy in mitigating membrane fouling in water treatment processes. Zwitterionic polymers (containing an equimolar number of homogeneously distributed anionic and cationic groups on the polymer chains) have been used extensively as one of the best antifouling materials for surface modification. The conventional application of zwitterionic compounds as surface modifiers is intricate and inefficient, adding complexity and length to the membrane preparation process, particularly on an industrial scale. To overcome these limitations, zwitterionic polymer, directly used as a main material, is an effective method. In this work, a novel zwitterionic polymer (TB)-zwitterionic Tröger's base (ZTB)-was synthesized by quaternizing Tröger's base (TB) with 1,3-propane sultone. The obtained ZTB is blended with TB to fabricate microfiltration (MF) membranes via the vapor-induced phase separation (VIPS) process, offering a strategic solution for separating emulsified oily wastewater. Atomic force microscopy (AFM), scanning electron microscopy (SEM), water contact angle, and zeta potential measurements were employed to characterize the surface of ZTB/TB blended membranes, assessing surface morphology, charge, and hydrophilic/hydrophobic properties. The impact of varying ZTB levels on membrane surface morphology, hydrophilicity, water flux, and rejection were investigated. The results showed that an increase in ZTB content improved hydrophilicity and surface roughness, consequently enhancing water permeability. Due to the attraction of water vapor, the enrichment of zwitterionic segments was enriched, and a stable hydration layer was formed on the membrane surface. The hydration layer formed by zwitterions endowed the membrane with good antifouling properties. The proposed mechanism elucidates the membrane's proficiency in demulsification and the reduction in irreversible fouling through the synergistic regulation of surface charge and hydrophilicity, facilitated by electrostatic repulsion and the formation of a hydration layer. The ZTB/TB blended membranes demonstrated superior efficiency in oil-water separation, achieving a maximum flux of 1897.63 LMH bar-1 and an oil rejection rate as high as 99% in the oil-water emulsion separation process. This study reveals the migration behavior of the zwitterionic polymer in the membrane during the VIPS process. It enhances our comprehension of the antifouling mechanism of zwitterionic membranes and provides guidance for designing novel materials for antifouling membranes.

A Ti3C2 MXene-integrated near-infrared-responsive multifunctional porous scaffold for infected bone defect repair.

Infected bone defect repair has long been a major challenge in orthopedic surgery. Apart from bacterial contamination, excessive generation of reactive oxygen species (ROS), and lack of osteogenesis ability also threaten the defect repair process. However, few strategies have been proposed to address these issues simultaneously. Herein, we designed and fabricated a near-infrared (NIR)-responsive, hierarchically porous scaffold to address these limitations in a synergetic manner. In this design, polymethyl methacrylate (PMMA) and polyethyleneimine (PEI) were used to fabricate the porous PMMA/PEI scaffolds via the anti-solvent vapor-induced phase separation (VIPS) process. Then, Ti3C2 MXenes were anchored on the scaffolds through the dopamine-assisted co-deposition process to obtain the PMMA/PEI/polydopamine (PDA)/MXene scaffolds. Under NIR laser irradiation, the scaffolds were able to kill bacteria through the direct contact-killing and synergetic photothermal effect of Ti3C2 MXenes and PDA. Moreover, MXenes and PDA also endowed the scaffolds with excellent ROS-scavenging capacity and satisfying osteogenesis ability. Our experimental results also confirmed that the PMMA/PEI/PDA/MXene scaffolds significantly promoted new bone formation in an infected mandibular defect model. We believe that our study provides new insights into the treatment of infected bone defects.

Assessment of the DCMD performances of poly(vinylidene difluoride) vapor-induced phase separation membranes with adjusted wettability via formation process parameter manipulation

Poly(vinylidene difluoride) (PVDF) membranes for direct contact membrane distillation (DCMD) are commonly modified to decrease their wettability by water. Yet, the vapor-induced phase separation (VIPS) process may be a suitable alternative to avoid complex and expensive modifications. Superhydrophobic membranes with a water contact angle >152° were prepared in one single step by adjusting the polymer concentration, dissolution temperature, relative humidity, and exposure time to vapors to 10 wt%, 40 °C, 80 % and 10 min, respectively with N-Methyl-2-pyrrolidone (NMP) as the solvent. Compared to commercial polytetrafluorethylene (PTFE) membrane, the VIPS PVDF membrane showed higher water vapor flux (38 LMH vs 36 LMH), lower flux decline ratio (22 % vs 39 %) and superior salt rejection (99.99 % vs. 99.90 %) in a 3 h-DCMD process. In wetting tests, the VIPS membrane failed for a sodium dodecyl sulfate concentration of 0.2 mM while 0.1 mM was enough to trigger wetting of the commercial membrane. The energy barrier to heterogeneous crystallization was slightly larger for the VIPS membrane, and a higher rejection was measured during scaling tests (99.8 % vs. 94.2 % for PTFE membrane). Finally, the VIPS membrane outperformed the commercial membrane in a long-term test (100 h). These results evidence the suitability of VIPS PVDF membranes for DCMD.

A Green Stable Antifouling PEGylated PVDF Membrane Prepared by Vapor-Induced Phase Separation.

While green solvents are being implemented in the fabrication of polyvinylidene fluoride (PVDF) membranes, most are not compatible with the vapor-induced phase separation (VIPS) process for which relatively low dissolution temperatures are required. Additionally, preparing antifouling green membranes in one step by blending the polymer with an antifouling material before inducing phase separation remains extremely challenging due to the solubility issues. Here, the green solvent triethyl phosphate (TEP) was used to solubilize both PVDF and a copolymer (synthesized from styrene monomer and poly(ethylene glycol) methyl ether methacrylate). VIPS was then used, yielding symmetric bi-continuous microfiltration membranes. For a 2 wt% copolymer content in the casting solution, the corresponding membrane P2 showed a homogeneous and dense surface distribution of the copolymer, resulting in a high hydration capacity (>900 mg/cm3) and effective resistance to biofouling during the adsorption tests using bovine serum albumin, Escherichia coli or whole blood, with a measured fouling reduction of 80%, 89% and 90%, respectively. Cyclic filtration tests using bacteria highlighted the competitive antifouling properties of the membranes with a flux recovery ratio after two water/bacterial solution cycles higher than 70%, a reversible flux decline ratio of about 62% and an irreversible flux decline ratio of 28%. Finally, these green antifouling membranes were shown to be stable despite several weeks of immersion in water.

Heavy metal removal using structured sorbents 3D printed from carbon nanotube-enriched polymer solutions

<h2>Summary</h2> Sorbents with structures tailored at the molecular through device scales are needed to meet the demand for separations that can isolate trace analytes from complex mixtures. Here, direct-ink-writing three-dimensional (3D) printing is combined with a surface-segregation and vapor-induced phase separation (SVIPS) process to create hierarchically structured sorbents that satisfy this criterion. Composite inks containing polysulfone, polystyrene-<i>block</i>-poly(acrylic acid) (PS-PAA), and carbon nanotubes (CNTs) were formulated to allow these processes to proceed simultaneously. Enriching the inks with CNTs modulated their rheological characteristics such that microstructured sorbents with permeabilities of ∼10⁵ L m⁻² h⁻¹ bar⁻¹ could be printed. The SVIPS process generated an interconnected network of PAA-lined nanopores whose chemistry was tailored to produce sorbents that recovered Co²⁺ selectively from mixtures of Co²⁺ and Li⁺ and efficiently treated sub-parts per million feed solutions under dynamic flow conditions. The versatile combination of 3D printing and SVIPS provides new strategies for manufacturing next-generation sorbents with structures controlled across multiple length scales.

Engineering sterilization-resistant and fouling-resistant porous membranes by the vapor-induced phase separation process using a sulfobetaine methacrylamide amphiphilic derivative

The in-situ modification of polyvinylidene fluoride (PVDF)-based membranes with zwitterionic copolymers for environmental applications remains challenging because of the large polarity difference between PVDF and zwitterionic materials. Besides, common zwitterionic units such as sulfobetaine methacrylate fail when exposed to elevated temperatures, limiting their range of applications in biomedical engineering. We designed an amphiphilic copolymer containing sulfobetaine methacrylamide (SBAA), styrene and ethylene glycol methyl ether methacrylate (EGMA) groups. Once the appropriate composition determined, membranes were prepared by vapor-induced phase separation (VIPS), a process permitting fine control over formation mechanisms, hence over the matrix structure. Sorption, mapping FT-IR and DSC tests indicated that even a low proportion of SBAA (< 10 mol%) in the P(S-r-EGMA-r-SBAA) copolymer significantly increases the proportion of non-freezable water and enhances the strength of the hydration layer, compared to a system containing styrene and EGMA groups only, P(S-r-EGMA). The modification also resulted in a large increase in membrane hydration capacity (> 550 mg/cm3 vs. < 25 mg/cm3 for the virgin membrane). Consequently, the zwitterionic copolymer could efficiently mitigate biofouling by fibrinogen (76% drop), Escherichia coli (99% decrease) or whole blood (82% reduction), even after a steam sterilization process, while the control zwitterionic sulfobetaine methacrylate material failed at maintaining its performances. Separation tests carried out with bacterial solutions revealed the ability of the zwitterionic copolymer to significantly decrease irreversible fouling (27%), compared to a commercial membrane (47%). All in all, their porous structure, hydration capacity and their ability to withstand steam sterilization make these novel porous zwitterionic membranes ideal candidates for biomedical (blood filtration) or environmental applications (water treatment).

Using the dimethyl sulfoxide green solvent for the making of antifouling PEGylated membranes by the vapor-induced phase separation process

The toxicity of common solvents used in membrane fabrication threatens the environmental sustainability and questions the claim that membrane technology is a green separation technology. Therefore, there is a need for re-orienting membrane fabrication processes towards greener solutions, making use of less toxic, and possibly environmentally friendly solvents. We employed dimethyl sulfoxide (DMSO), a non-toxic solvent, to prepare casting solutions containing polyvinylidene fluoride and an antifouling random copolymer made of polystyrene and poly(ethylene glycol) methyl ether methacrylate (PS-r-PEGMA). Membranes were formed by vapor-induced phase separation (VIPS). They were shown to be homogeneous in terms of structure and surface chemistry (tested by mapping FT-IR), suggesting compatibility of the polymer/copolymer/solvent system and justifying the choice of DMSO. Membrane hydration was drastically improved after adding PS-r-PEGMA with a water contact angle falling from 140° to 47°. As a result, biofouling by Escherichia coli and whole blood was reduced by > 90% in static conditions. During several filtration cycles of a highly fouling Escherichia coli solution flux recovery ratio could be increased from 16% (pristine membrane) to 29% (PEGylated membrane). All in all, this study reveals that low-biofouling homogeneous porous membranes can be prepared by in-situ modification and the VIPS process using a greener approach than traditionally reported.

Intelligent sterilizable self-cleaning membranes triggered by sustainable counterion-induced bacteria killing/releasing procedure

The separation efficiency of currently developed bacteria-removal membrane system will be limited and lost due to the chemical cleaning and regeneration procedure. The main innovation of this research is the development of a novel intelligent bacterial filtration process to produce a polycationic membrane separation system that continuously kills and releases bacteria even after a 121 °C sterilization procedure. This work breaks through the possibility of introducing medical-grade sterilization procedures for clinical applications while providing the implementation of self-cleaning techniques that can be facilitated by sustainable cycle operation. The polycationic membrane was prepared by the vapor-induced phase separation (VIPS) process to control the membrane formation of polyvinylidene difluoride (PVDF) blended with a new copolymer of poly(butyl methacrylate-co-(trimethylamino)propyl methacrylamide chloride) (PVDF/PBTP). The tested hypothesis is to validate the effect of the chemical-segment substitution of methacrylamide for methacrylate on the bacteria-killing/releasing functions. The reversible molecular interaction between the membrane and microorganisms is driven by controlling the electrostatic attraction adjusted by a multivalent negatively charged ions. The PVDF/PBTP membrane can sustainably provide more than 80% bacteria-killing efficiency after the high-pressure steam sterilization process. The results of multiple bacterial separation cycles show that the PVDF/PBTP membrane can exhibit a bacteria-killing level of more than 82% and an average bacteria-releasing level of 75% without aging under 5 repeated membrane filtrations. The significant results show that PVDF/PBTP membrane exhibit excellent bacteria-killing/releasing function proved through multiple cycles of bacterial isolation. The new self-cleaning membrane developed in this study can provide a potential strategy to effectively remove potentially harmful microorganisms in domestic water and industrial wastewater, and significantly reduce its environmental pollution and bacterial pathogenicity.

Poly(vinylidene fluoride) membranes with underwater superoleophobicity for highly efficient separation of oil-in-water emulsions in resisting fouling

Oil droplets can adsorb on the surface or enter the pore channels during membrane separation, causing a decrease in water flux and increasing the number of washing and replacements, thus increasing costs. So, membrane fouling seriously limits the use of the membrane in the purification of wastewater containing oils. Generally, the underwater superoleophobic surface provides better resistance to oils, which can be fabricated by the synergistic effects of the rough structure and hydrophilic groups are required. Here, poly(vinylidene fluoride)/poly(2-hydroxyethyl methacrylate) (PVDF/PHEMA) composite membranes with the continuous sponge-like rough structure were prepared by the vapor-induced phase separation process (VIPS), and then they were furthermore co-deposited by tannic acid (TA) and N-aminoethyl piperazine propane sulfonate (AEPPS). The zwitterionic surfaces with excellent underwater anti-oil adhesion ability can efficiently separate crude oil-in-water having the flux 1056 ± 102 L m−2 h−1 bar−1 and toluene-in-water emulsions having the flux of 1593 ± 163 L m−2 h−1 bar−1, the separation efficiency is more than 99%. Moreover, they exhibit excellent underwater anti-oil adhesion ability, excellent stability, and reversibility. Our work develops rough and porous surfaces with stable underwater superoleophobicity in an efficient way, which enables the resulting membranes to be used in the continuous purification of oily wastewater.

Efficient Fenton-Like Catalysis Boosting the Antifouling Performance of the Heterostructured Membranes Fabricated via Vapor-Induced Phase Separation and In Situ Mineralization.

A photocatalytic membrane with significant degradation and antifouling performance has become an important part in wastewater treatment. However, the low catalyst loading on the polymer membrane limits its performance improvement. Herein, we fabricated poly(vinylidene fluoride) (PVDF) and poly(acrylic acid) (PAA) blend membranes with a rough surface via a vapor-induced phase separation (VIPS) process. Then Fe3+ was cross-linked with the carboxyl groups on the membrane surface and further in situ mineralized into β-FeOOH nanorods. The resultant membranes exhibit not only hydrophilicity and underwater superoleophobicity but also favorable separation efficiency and high water flux in oil-in-water emulsions separation. Under visible light irradiation, the membrane can degrade methylene blue (MB) to 95.2% in 180 min. More importantly, the membrane has a significant photocatalytic self-cleaning ability for crude oil with a flux recovery ratio (FRR) as high as 94.1%. This work brings a new strategy to fabricate the rough and porous surface for high loading of the hydrophilic photo-Fenton catalyst, improving the oil/water emulsion separation and antifouling performance of the membranes.

Thermostable antifouling zwitterionic vapor-induced phase separation membranes

Biofouling resistance of membranes is generally evaluated in normal conditions of temperature. Yet, some membranes can undergo heat treatments either before use (sterilization for biomedical use) or during operation (when temperature gradient is the driving force to the separation), which can impair the anti-biofouling material. Here, we prepared zwitterionic polyvinylidene fluoride membranes by the vapor-induced phase separation (VIPS) process, using a copolymer made of styrene units and zwitterionized 4-vinylpyridine. Membranes were fully characterized by a variety of physicochemical analyses to demonstrate the formation of bi-continuous structure and the presence of the zwitterionic copolymer on the surface of the membrane. Then, anti-biofouling properties were studied at ambient temperature using Escherichia coli bacteria, whole blood, platelet rich plasma and bovine serum albumin, before moving onto their assessment at higher temperature (60 °C) or after a steam sterilization of the membranes. Results demonstrated that anti-biofouling properties were sustained despite the heat treatment, while some common zwitterionic anti-biofouling materials (sulfobetaine methacrylate) is known to fail in similar conditions. Hence, the present membranes can be applied in a large variety of domains where bi-continuous microfiltration anti-biofouling membranes are needed and undergo heat exposure or heat treatment.

Cellulose acetate membranes fabricated by a combined vapor-induced/wet phase separation method: morphology and performance evaluation

Cellulose acetate (CA) microfiltration membranes were fabricated by a combined vapor-induced and wet phase separation technique. A systematic morphology study was performed on the membranes prepared under different fabrication conditions and dope solution compositions. The results showed that symmetric CA membranes could be obtained by controlling relative humidity, temperature and exposure time during vapor-induced phase separation step. While the surface morphology and pore size of the membranes could be mainly tailored by adjusting the dope solution composition. The performance study of the membranes showed that for operation at low transmembrane pressures, only symmetric membranes fabricated by vapor-induced phase separation process have permeability which can be reached 100 L/m2h using polyvinylpyrrolidone with an average molecular weight of 30,000 (PVPK30) or polyethylene glycol with an average molecular weight of 400 (PEG400) as additives. Bacteria removal performance of the membranes showed that samples prepared at optimized solution compositions of CA/PVP and CA/PEG fabricated at constant vapor-induced phase separation (VIPS) condition of 5 min exposure time, 45 °C and 55% relative humidity can completely filtrate the E. coli bacteria. The prepared CA membranes showed no cytotoxicity in mouse L929 fibroblast cells, confirming their biocompatible nature for possible water treatment or biomedical applications.

Reducing the pathogenicity of wastewater with killer vapor-induced phase separation membranes

While smart antibacterial surfaces with bacteria-killing/bacteria-releasing properties have been reported, no strategy existed up to date to prepare phase-inversion membranes having these capabilities in one single step, without any surface-modification. We addressed this challenge by synthesizing two copolymers made of butyl methacrylate (BMA) units and of 2-(dimethylamino)ethyl methacrylate (DMAEMA), poly(BMA-r-DMAEMA), or (trimethylamino)ethyl methacrylate chloride (TMAEMA), poly(BMA-r-TMAEMA), both miscible with poly(vinylidene fluoride) (PVDF), and prepared membranes by the vapor-induced phase separation process. Results showed that all membranes were able to kill almost 100% of bacteria that came into contact with the surface. A washing procedure with a saline solution of sodium hexametaphosphate permitted to regenerate the membrane modified with poly(BMA-r-TMAEMA). Strong hydration of the interface between positively-charged brushes and dead bacteria after docking with hexametaphosphate anions, combined to the excess of negative charges, results in bacteria release following conformational changes of poly(BMA-r-TMAEMA) polyelectrolyte brushes. However, the membrane modified with poly(BMA-r-DMAEMA) could not be regenerated, likely because poly(BMA-r-DMAEMA) does not behave as a polyelectrolyte. Results also reveal that poly(BMA-r-TMAEMA)-modified PVDF membranes were able to kill various species of bacteria, and that multiple cycles could be successively run. The prepared MF membranes are able to kill the majority of microorganisms once they contact the membrane during filtration. Domains of applications are numerous from wastewater-treatment to healthcare applications, wherever bacteria are wanted dead after separation.

Fine-tuning of the surface porosity of micropatterned polyethersulfone membranes prepared by phase separation micromolding

Phase separation micromolding (PSμM) is an effective technique for fabricating porous membranes with micropatterned structures. However, reports on procedures to control the size and number of open pores on the patterned surface are scarce, which often limits the use of the surface-patterned membranes. This work presents a systematic study on tailoring open pores on the patterned surface of polyethersulfone (PES) membranes prepared by the PSμM procedure. The composition of the solvent and the concentration of PES in the casting solution were optimized to tune the size and number of pores on the membrane surfaces formed on a flat substrate during the nonsolvent-induced phase separation (NIPS) process. The surface porosity changed significantly and macrovoids appeared when the flat substrate was replaced by a micropatterned substrate. The vapor-induced phase separation process was applied prior to the NIPS process to prevent the formation of macrovoids. The composition of the casting solution was tuned again to prepare micropatterned porous PES membranes with open pores on the patterned surface. We observed that the size and number of pores were different depending on the pore locations on the patterned surface, which was caused by different solvent/nonsolvent demixing dynamics resulting from the physical discontinuity of micro-patterned membranes. This work presents a method on tailoring open pores on the patterned surface of polyethersulfone membrane prepared by the phase separation micromolding. By modifying both the thermodynamics of the casting solution and the dynamics of solvent/nonsolvent demixing, micropatterned membrane with average surface open pores in the diameter of 1095 nm and porosity as high as 31.4% was achieved. The size and number of pores were different depending on their locations on the patterned surface, which was caused by different solvent/nonsolvent demixing dynamics resulting from the physical discontinuity of micro-patterned membranes.

PH-responsive poly(vinylidene fluoride)/poly(acrylic acid) porous membranes prepared via an vapor induced phase separation technique for removing copper ions from water

Here, polyvinylidene fluoride/poly (acrylic acid) (PVDF/PAA) membranes were fabricated via vapor-induced phase separation (VIPS) process for the first time. The casting solution was synthesized via in situ cross-linking polymerization of AA in PVDF solution and spread into glass plate. After holding in water vapor for a determined exposure time, they were soaked in the water bath. With the increase of exposure time, the membrane surface changed from dense morphology to petal-like structure, and the concentration of carboxyl groups on the membrane increased. The fabricated membranes exhibited strong pH-dependent permeability and high adsorbing capacity of Cu2+ ions from water.

Water vapor induced phase separation: a simple and efficient method for fabricating polyetherimide microspheres

In this paper, a simple and efficient method coupled with water vapor induced phase separation (WVIPS) technique has been successfully applied for the fabrication of Polyetherimide (PEI) microsphere, exhibiting well spherical shape with a relatively uniform size. The formation mechanism of water vapor induced phase separation process is discussed in detail. Furthermore, the effects of the PEI solution concentration, preparation temperature and relative humidity (RH) on the structure and size of PEI samples were investigated. Lower PEI solution concentration is much more favorable to fabricate PEI microspheres. The SEM images and the particle size analysis show that adjusting the preparation temperature and relative humidity during the fabrication process can control the average size of PEI microspheres, ranging from 725 nm to 1.9 μm based on the 3 wt% PEI solution system. This WVIPS method is simple and efficient, and could broaden the applications area of PEI composite materials.

Tuning the molecular design of random copolymers for enhancing the biofouling mitigation of membrane materials

Although a lot has been done on the making of antifouling membranes using PEGylated materials, numerous molecular design improvements can still be made on fine-tuning of both composition and chain length. Here, an antifouling copolymer made of styrene and ethylene glycol methacrylate units (PS-co-PEGMA) was used and the results demonstrate that by altering the molar ratio and chain length PS/PEGMA, it can turn the membrane from low-biofouling to almost entirely fouling resistant. At first, a set of 7 copolymers with a molecular weight in a same range but different compositions was prepared, characterized and was used to modify poly(vinylidene fluoride) (PVDF) membranes by vapor-induced phase separation (VIPS) process. Membranes were fully characterized, and antifouling tests carried out with Escherichia coli, Stenotrophomonas maltophilia and fibrinogen all showed that a 30 mol% polystyrene content in the copolymer (PS30P70) led to the best antifouling properties. Increasing or decreasing the styrene amount resulted in increasing the hydrophobicity of the material or decreasing the stability of the modification, respectively, which outcome in both cases was a higher biofouling. Then, 5 copolymers with a fixed composition but different Mws were prepared, and antifouling tests indicated that the longer the chain, the better the antifouling properties. The chain length is essential to the strength of the hydration layer as supported by both mapping FT-IR and DSC measurements.