Non-solvent Phase Separation Research Articles

A new anti-biofouling microfiltration: Combining sharkskin-inspired topology with in-situ silver nanoparticles

Recently, significant research has been undertaken to address drinking and wastewater treatment, food and beverage manufacturing, and the pharmaceutical industry in a sustainable and advanced manner. Contemporary microfiltration systems demonstrate notable efficacy in achieving high-precision separation for the products of these processes; however, they are profoundly susceptible to biofouling, which involves the accumulation of proteins and microorganisms, ultimately leading to a deterioration in separation performance. Here, we introduce the fabrication of a multifunctional anti-biofouling microfiltration membrane comprising a high-fidelity sharkskin-inspired pattern, anti-adhesive, and biocidal surface. Additionally, passive (e.g., pattern and negatively charged surface) and active (e.g., Ag nanoparticle) anti-biofouling features are spontaneously introduced through non-solvent induced phase separation and consecutive mild alkali treatment. The resulting membrane demonstrates a 188 % reduction in the accumulation of bovine serum albumin and exhibits a long-lasting biocidal effect without compromising separation performance.

Direct observation on the phase separation of polymer membrane embryos confined by microfluidics chips

In this paper, the growth of finger-like droplets inside various polymer membrane embryos induced by non-solvent phase separation (NIPS) is studied in details by using a standardized optical microscopic observation method. The boundary conditions of the phase separation are well-defined by microfluidics technology. The growth of finger-like droplets and Marangoni convection inside them are tracked and recorded by high-speed camera of sharp resolutions. Effects of the geometry of the membrane embryos (thickness/shape/size), humidity of the atmosphere and the viscosity of the embryos on the growth of finger-like droplets are systematically studied. Except the qualitative observations that are consistent to previous relative reports, more quantitative data are provided in this paper. The diffusing speed of the interface of the developing large droplets is measured by template matching algorithm. Strikingly, the time-dependent diffusing speed of the developing large droplets shows a wave-like declining pattern, which indicates that fluctuating boundary conditions are surrounding the membrane embryos. The Reynolds number of the flow inside the developing large droplets is estimated at the order of 10−5, the magnitude of which is 2 order smaller than that of a swimming sperm.

Harnessing the power of hollow Zein nanoparticles for enhanced antifouling and heavy metal removal of polyethersulfone membranes

This study explores the physicochemical characteristics of an innovative mixed matrix membrane made from polyethersulfone (PES) and hollow Zein nanoparticles (HZNs), which are derived from the corn storage protein, Zein. HZNs, with a mean diameter of 40 nm, were applied to address the challenges associated with metal and inorganic nanoparticles, such as their tendency to accumulate unevenly on the membrane surface. The membranes were fabricated by incorporating varying concentrations of HZNs into the PES casting solution through the nonsolvent phase separation method. The addition of HZNs enhanced the hydrophilicity and pure water flux of the membranes. It also modified the membrane structure, morphology, pore size, molecular weight cut-off (MWCO), and porosity. Increasing the HZN concentration up to 5 wt% proportionally improved the surface hydrophilicity and roughness of the membranes. Furthermore, the modified membranes exhibited excellent performance in rejecting heavy metals at an acidic pH of 4, with the 5 %-HZNs/PES membrane achieving a 100 % rejection rate without significantly affecting water flux due to Donnan exclusion. Additionally, the 5 %-HZNs/PES membrane showed a minimal irreversible fouling resistance (Rir) of 17.9 % and a fouling resistance ratio (FRR) of 82.1 %. These results indicate that the developed mixed matrix membrane holds significant promise for applications in water purification processes.

Preparation of novel zwitterionic polysulfone ultrafiltration membranes for the dual-enhanced antifouling and antibacterial properties by in-situ one pot crosslinking reaction

Zwitterionic polysulfone (PSf) ultrafiltration membranes were fabricated by non-solvent phase separation (NIPS) method. Herein, a casting solution at 45 °C was developed by using chloromethylated polysulfone (CMPSf), N, N-dimethylacetamide (DMAc) as a solvent, 4-amino-benzenesulfonic acid monosodium salt (ABS) as a cross-linking agent, and Na2CO3 as an acid binder. Simultaneously, the occurrence of the electrophilic substitution reaction between ABS and CMPSf caused the formation of ABS grafting CMPSf (CMPSf-g-ABS). After a specific reaction time, the casting solution was applied to cast membranes, which were subsequently submerged in coagulation bath. A zwitterionic ultrafiltration (ZUF) membrane was obtained using NIPS following the treatment of hydrochloric acid (HCl) solution (1 M mol). Because of the formation of cross-linked CMPSf-g-ABS, the results revealed that the casting solution's viscosity increased sharply from 425.4 mPa s at the initial stage (0 h) to 4810.8 mPa s (22 h). Interestingly, the morphology of the membranes with an asymmetric finger-like structure at 0 h gradually transformed to a gradient sponge-like structure after 22 h. Specifically, the ZUF membrane (M22-H) with the gel fraction of 72.1% procured after the reaction of 22 h demonstrated a low water contact angle (40.17°) and a high pure water permeance (420.4 L m−2 h−1 bar−1). The M22-H also exhibited a high flux recovery rate (FRR) (90.2%), bovine serum albumin (BSA) rejection (>95%), and Escherichia coli (E. coli) antibacterial rate (96.2%). The surface of the ZUF membrane with numerous zwitterionic groups enhances the hydration layer's energy (i region <16 nm) and creates a thick hydration layer (ii region >16 nm), causing a significant improvement in the antifouling performance. This research opens new avenues for preparing zwitterionic functional membranes.

In-situ polarized coaxial PVDF/PL nanofiber filtration membrane with high efficiency, low resistance and antimicrobial properties

Aerosols are prone to breed bacteria on air filtration materials so as to cause secondary air pollution, especially carrying bacteria and viruses. This paper utilized coaxial electrospinning technology with traditional Chinese medicine Physalis alkekengi Linn as the core layer antibacterial material and polyvinylidene fluoride/polyacrylonitrile mixed solution as the shell layer material. Nonsolvent phase separation technology was employed to prepare the porous shell layer, achieving sustained slow-release and long-lasting antibacterial effects from the core P. alkekengi Linn. In addition, an in-situ polarization technology from high voltage in electrospinning process was adopted to achieve permanent polarization of polyvinylidene fluoride, which changed from α-crystal to β-crystal. Using the electrostatic charge adsorption effect and the ultra-fine pore size screening of the nanofiber membrane, high-efficiency and low-resistance filtration of aerosols above 0.3 μm was achieved (99.98% filtration efficiency and filtration resistance less than 25 Pa). It can be widely used in the field of air filtration and protection in high-risk environments such as stations, schools, and hospitals, achieving long-lasting antibacterial, high-efficiency, and low-resistance air filtration and protection.

PHASE SEPARATION AND PARTICULATE LEACHING INTEGRATED 3D PRINTING OF POROUS SCAFFOLDS FOR BONE TISSUE ENGINEERING APPLICATIONS

Conventional 3D printing by itself is incapable of creating pores on a micro scale within deposited filaments throughout 3D scaffolds. These pores and hence larger surface areas are needed for cells to be adhered, proliferated, and differentiated. The aim of this work was to fabricate 3D polycaprolactone (PCL) scaffolds with internal multiscale porosity by using two different 3D printing techniques (ink/pellet of polymer-salt composite in low/high temperature printing) combined with salt leaching to improve cell adhesion, and cell proliferation besides to change degradation rate of PCL scaffolds:1. Non-solvent phase separation integrated 3D printing of polymer-salt inks with various salt content (i.e., low temperature ink-based printing, LT).2. FDM printing of composite polymer-salt pellets which will be obtained by casting and evaporating of prepared ink (i.e., high temperature composite-pellet-based printing, HT).Further, the two approaches were followed by post salt leaching. Stem cells were able to attach on the surface and grow up to 14 days based on increasing cellular activities.

Polyimide solution with reversible sol-gel transition by construction of dynamic π-π stacking

Constructing fully rigid chain polyimides with reversible sol-gel/gel-sol transition is significant for developing high-performance and functional materials. π-π stacking, a typical weak interaction, has attracted great interest in producing functional gels, but less has been reported in polyimide organogels. This work developed new polyimide organogels using π-π interactions by incorporating bisbenzoxazole moieties with fully coplanar structures in polyimides. The reversible sol-gel transition behavior with temperature and strain response was systematically studied using rheological methods. DFT simulations, temperature-dependent NMR, UV–Vis, and fluorescence spectroscopy results confirmed the existence of the dynamic π-π interactions in polyimides. Based on the success, we further combined sol-gel methods and non-solvent phase separation methods to prepare a new type of nanofiltration (NF) membranes. The resulting NF membranes showed a higher rejection of methylene blue (rejections of 99.6%) and a good permeability of sodium salt (rejections of 5.1–7.7%), showing great promise for selective filtration of industrial dye wastewater.

Free-standing graphene/polyetherimide/ZrO2 porous interlayer to enhance lithium-ion transport and polysulfide interception for lithium-sulfur batteries

Attributing to high theoretical specific capacity and energy density, lithium-sulfur batteries (LSBs) are receiving great attention. However, the commercialization of such technology is seriously hindered by the shuttle effect of polysulfides during the round-trip charge and discharge process. Herein, with three types of carbon materials and ZrO2 nanoparticles filled in polyetherimide (PEI) support framework with good stability, porous composite films were obtained by a simple non-solvent phase separation (NIPS) as free-standing interlayers for LSBs. The obtained interlayers can not only provide hierarchical channels for improving lithium-ion transfer number, but also own excellent physicochemical stability and strong adsorption capability towards lithium polysulfide (LiPS). Compared with the pristine one, the representative LSB with graphene/polyetherimide/ZrO2 interlayer (GPZ) shows good initial cycle discharge specific capacity (1280 mAh g−1), better capacity retention (749 mAh g−1 after 200 cycles) and good rate performance (580 mAh g−1 at 2C). This work provides a facile and promising way to achieve functional interlayer with high stability for high performance LSBs.

Preparation of flexible and ultralow dielectric polyimide porous films by a low-cost and environmentally friendly non-solvent phase separation

Polyimide (PI) porous films were prepared by non-solvent induced phase separation with low-cost and simple method. A low-cost and environmentally friendly solution of water and ethanol was selected as non-solvent coagulation bath and effects of water and ethanol content on microstructure and properties was studied. The prepared films showed high mechanical property at high temperature, excellent dielectric property and thermal stability. Thus there are excellent application prospects in fields of flexible electronics and microelectronics industry.

Design and Preparation of Porous Meta-Aramid Fibers Filled with Highly Exposed Activated Carbon for Chemical Hazard Protection Fabrics

Chemical hazard protection safety and wear comfort of chemical protective clothing (CPC) are vital for the chemical personnel involved. Unfortunately, low air permeability and poor durability of adsorbate loading from conventional protective textiles coated with porous substances still cause tremendous threats to health and reduce working efficiency. Herein, to solve these limitations, highly exposed activated carbon (AC) nanoparticles are locked inside the chamber of porous meta-aramid fibers (PMIAs) from physical blending and wet-spinning as well. By controlling the pore parameters of PMIA fibers via adjusting the coagulation conditions (bath temperatures and bath composition) during the nonsolvent phase separation (NIPS) process, not only the inner AC is exposed highly but also the adsorption capability of AC-filled meta-aramid fibers to hazardous gases and corresponding mechanical properties is optimized. The resultant fiber (with 20 wt % AC) demonstrates a high adsorption capacity for benzene (102.26 mg/g), sufficient tensile strength (1.82 cN/dtex), and is recyclable. Finally, the further developed fabric from this composite fiber also offers a higher air permeability (11.4 cm3 s–1 cm–2) and a firmer loading of AC compared to commercial CPC (FFF02). This work should serve as a source of inspiration for improving the comfort and safety of CPC.

Designing polyimide/polyacrylonitrile/polyimide sandwich composite separator for rechargeable lithium-ion batteries

The thermal stability of lithium-ion battery separator is very desirable to satisfy the requirements of EVs. Polyacrylonitrile (PAN) fiber membranes with excellent ionic conductivity and polyimide (PI) with excellent mechanical properties and flame retardancy have been attracted much attention. In this study, a PI/PAN/PI sandwich separator with three-dimensional network and sponge-like structures is prepared via electrostatic spinning, non-solvent phase separation and pressed lamination method. Compared with the cells with the typical PP separators, original PAN and PI separators, the cells assembled with the PI/PAN/PI sandwich separators presented an optimum rating and cycling capability, higher discharge capacity and lower internal resistance. The maximum discharge capacity of PI/PAN/PI separator was obtained 151.56 mAh g−1 at 0.1C, and the capacity retention could be maintained 94.3 % at 1C after 100 cycles during the charge and discharge process. Besides, the PI/PAN/PI separator exhibits excellent mechanical properties (18.12 MPa) and flame retardant performance. These results indicate that this process of PI/PAN/PI sandwich separator can be an efficient and applicable approach for preparing high performance separators, which will lead to stable cyclability and superior C-rate capacity.

Facile fabrication of highly porous nylon-11 layer for flexible high-performance triboelectric nanogenerator

Here, we report a facile method for the fabrication of flexible triboelectric nanogenerator (TENG) with a porous electropositive triboelectric (TE) layer. The electropositive TE layer composed of a highly porous nylon-11 layer on a conductive fabric is first fabricated by the one-pot method of non-solvent phase separation and then assembled with the electronegative TE layer composed of poly-(vinylidene difluoride) (PVDF) nanofibers to obtain the TENG. The TENG is flexible owing to the incorporation of the porous nylon-11 layer and the PVDF nanofibers. Meanwhile, the TENG exhibits outstanding characteristics, including an output open-voltage of 323 V and a power density of 1.06 W/m2, better than those previously reported values in TENGs with nylon-11 TE layers. To demonstrate its power supply capability, the TENG is further used to power practical electronic devices. Our results provide a facile and low-cost approach for the production of a flexible TENG with high performance.

One-Step Fabrication of Porous Membrane-Based Scaffolds by Air-Water Interfacial Phase Separation: Opportunities for Engineered Tissues.

Common methods for fabricating membrane-based scaffolds for tissue engineering with (hydrophobic) polymers include thermal or liquid-phase inversion, sintering, particle leaching, electrospinning and stereolithography. However, these methods have limitations, such as low resolution and pore interconnectivity and may often require the application of high temperatures and/or toxic porogens, additives or solvents. In this work, we aim to overcome some of these limitations and propose a one-step method to produce large porous membrane-based scaffolds formed by air-water interfacial phase separation using water as a pore-forming agent and casting substrate. Here, we provide proof of concept using poly (trimethylene carbonate), a flexible and biocompatible hydrophobic polymer. Membrane-based scaffolds were prepared by dropwise addition of the polymer solution to water. Upon contact, rapid solvent–non-solvent phase separation took place on the air-water interface, after which the scaffold was cured by UV irradiation. We can tune and control the morphology of these scaffolds, including pore size and porosity, by changing various parameters, including polymer concentration, solvent type and temperature. Importantly, human hepatic stellate cells cultured on these membrane-based scaffolds remained viable and showed no signs of pro-inflammatory stress. These results indicate that the proposed air-water interfacial phase separation represents a versatile method for creating porous membrane-based scaffolds for tissue engineering applications.

Modification of Thin Film Composite Pressure Retarded Osmosis Membrane by Polyethylene Glycol with Different Molecular Weights.

An investigation of the effect of the molecular weight of polyethylene glycol (PEG) on thin-film composite (TFC) flat sheet polysulfone membrane performance was conducted systematically, for application in forward osmosis (FO) and pressure retarded osmosis (PRO). The TFC flat sheet PSf-modified membranes were prepared via a non-solvent phase-separation technique by introducing PEGs of different molecular weights into the dope solution. The TFC flat sheet PSf-PEG membranes were characterized by SEM, FTIR and AFM. The PSf membrane modified with PEG 600 was found to have the optimum composition. Under FO mode, this modified membrane had a water permeability of 12.30 Lm−2h−1 and a power density of 2.22 Wm−2, under a pressure of 8 bar in PRO mode, using 1 M NaCl and deionized water as the draw and feed solutions, respectively. The high water permeability and good mechanical stability of the modified TFC flat sheet PSF-PEG membrane in this study suggests that this membrane has great potential in future osmotically powered generation systems.

Development of floating 3D-microfloral CuO-polysulfone beads for wastewater treatment

Sustainable recycling of earth-abundant transition metals and water-overwhelming macroplastics are currently needed to alleviate depletion of resources and risks posed against environmental sustainability and health. In this contribution, copper metal recovered from an electronic waste was used to fabricate microfloral copper(II)oxide (CuO) particles via an anodized metastable pathway. Interaction of the latter with hot polysulfone in dimethylsulfoxide (DMSO) led to the formation of a floating photocatalyst via a non-solvent phase separation. The catalyst was used for the degradation of humic acid and flavonoid dyes in the presence or absence of hydrogen peroxide (H2O2), a light-emitting diode (LED) and sunlight. A pyramidal triangular model was used to predict the life cycle of H2O2 while an enhanced photocatalytic property was observed after irradiation with light. The as-synthesized materials showed attractiveness for the degradation of phenolic and carboxylic acid-bearing organic pollutants in water.

Effects of GO-PEG on the performance and structure of PVC ultrafiltration membranes

In this work, neat and nanocomposite polyvinyl chloride (PVC) membranes with various contents of graphene oxide-poly ethylene glycol (GO-PEG) nanosheets were fabricated via non-solvent phase separation (NIPS) method. The results of field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses approved the successful synthesis of GO-PEG nanosheets. Fabricated PVC/GO-PEG membranes were characterized by atomic force microscopy (AFM), water content, FESEM, contact angle, porosity, pure water flux (PWF), abrasion resistance and tensile strength tests. FESEM images illustrated the increased porosity of membranes after embedding of GO-PEG. The results showed that by addition of nanosheets, abrasion resistance of membranes enhanced as a reason of good mechanical properties of GO. Moreover, PWF was improved from 50 L/m2 h in neat PVC to around 211 L/m2 h in 0.15 wt.% PVC/GO-PEG membrane. Finally, MBR filtration test was utilized for 360 min to evaluate membranesʼ performance. In this case, Reversible Fouling Ratio (RFR) increased (from 9% in neat PVC membrane to 33% in PVC/GO-PEG 0.15 wt.% membrane) and Irreversible Fouling Ratio (IFR) decreased (from 51% in neat PVC to 37% in PVC/GO-PEG 0.15 wt.% membrane) by addition of GO-PEG nanosheets. The improved antifouling properties of PVC/GO-PEG membranes can be attributed not only to the hydrophilicity effect of GO-PEG nanosheets which prevents the foulants from attaching to membranes surface but also to the increased flux of PVC/GO-PEG membranes.

Fabrication of aramid-coated asymmetric PVDF membranes towards acidic and alkaline solutions concentration via direct contact membrane distillation

An asymmetric membrane for direct contact membrane distillation (DCMD) was first prepared with the ability to concentrate strongly acidic and alkaline solutions. The membrane was fabricated by a simple coating and non-solvent phase separation process. The successful preparation of the aramid-coated polyvinylidene fluoride (PVDF) asymmetric membrane was demonstrated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) characterization. Furthermore, it was verified via contact angle measurements that this modified membrane had better acid and alkali resistance than the pristine PVDF membrane at an elevated temperature. During the DCMD process, the pH of the permeate side did not fluctuate significantly when solutions with different pH values were used as the feed solutions, thus also demonstrating the excellent separation efficiency of the modified PVDF membrane. Moreover, the modified PVDF membrane exhibited a higher concentration factor for acidic and alkaline solutions than the pristine membrane. Therefore, it is believed that the modified membrane has great potential for application in DCMD process with the concentration of acidic and alkaline solutions.

Fabrication of asymmetric cellulose acetate/pluronic F-127 forward osmosis membrane: minimization of internal concentration polarization via control thickness and porosity

The core of this study was fabrication of novel cellulose acetate/pluronic F-127 (CA/PF-127) composite membranes for forward osmosis (FO) applications. Performance and structure of the FO membranes under the influence of different applicator clearance gaps (ACGs) along with PF-127 wt.% contents were examined during the non-solvent phase separation (NIPS) method. Scanning electron microscopy, water contact angle, atomic force microscopy and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis were used to characterize the membrane properties. The best performance was attributed to the lower thickness and the higher porosity. The lower structural parameter, which reduces the internal concentration polarization (ICP), led to the highest water flux. The values of 10.58 (L/m2.h) and 0.39 (g/L) were obtained as water flux and specific reverse salt flux (SRSF) of the optimal FO membrane, which was synthesized by 20 wt.% of CA, 79.00 wt.% of N-methyl-2-pyrrolidone (NMP), 1.0 wt.% of PF-127 and 100 µm of ACG, respectively.

The rapid and controllable fabrication of large-scale and highly ordered micro-honeycomb arrays induced by nonsolvent phase separation.

Structures that are highly ordered in nature show unique light propagation abilities. Among them, micro-honeycomb arrays are attractive owing to their advantages relating to the collection of light or enlarging the viewing angle and, also, owing to their potential applications in precision optics. Inspired by the natural phenomenon of droplet condensation on a cold surface, breath figure self-assembly has been a common approach used to fabricate such ordered micro-honeycomb arrays. However, the harsh preparation conditions and specific polymer architecture required have limited the widespread application of this approach. In this work, by using a commercial linear homopolymer and introducing its nonsolvent, we successfully fabricated uniform micro-honeycomb arrays on a large scale in just seconds and at ambient humidity. The morphology of the structures can be easily tuned via controlling the preparation conditions. Furthermore, high fill-factor convex micro-lenses were prepared based on the as-prepared concave micro-honeycomb arrays as templates through a simple replication process. They demonstrate properties such as clear multiple image presentation and light diffraction. They can also assist the strong scattering of light, which enhances the fluorescent intensity by more than 10%. This method is envisaged as a potential candidate to replace breath figure self-assembly for micro-honeycomb arrays in a low-cost and high-efficiency manner under mild conditions.

Polyurethane-modified graphene oxide composite bilayer wound dressing with long-lasting antibacterial effect

In order to obtain a novel multifunctional wound dressing with good water vapor permeability and long-lasting antibacterial properties, a skin-like thermoplastic polyurethane (TPU) bilayer membrane containing self-made polyhexamethylene guanidine hydrochloride (PHMG) grafted graphene oxide (MGO) was prepared by non-solvent phase separation and particle filtration. The antibacterial properties and wound-healing ability of TPU, GO-TPU, MGO-TPU composite porous membrane are systematically compared. The results show that with the incorporation of MGO, the porous MGO-TPU membrane exhibits good biocompatibility, excellent water vapor transmission properties, and long-lasting broad-spectrum antibacterial properties (the antibacterial property remains unchanged for 30days under continuously shaking and washing). The wound healing results for mouse model show that MGO-TPU could significantly accelerate the healing rate of wounds as it provides a sterile environment and also promotes the formation of re-epithelialization during wound healing.