Vapor-induced Phase Separation Research Articles

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.

Superhydrophobic and Low‐k Polyimide Film with Porous Interior Structure and Hierarchical Surface Morphology

AbstractPorous interior structured polyimide (PI) films with a hierarchical surface are fabricated from 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 4,4′‐oxydianiline by a water vapor induced phase separation process under a humid environment. Superhydrophobic properties with a water contact angle of 161° are obtained using the hierarchical surface morphology, which can be adjusted from flower‐like to wrinkle‐shape particles facilely by changing the relative humidity. The dielectric constant (k) of the PI film decreases sharply from 2.8 (film prepared under dry conditions) to ≈1.9 (film prepared under humid conditions) because of the interior porous structure and fluorine‐containing framework. Both a low‐k and superhydrophobicity are very important parameters for PI films in microelectronic and insulating applications.

Microfluidic preparation of polymer-lipid Janus microparticles with staged drug release property

This work demonstrated a microfluidic preparation process for novel Janus microparticles with individual drug release properties in each compartment. A flow-focusing microfluidic chip was designed to produce oil-in-water droplets from a mixed solution of poly(lactic-co-glycolic acid) and a triglyceride type lipid. Based on solvent evaporation-induced phase separation, droplets evolved and were solidified into Janus particles, each of which had a polymer compartment and a lipid compartment. The ratio of the two compartments in a particle can be discretionarily regulated, and the particle structure can also be flexibly altered to Janus-patchy, triple, quadruple or core-shell type. Phase transition of the chosen lipid from solid to liquid would occur under physiological temperature, which was applied for rapid release of the loaded drug. The polymer compartment would undergo a slow degradation process in physiological environment, facilitating sustained drug release. Paclitaxel was loaded into Janus particles during preparation, and staged release was achieved, leading to a combination of rapid and sustained release, which is highly desired in target drug delivery. This study would start the application of hybrid Janus particles of polymer-lipid type with novel release kinetics in drug delivery systems.

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACTIn this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.

Biophotonic Films: Biomimetic Polymer Film with Brilliant Brightness Using a One‐Step Water Vapor–Induced Phase Separation Method (Adv. Funct. Mater. 23/2019)

Biophotonic Films: Biomimetic Polymer Film with Brilliant Brightness Using a One‐Step Water Vapor–Induced Phase Separation Method (Adv. Funct. Mater. 23/2019)

Unprecedented preparation of porous Matrimid® 5218 membranes

In this work, for the first time, porous Matrimid® 5218 membranes were prepared by employing a combination of vapour induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) technique. N-methyl-2-pyrrolidone (NMP) and Rhodiasolv® Polarclean were used as a traditional and new green solvent, respectively, for the preparation of the membranes. Ternary phase diagrams with both solvents were preliminary carried out. The exposure time to humidity and the effect of polymer concentration on membrane morphology and properties were evaluated. The resulting membranes were fully characterized in terms of morphology, shrinkage propensity, thickness, porosity, mechanical properties, pore size, contact angle and water permeability.

Effects of hydrophilicity of blended submicrogels on the microstructure and performance of thermo-responsive membranes

The hydrophilicity of smart additives thermodynamically and kinetically affects the degree and velocity of the phase separation of casting solution, together with their distribution on the membranes, which ultimately affects the microstructure and properties of smart membrane. However, the reasonable design and successful preparation of additives with different hydrophilicity, as well as the observation of their migration during membrane formation process and final distribution on/in the membranes remain challenges. The three kinds of thermo-responsive submicrogels with similar chemical structures and different hydrophilicity were successfully fabricated and blended into poly(ether sulfone) (PES) as functional gates to prepare smart membranes via vapor-induced phase separation (VIPS). The hydrophilicity of poly(N-n-propylacrylamide) (PNN), poly(N-isopropylacrylamide) (PNI) and poly(N-isopropylmethacrylamide) (PNM) submicrogels were quantitively measured; their diameters and thermo-responsive factors in water were similar. Moreover, the effects of the hydrophilicity of submicrogels on the microstructures and properties of as-prepared smart membranes were systematically investigated and the results were elucidated in principle. The results showed the velocity of phase separation of casting solution, the pore size of membranes and the number of submicrogels distributed on membranes increased whereas the stability of submicrogels on membranes decreased with the enhancement of hydrophilicity of submicrogels. The membrane blended with PNI submicrogels with optimal hydrophilicity, which was provided with both a large number of submicrogels stably distributed on the membrane pores as smart gates and appropriate pore size, exhibited excellent permeability and thermo-responsiveness. The maximum water flux through this membrane was 26271 kg m−2 h−1 bar−1, and its maximum normalized thermo-responsive coefficient N value reached to 28.7. The results will provide valuable guidance for understanding the mechanism of phase separation and further development of smart membranes with satisfactory performances.

Microcellular polyetherimide/carbon nanotube composite foam: Structure, property and highly reinforcing mechanism

Microcellular polyetherimide (PEI)/carbon nanotube (CNT) composite foams were prepared via water vapor-induced phase separation (WVIPS) process. The hydroxylated multi-wall nanotubes (MWNTs-OH) were applied, and strong interfacial interaction formed with PEI molecules by high grafting ratio. Much PEI resin adhered to MWNTs-OH surface, resulting in an obvious increase of MWNTs-OH diameter and formation of coating structure. For the composite foams, the homogenous spherical-like cell structure can be observed. With increasing MWNTs-OH content, the tensile strength of the composite foam first increased, and then decreased, reaching maximum at 4 wt% MWNTs-OH, a roughly 53% increase as a result of reinforcing effect of MWNTs-OH on matrix. Meanwhile, the storage modulus of the composite foam was much higher than that of pure PEI foam over the temperature range tested and still maintained above 610 MPa at 200 °C, suggesting a remarkable improvement of thermal mechanical stability. MWNTs-OH distributed uniformly in the matrix, and under stress it was pulled out with surface completely wrapped by PEI resin, confirming that the failure mode was the deformation and destruction of non-interface resin. By incorporation of MWNTs-OH, the thermal decomposition temperature, char yield and LOI values of the composite foam increased, while the UL-94 tests were classed as a V-0 rating.

Adjusting the morphology of poly(vinylidene fluoride-co-hexafluoropropylene) membranes by the VIPS process for efficient oil-rich emulsion separation

Given its excellent bulk properties and highly hydrophobic nature, poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-co-HFP), is a candidate material for the gravity-driven separation of water and oil from oil-rich emulsions. For this, highly porous membranes with a controlled large pore size are necessary. An ideal process to design such structures is the vapor-induced phase separation (VIPS) process but it has been underexplored using P(VDF-co-HFP). Here, we address this challenge by presenting and discussing the formulation/process conditions that permit to obtain the desired P(VDF-co-HFP) porous bi-continuous structure by VIPS process only. Then, the membrane is fully characterized before being applied to the separation of water-in-oil emulsions, from versatile oil-rich phases, with or without the use of surfactants, in both dead-end gravity driven process and cross-flow process. In each situation, high flux and separation efficiencies were obtained, and the membrane outperformed commercial hydrophobic poly(vinylidene fluoride) (PVDF) membranes of similar pore size/porosity in every aspect (flux, separation efficiency, mechanical sustainability). All in all, P(VDF-co-HFP) VIPS membranes appear to be ideal materials for fast and effective gravity-driven separation of oil-rich emulsions.

Effect of Pluronic F127 on porous and dense membrane structure formation via non-solvent induced and evaporation induced phase separation

Novel porous and dense membranes based on polysulfone (PSF) modified by poly(ethylene glycol)–b–poly(propylene glycol)–b– poly(ethylene glycol) (Pluronic F127) were developed. The influence of Pluronic F127 introduction to the casting solution on different types of polymer membrane formation via two different phase inversion techniques—non-solvent induced phase separation (NIPS) for porous membranes and evaporation induced phase separation (EIPS) for dense membranes—was investigated. According to the triangular phase diagram obtained, PSF-Pluronic F127-N,N-dimethylacetamide (DMAc) systems feature lower critical solution temperature and have a tendency to micelle formation due to Pluronic F127 self-assembly. The structure, hydrophilic-hydrophobic balance and physicochemical properties of PSF-Pluronic F127 membranes were characterized by water contact angle measurements, scanning electron microscopy, nuclear magnetic resonance, small-angle X-ray scattering, and atomic force microscopy. The performance of dense membranes in pervaporation separation of water-ethyl acetate mixtures was investigated to reveal the effect of Pluronic F127 on the structure and free volume of the PSF-Pluronic F127 membranes. It was shown that Pluronic F127 introduction to the casting solution during membrane formation via two different techniques (NIPS and EIPS) leads to the increase in the pore size of the porous membranes and free volume of the dense membranes, as well as the increase in flux and surface hydrophilicity for both membrane types. Pluronic F127 was found to improve the antifouling performance of porous PSF-Pluronic F127 membranes in the BSA solution ultrafiltration. The introduction of 3 wt% Pluronic F127 into dense PSF membrane improved permeation flux in 1.7 and 2.7 times (15.1 and 27.3 g/(m2h)) at high selectivity level (100 wt% water in the permeate) during the separation of ethyl acetate-water mixtures (2 and 4 wt% ethyl acetate) compared to pristine PSF membrane.

Preparation of golf ball-shaped microspheres with fluorinated polycaprolactone via single-solvent electrospraying for superhydrophobic coatings

1H,1H,2H,2H-Perfluorooctyl polyacrylate (PTFOA) with a controllable molecular weight was successfully synthesized via atom-transfer radical polymerization (ATRP) followed by condensation with polycaprolactone (PCL) to obtain a new fluorinated block copolymer. Then, the copolymer PCL-b-PTFOA was processed via single-solvent electrospraying in chloroform to fabricate hierarchically porous microspheres. The microsphere size could be controlled from 5.13 ± 0.51 μm to 8.61 ± 0.90 μm, and the pore size on the microsphere surface could be controlled from 282.5 ± 42.0 nm to 603.3 ± 99.6 nm. Solvent evaporation-induced phase separation and fluorinated segment migration are the major reasons for the formation of the golf ball-shaped microspheres. In this study, the influence of electro-spraying parameters on the size and morphology of the porous microspheres was systemically studied. The golf ball-shaped microspheres significantly improved the surface roughness and the CA of their coatings reached 167.3 ± 1.7°. Furthermore, a superhydrophobic fabric was produced by pretreating cotton fabric with adhesive followed by coating with PCL-b-PTFOA via electrospraying. The robust superhydrophobicity can be obtained by the stable binding of PCL-b-PTFOA microspheres onto the fibers, with the CA reaching 155.3 ± 1.1°. Electrospraying of the fluoropolymer microsphere coating was proven to be a very promising technique to produce superhydrophobic coatings on textiles through a simple procedure.

Biomimetic Polymer Film with Brilliant Brightness Using a One‐Step Water Vapor–Induced Phase Separation Method

AbstractThe scales of the white Cyphochilus beetles are endowed with unusual whiteness arising from the exceptional scattering efficiency of their disordered ultrastructure optimized through millions of years of evolution. Here, a simple, one‐step method based on water vapor–induced phase separation is developed to prepare thin polystyrene films with similar microstructure and comparable optical performance. A typical biomimetic 3.5 µm PS film exhibits a diffuse reflectance of 61% at 500 nm wavelength, which translates into a transport mean free path below 1 µm. A complete optical characterization through Monte Carlo simulations reveals how such a scattering performance arises from the scattering coefficient and scattering anisotropy, whose interplay provides insight into the morphological properties of the material. The potential of bright‐white coatings as smart sensors or wearable devices is highlighted using a treated 3.5 µm film as a real‐time sensor for human exhalation.

Controlled Phase Separation in Poly( p-phenyleneethynylene) Thin Films and Its Relationship to Vapor-Sensing Properties.

In this paper, we report the synthesis and mesoporous film formation of hydrophobic rodlike poly( p-phenyleneethynylene)s (PPEs) and present porosity-dependent quenching studies using 1,3,5-trinitrotoluene (TNT) vapors. Nonsolvent vapor-induced phase separation was used to induce pore formation during film casting, and the concentration of PPEs in the casting solution was controlled carefully to prevent excimer formation. We found that the structures of the sidechains of the PPEs strongly influence the range of relative humidity at which controlled pore generation occurs, which could be rationalized from interfacial energies calculated from contact angle measurements. Porosity of the PPE films resulted in increased efficiency of fluorescence quenching toward TNT vapors, which previously required very thin films (below 5 nm) for sensing applications. The control of the porous structure as well as film thickness constitutes a promising strategy for enhancing the efficiency of chemosensors and in more general applications requiring fine-tuned polymer-gas interactions.

Preparation and Characterization of TiO₂-PVDF/PMMA Blend Membranes Using an Alternative Non-Toxic Solvent for UF/MF and Photocatalytic Application.

The approach of the present work is based on the use of poly (methylmethacrylate) (PMMA) polymer, which is compatible with PVDF and TiO2 nanoparticles in casting solutions, for the preparation of nano-composites membranes using a safer and more compatible solvent. TiO2 embedded poly (vinylidene fluoride) (PVDF)/PMMA photocatalytic membranes were prepared by phase inversion method. A non-solvent induced phase separation (NIPS) coupled with vapor induced phase separation (VIPS) was used to fabricate flat-sheet membranes using a dope solution consisting of PMMA, PVDF, TiO2, and triethyl phosphate (TEP) as an alternative non-toxic solvent. Membrane morphology was examined by scanning electron microscopy (SEM). Backscatter electron detector (BSD) mapping was used to monitor the inter-dispersion of TiO2 in the membrane surface and matrix. The effects of polymer concentration, evaporation time, additives and catalyst amount on the membrane morphology and properties were investigated. Tests on photocatalytic degradation of methylene blue (MB) were also carried out using the membranes entrapped with different concentrations of TiO2. The results of this study showed that nearly 99% MB removal can be easily achieved by photocatalysis using TiO2 immobilized on the membrane matrix. Moreover, it was observed that the quantity of TiO2 plays a significant role in the dye removal.

Porous poly(vinylidene fluoride) membranes with tailored properties by fast and scalable non-solvent vapor induced phase separation

Hydrophobic and highly porous poly(vinylidene fluoride) (PVDF) membranes with isotropic cross section as well as tunable and narrow barrier pore size distribution in the range from ~0.1 to ~1 µm have been prepared using the non-solvent vapor induced phase separation (VIPS) technique. The process conditions have been tuned to suit an industrial scale up, using a short production time and dimethyl sulfoxide (DMSO) as solvent for PVDF, instead of commonly used hazardous chemicals. Factors like kind of solvent, the relative humidity of air, the exposure time to humid air and the mass fraction of PVDF in the casting solutions have been used to tune membrane characteristics. Interestingly, it was revealed that DMSO as a less common solvent for PVDF shows better qualities regarding upscaling than other more frequently used polar aprotic solvents (e.g. dimethylacetamide) when using VIPS under suited conditions. The phenomenon was explained through investigations of the membrane formation step, in particular by water uptake and cloud point measurements, as well as structure and performance analyses, e.g. by scanning electron microscopy, gas flow/liquid dewetting permpometry, gas and water vapor permeability analyses and liquid water entry pressure measurements. Lab-scale manufactured membranes showed pore characteristics and performance desired for membrane contactor applications. Furthermore, fabrication on a roll-to-roll machine using a nonwoven support and the established VIPS conditions was realized in a short manufacturing time; resulting membranes structure and characteristics were found to be similar to the ones for the lab-scale membranes. Overall, the combination of PVDF with DMSO gives promising opportunities for a more eco-friendly industrial fabrication of porous membranes with advanced properties via VIPS.

Octadecylsilyl-bonded silica based novel solid phase extraction membranes

Octadecylsilyl-bonded silica based novel solid phase extraction membranes were fabricated by non-solvent vapor induced phase separation method for the first time, and employed for extraction trace phenol as a model. The effects of membrane fabrication conditions and extraction parameters on the recoveries were explored. Under the optimized fabrication conditions, the extraction recovery of phenol (0.02 mg/L, 100 mL) attains 100% with enrichment factor of 10. The spike recovery of real water samples reaches 97.67%–99.40% with standard deviation of 1.16%–1.42%, demonstrating great potential in solid phase extraction.

A novel smart membrane with ion-recognizable nanogels as gates on interconnected pores for simple and rapid detection of trace lead(II) ions in water

A novel smart membrane with ion-recognizable nanogels as gates on interconnected pores is developed for simple and rapid detection of trace lead(II) ions in water. The membrane is prepared via one-step vapor-induced phase separation (VIPS) method, and featured with interconnected porous structure and Pb2+-responsive poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) nanogels on polyethersulfone (PES) membrane pore surfaces as gates. Afforded by such a unique architecture, both high flux and significant responsive characteristics are achieved. With the proposed strategy, the nanogels are fixed onto the membrane pore surfaces during the formation of interconnected porous structure; thus, the immobilization of nanogels onto the membrane pore surfaces does not result in the decrease of pore sizes. The water fluxes of fabricated membranes could be even higher than 6000 kg m−2 h−1 driven by the static pressure of 20 cm water column under gravity at 34 °C, because of the three-dimensionally interconnected porous structures. Due to high sensitivity and selectivity of PNB nanogels on the membrane pore surfaces in response to Pb2+ ions, the fabricated membranes can efficiently detect Pb2+ ions with a limit of detection as low as 10−9 mol/L. With the proposed novel membrane, rapid detection of trace lead(II) ions in water can be easily achieved by simply monitoring the trans-membrane flux change in a gravity-driven membrane module device, which is highly potential and promising in real-time and easy-to-popularize monitoring of drinking water safety and may expand the scope of applications of facile detection techniques.

Tailoring pore distribution in polymer films via evaporation induced phase separation.

By considering a mixture of poly(methyl methacrylate)–tetrahydrofuran–water (PMMA–THF–H2O), we report an experimental approach to tune the distribution of pores in polymer films formed via evaporation induced phase separation (EIPS). We show that the drying induced composition and microstructural changes that occur due to the evaporation of the solvent (THF) and the nonsolvent (H2O) delineate the ultimate polymer film morphology. The temporal evolution of the microstructure, the phase behavior and the change in the composition of the PMMA–THF–H2O mixture at air–solution (top surface) and solution–substrate (bottom surface) interfaces is monitored to provide insights into the origin of the pore distribution in the final polymer films. The effects of various parameters such as nonsolvent and polymer concentration in the casting solution, casting solution thickness, relative humidity and temperature on the final film morphology are investigated to correlate how the composition path (CP) change under various conditions ultimately dictates the film morphology. We show that depending on the change in the composition of the polymer solution (evolution of CP) and the water/PMMA ratio at the time of phase separation, the morphology of the final film formed varies as – (1) non porous i.e., dense film (2) a film with pores only at the bottom surface (3) an asymmetric film i.e., films with a top dense layer (non-porous) supported by porous sub-layers (4) a porous film with uniform pores distributed across the entire film thickness and (5) a film with pores only at the top surface. In addition, we show that the morphology of the PMMA film can also be tuned by varying the composition of low and high molecular weight PMMA in the casting solution. These porous PMMA structures, being biocompatible, are useful for applications in cell culture, drug delivery and wound dressing.

Carrier Selection in Liquid Membrane for Extraction of Levulinic Acid using Hybrid Graphene-Polyethersulfone Supported Liquid Membrane

Abstract Levulinic acid (LA) and its valuable derivatives are growing demand in various applications such as in pharmaceuticals, food additives, agriculture, cosmetics, plasticizers and other industries. LA can be prepared through degradation of hexose from lignocellulosic biomass by using acids. However, the cost for LA recovery was higher than the production cost and some separation technique raise some environmental problem. Thus, it is essential to develop an economical separation process which can resulted in high yield of LA recovery with low cost and had less impacted to the environment. In this study, five different type of carriers were investigated during organic liquid membrane formulation which are tri-n-octyl phosphine oxide (TOPO), Aliquat 336, trioctylamine (TOA), tridodecylamin (TDA) and mixture of 50% TOA and 50% TDA. Hybrid graphene- polyethersulfone flat sheet membrane was prepared through vapour-induced phase separation and used as membrane support in the SLM process. The extraction was conducted using 10 g/L aqueous LA solution for 8 hours in the SLM system. The best carrier for extraction of LA was achieved using TOA which showed 74% of LA recovery. The LA extraction using TOPO, TDA, Aliquat 336, and mixture of TOA/TDA were 22%, 47%, 62%, and 67%, respectively. The selection of the carrier in liquid membrane formulation is important for achieving high recovery of LA using SLM process.

Preparation and characterisation of poly(butylene succinate) microcarriers containing pesticide

Microcarriers containing pesticide have been designed to improve drug stability and increase release efficiency, which is favourable to the environment and agriculture development. In this work, biodegradable poly(butylene succinate) microspheres containing pesticide, λ-cyhalothrin, as an active agent are prepared by the solvent evaporation induced phase separation method. The microspheres show a uniform morphology and a narrow particle size distribution. The pesticide content is measured by high-performance liquid chromatography. The prepared microcarriers demonstrate high-loading capacity, encapsulation efficiency and long release time, which may find potential applications as new pesticide formulations.