Inhibiting the concentration polarization of FO membranes based on the wettable microporous supporting layer and the enhanced dense skin layer

A novel thin film composite‐type forward osmosis (FO) membrane with inhibited concentration polarization phenomenon and expectant separation performance was prepared by continuous interfacial polymerization method. The nylon‐6,6 microfiltration membrane with the average pore size of 5 μm and the self‐wetting property was for the first time used as the supporting layer of the FO membranes, which decreased the mass transfer resistance in the porous supporting layer. The skin layer was prepared via the continuous interfacial polymerization of polyamide as a relatively dense layer, with the reverse salt flux of less than 1 g/m^?2 h^?1. The mass transfer resistance and the reverse salt flux of the prepared FO membranes were remarkably reduced due to the functional design of the double‐layer structure, which effectively enhanced the separation selectivity and restrain the concentration polarization of the FO membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45133.     

Investigating the membrane morphology of water/solvent/nylon 6 systems

In this study, nylon 6 membranes were prepared in a water coagulation bath with two types of solvents, CaCl₂–methanol (CaClMe) and formic acid (FA). The morphology of the membranes, which was controlled by the phase behavior of their solutions, were connected to the mechanism of demixing, including liquid–liquid and liquid‐crystallization. Ternary phase diagrams showed that the CaClMe system coagulated significantly faster than the FA system. As observed by scanning electron microscopy, the CaClMe membrane had a porous, interconnected pore structure with macrovoids, whereas the FA membrane had a dense, spherulitic surface with a closed cell morphology. The high reaction surface of the CaClMe membrane with dye molecules provided outstanding dye rejection. Also, thermal analysis by differential scanning calorimetry showed that the slow coagulation of the FA system facilitated the formation of stable α‐form crystals rather than a metastable γ‐form structure. The results show that the phase‐separation mechanism was switched from liquid–liquid to liquid‐crystallization through a change in the solvent type from CaClMe to FA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Developing thin‐film‐composite forward osmosis membranes on the PES/SPSf substrate through interfacial polymerization

A new scheme has been developed to fabricate high‐performance forward osmosis (FO) membranes through the interfacial polymerization reaction on porous polymeric supports. p‐Phenylenediamine and 1,3,5‐trimesoylchloride were adopted as the monomers for the in‐situ polycondensation reaction to form a thin aromatic polyamide selective layer of 150 nm in thickness on the substrate surface, a lab‐made polyethersulfone (PES)/sulfonated polysulfone (SPSf)‐alloyed porous membrane with enhanced hydrophilicity. Under FO tests, the FO membrane achieved a higher water flux of 69.8 LMH when against deionized water and 25.2 LMH when against a model 3.5 wt % NaCl solution under 5.0 M NaCl as the draw solution in the pressure‐retarded osmosis mode. The PES/SPSf thin‐film‐composite (TFC)‐FO membrane has a smaller structural parameter S of 238 μm than those reported data. The morphology and topology of substrates and TFC‐FO membranes have been studied by means of atomic force microscopy and scanning electronic microscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effects of γ‐aminopropyltriethoxylsilane on morphological characteristics of hybrid nylon‐66‐based membranes before electron beam irradiation

Nylon‐66 is a typical semicrystalline polymer that can be crosslinked using crosslinking agents and electron beam irradiation. Hybrid nylon‐66‐based membranes are more porous but denser compared to the pure nylon‐66 membrane. Besides that, hybrid nylon‐66 membranes exhibit higher water uptake and severe swelling in water. Si/nylon‐66 membranes were prepared by adding γ‐aminopropyltriethoxylsilane (APTEOS). Crosslinked silica in nylon‐66 membranes is confirmed with high gel content and Fourier transform infrared peaks, but XRD results showed that there is a low crystalline degree in these membranes. The thermal stability of hybrid nylon‐66 membranes is also less affected by APTEOS. The crosslinking agent only improves storage modulus in hybrid nylon‐66 membranes. After irradiation, it is learned that APTEOS improves separation performance of nylon‐66 membranes. However, excessive APTEOS causes the ratio of effective thickness over porosity (Δx/A_k) reduces significantly resulting a lower permeability membrane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Suppression of gold nanoparticle agglomeration and its separation via nylon membranes

Use of ultraporous nylon membrane is one of the most widely employed techniques for removal of hard and soft nanoparticles in the semiconductor industry,and the accurate determination of membrane pore size is necessary in order to avoid manufacturing defects caused by contamination.The gold nanoparticle has several benefits for the evaluation of polymeric membranes;however,the nanoparticles agglomerate easily on the nylon membrane and make it difficult to evaluate the membrane precisely.The properties of 2-amino-2-hydroxymethyl-1,3-propanediol (ADP) ligand in gold nanoparticle solution were systematically investigated,and ADP was utilized for improved evaluation of the nylon membranes.Nylon membrane used in this study was prepared by phase inversion techniques.Ultrathin dense layer on top of the membrane surface and Darcy structures in the microporous membrane support were observed.The gold particle rejection was carried out at various pH values from 4 to 14 and higher rejection was observed at pH 4 and 8.The suppression of gold colloid agglomeration using ADP and monodispersity of gold colloids was also analyzed by confocal laser scanning microscopy (CLSM),transmission electron microscopy (TEM),and scanning electron microscopy (SEM).van der Waals interaction energy of the particles was reduced in the addition of ADP.The presence ofADP ligand in the gold solutions prevented the agglomeration of gold nanoparticles and reduced the adsorption of the particles on the nylon membrane surface,leading to precise evaluation of membrane pore sizes.     

Advanced porous polyphenylsulfone membrane with ultrahigh chemical stability and selectivity for vanadium flow batteries

Porous polyphenylsulfone (PPSU) membranes are facilely prepared via the nonsolvent-induced phase separation method. The typical asymmetric structure of such prepared porous membranes can be controlled by optimizing the sulfonation degree of the sulfonated poly(ether ether ketone) to 84.7% in the casting solution. Scanning electron microscopy images show that the porous membrane comprises a thin dense top skin layer, a sublayer structure with distinct long finger-like pores and the large pores in the substructure. The porous PPSU membrane was then used in vanadium flow battery (VFB). The optimized porous membrane yields an admirable performance, including excellent selectivity, chemical stability, and high columbic efficiency. Furthermore, the low cost of porous PPSU membranes indicates the promise of this technology for use in VFB applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47752.     

SPG膜乳化与界面聚合法制备单分散多孔微囊膜

小粒径单分散中空储库结构微囊膜的制备具有重要学术意义和实用价值。为此采用了SPG(Shirasu-Porous-Glass)膜乳化法和界面聚合法，对小粒径单分散多孔微囊膜的制备进行了较系统的实验研究，以期为进一步制备多孔内接枝环境感应型功能凝胶开关的小粒径单分散微囊型靶向式药物载体提供基体。研究结果表明，采用SPG膜乳化法可制得单分散性良好的乳液液滴，进而采用界面聚合法可得到单分散微囊。用膜乳化方法易于控制乳液液滴及微囊的大小，在研究中SPG膜乳化法制备的乳液液滴及微囊的平均粒径大约是所用膜孔径的3．6倍。微囊膜的多孔性可以靠改变溶剂和单体的成分来进行控制，扫描电镜检测结果表明所制备出的不同粒径级别的单分散微囊膜均具有良好的多孔结构。     

Sulfonated polyphenylsulfone asymmetric membranes: Effect of coagulation bath (acetic acid‐NaHCO3/isopropanol) on morphology and antifouling properties

Sulfonated polyphenylsulfone porous asymmetric membranes, S‐PPSU with different sulfonation degrees, 21, 33, 50 wt %, were prepared by phase inversion. Two different coagulation baths were explored for asymmetric membrane preparation: acetone/isopropanol and acetic acid (AA)‐NaHCO₃/isopropanol. The latter bath allows better morphology control for the nucleation and pore formation of the membrane. Scanning electron microscopy of membranes shows that pore interconnectivity is improved, when the mixture of AA‐NaHCO₃/isopropanol was used for asymmetric S‐PPSU ultrafiltration membranes preparation. S‐PPSU asymmetric membranes show an increasing hydrophilicity with increasing sulfonation degree. Asymmetric membrane antifouling properties improve as the concentration of sulfonic groups increases in the membrane showing twice the flux recovery ratio and lower BSA protein absorption in static and dynamic flux tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44502.     

Distribution and diffusion coefficients of NaCl in polyamide (nylon‐6,6 and polyxylyleneadipamide) membranes

Thin membranes of an aliphatic polyamide (nylon‐6,6) and an aromatic polyamide (polyxylyleneadipamide) (PXAP) were prepared, and their distribution (K) and overall diffusion (D) coefficients of sodium chloride were measured with the unsteady‐state and steady‐state dialysis method. The overall diffusion coefficients at a zero concentration [D⁽⁰⁾] of sodium chloride for nylon‐6,6 and PXAP were 1.3–0.8 μm²/s (from 2 min of interfacial polymerization to 4 min) and 0.078, respectively. D⁽⁰⁾ for PXAP was about 3 times greater than that of a cellulose acetate (CA) membrane (0.024 μm²/s). The K values for nylon‐6,6 and PXAP were 0.7–0.5 from 2 to 4 min and 0.05, respectively. K for PXAP was almost the same as K for CA (0.06). A two‐part (dense and porous) model of the membrane structure was applied to obtain D_d (the diffusion coefficient in the dense part of the membrane) and D_p (the diffusion coefficient in the porous part of the membrane) for CA, PXAP, and nylon‐6,6 thin membranes. The values of D_d were almost the same for both nylon‐6,6 and PXAP (0.05–0.061 μm²/s) and about 10 times greater than the value for the CA membrane (5.6 × 10^?3 μm²/s). D_p for PXAP was almost the same as D_p for CA. However, D_p for the nylon‐6,6 membrane was 10–16 times greater than D_p for the PXAP membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2605–2612, 2002     

Improving the charged and antifouling properties of PVDF ultrafiltration membranes by blending with polymerized ionic liquid copolymer P(MMA‐b‐MEBIm‐Br)

This study describes the fabrication and properties of poly(vinylidene fluoride) (PVDF) filtration membranes modified by blending with ionic liquid block copolymer P(MMA‐b‐MEBIm‐Br), which is synthesized via reversible addition‐fragmentation chain transfer polymerization method. The attenuated total reflectance‐Fourier transform infrared spectroscopy and X‐ray photoelectron analyses reveal that the ionic liquid block copolymers are immobilized on PVDF membrane surface. The modified PVDF membrane exhibits excellent charged and antifouling properties because of the charged and hydrophilic properties of the copolymer. Scanning electron microscopy and atomic force microscopy also indicate the morphological characteristics of the membrane and demonstrate that the surface porous structure becomes denser after adding the copolymer. The data of filtration and the zeta potential of the membranes suggest that the charged properties of the ionic liquid block copolymers are mainly responsible for the improvement of the reversible fouling ratio and the decrease in the total fouling ratio of the membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44751.     

Synthesis and characterization of poly(acrylic acid‐co‐N‐[3‐(dimethylamino)propyl]‐methacrylamide) hydrogel membranes for biomedical applications

A series of new hydrogel membranes with different compositions of acrylic acid (AAc) and N‐[3‐(dimethylamino)propyl]‐methacrylamide (DMAPMA) were prepared by aqueous copolymerization, without using chemical crosslinker or radiation. Chemical structure of the membranes (PADMAs) was characterized by Fourier transform infrared spectroscopy (FTIR). Swelling experiments were carried out in simulated body fluid (SBF) at 37 ± 1°C to investigate degree of swelling, dimensional stability, and pore size of the PADMA membranes. In SBF, the variation of pore size with membrane composition was monitored by optical microscopic technique. Morphology of the membranes was characterized, before and after exposure to SBF, by scanning electron microscopy (SEM). It was observed that the membranes are composed of closely packed nanogels of ～200 nm. Macroporous network structure of the SBF‐swollen PADMA was also observed to be composed of interconnected nanogels. Blood compatibility of the PADMA membranes was evaluated in vitro, by performing hemolysis assay and thrombogenicity assay. The extent of hemolysis due to PADMA membranes was found to be <2%, which ensured that all of the membranes were highly hemocompatible. Salicylic acid (SA) was chosen as a model drug. Diffusion coefficient of SA through PADMA membranes was investigated. It was observed that membrane composition regulates both pore size and drug diffusion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fabrication of Palladium Membranes Supported on a Silicalite‐1 Zeolite‐Modified Alumina Tube for Hydrogen Separation

Thin palladium membranes were fabricated on macroporous α‐Al₂O₃ tubes by electroless plating. The silicalite‐1 (Sil‐1) zeolite serving as intermediate and diffusion barrier layer was introduced to modify the surface roughness and pore size of the porous substrate and prevent the atomic interdiffusions of the metal elements between Pd layer and the support. The Pd composite membranes were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and electron probe microanalysis (EPMA), revealing that morphology and structure of the Sil‐1 layer significantly influence the Pd membrane preparation. Single‐gas permeation tests were carried out with gas H₂ and N₂ to determine the permeation performance of the membranes. The resulting membrane exhibited long‐term stability under hydrogen permeation.     

Preparations of metal impregnated porous inorganic membranes for hydrogen separation by multi-step pore modifications

In this research, porous inorganic membranes for hydrogen separation were prepared with α-alumina support by multi-step pore modification method. Porous inorganic membranes were made by three consecutive steps: sol-gel method,in-situ hydrolysis of tetraethylorthosilicate (TEOS) and soaking and vapor deposition (SVD) method. In order to enhance the hydrogen selectivity, we used nickel (Ni) and palladium (Pd) particles in the first and final pore modification steps. Although both nickel and palladium induced surface diffusion, palladium was shown more effective for hydrogen selective adsorption than nickel. This multi-step method produced porous membranes with a moderate hydrogen selectivity and excellent hydrogen permeability at high temperature up to 773 K and at transmembrane pressure (ΔP) as high as 310 kPa. The separation factor of hydrogen relative to nitrogen was maintained at about 7 even when the transmembrane pressure was 70 kPa, and the hydrogen permeability was still much higher than that of non-porous polymeric membranes. Furthermore, the distributions of nickel and palladium within the intermediate layer formed at the membrane cross-section were examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis.     

Tailoring of a γ-Alumina Membrane with a Bimodal Pore Size Distribution for Improved Permeability

Porous γ-alumina with a bimodal pore size distribution has been developed by adding nanosized polystyrene beads to boehmite sol as templating units. The primary pore diameter is in the range of 4–6 nm and the secondary pore diameter is ca. 50 nm with minor pore shrinkage. The unsupported γ-alumina with different porous structures are characterized using thermogravimetric analysis, Fourier transform infrared spectra, X-ray diffraction, N₂ adsorption/desorption, and transmission electron microscopy. γ-alumina with a bimodal porous structure shows reduced transport resistance compared with γ-alumina with a unimodal porous structure in the dye adsorption test. Although the thickness of γ-alumina thin layer increases when more secondary pores are generated, a γ-alumina membrane with a bimodal pore size distribution shows diminution of transport resistance in the water permeability study also.     

A new spectroscopic approach to characterization of porous and filled polymeric materials

An effective and simple spectroscopic method is proposed for determining the degree of filling and porosity of polymeric materials and the distribution of the filler particle or pore size in the polymer matrix is proposed and consists of separation and analysis of absorbing and scattering components of the radiation falling on the sample. The possibilities and advantages of the spectroscopic approach in comparison to visual methods of optical and electron microscopy are demonstrated on a wide range of objects (track membranes, porous xerogel films, polymer composites and blends, etc.). Translated from Khimicheskie Volokna, No. 3, pp. 63–71, May–June, 2008.     

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

In this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44444.     

Effects of Poly(Vinyl Alcohol) Content and Calcination Temperature on the Characteristics of Unsupported Alumina Membrane

Abstract

Nonsupported alumina porous membranes without pinholes or cracks were prepared by the sol-gel process using aluminum sec-butoxide as the starting material. The effects of using different PVA contents at various calcination temperatures on the characteristics of the membrane were investigated by scanning electron microscopy and nitrogen sorption porosimetry. The results after calcining at 450°C for 5 hours showed that the range of pore size distributions increases with increasing PVA concentration. The active nucleus numbers of phase transition to α-alumina decreased as the content of PVA increased at about 1050°C. The morphology of unsupported alumina membranes was affected by the PVA concentration and calcination temperature.     

ZIF‐8 SURMOF Membranes Synthesized by Au‐Assisted Liquid Phase Epitaxy for Application in Gas Separation

Metal‐organic frameworks (MOFs) exhibit a huge potential for gas separation. ZIF‐8 is an interesting candidate due to its high thermal stability and its pore properties. By liquid phase epitaxy, the growth of the highly oriented surface‐anchored MOF ZIF‐8 on non‐porous and porous surfaces has been proven. The preparation of monolithic ZIF‐8 thin films supported by porous α‐Al₂O₃ substrates modified by a thin layer of Au is investigated. The layer‐by‐layer deposition process accomplished via a dipping procedure results in the formation of defect‐ or crack‐free membranes, preliminary characterized by the determination of ethane and ethene permeance.     

Effect of diluents on the crystallization behavior of poly(4‐methyl‐1‐pentene) and membrane morphology via thermally induced phase separation

The effect of diluents on polymer crystallization and membrane morphology via thermally induced phase separation(TIPS) were studied by changing the composition of the mixed‐diluents systematically, in the system of poly(4‐methyl‐1‐pentene) (TPX)/dibutyl‐phthalate (DBP)/di‐n‐octyl‐phthalate (D‐n‐OP) with TPX concentration of 30 wt %. The TPX crystallization was observed with differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). The membranes were characterized with scanning electron microscopy (SEM), porosity, and pore size measurement. As the content of D‐n‐OP increased in mixed‐diluents, the solubility with TPX increased, inducing the phase separation changing from liquid–liquid phase separation into solid–liquid phase separation, which changed the membrane morphology and structure. When the ratios of DBP to D‐n‐OP were 10 : 0, 7 : 3; 5 : 5, and 3 : 7, membranes were formed with cellular structure and well connected pores, while the ratio was 0 : 10, discernable spherulities were found with not well‐formed pore structure. The effect of composition of the mixed‐diluents on membrane morphology was more remarkable in TPX/dioctyl‐sebacate (DOS)/dimethyl‐phthalate (DMP) system, since good cellular structure was formed when the ratios of DOS to DMP were 10 : 0, 7 : 3, while spherulites were observed when 5 : 5. Dual endotherm peaks behavior on DSC melting curves emerged for all the samples in this study, which was attributed to the special polymer crystallization behavior, primary crystallization, and secondary crystallization occurred when quenching the samples. As the content of D‐n‐OP increased, the secondary crystallization enhanced which induced the first endotherm peak on DSC melting curves moving to a lower temperature and the broadening of the overall melting peak, as well as the increasing of the overall crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimization of structure and properties of polyphenylene sulfide porous membrane by controlling the process of thermally induced phase separation

Polyphenylene sulfide (PPS) porous membranes were successfully prepared from miscible blends of PPS and polyethersulfone (PES) via thermally induced phase separation followed by subsequent extraction of the PES diluent. The morphologies, crystalline structures, mechanical properties, pore structures and permeate fluxes of the PPS porous membranes obtained from different phase separation processes were characterized and are discussed. During the phase separation in the heating process, PPS and PES mainly underwent liquid–liquid phase separation, and then a nonhomogeneous porous structure with a mean pore size of 100 μm and a honeycomb‐like internal structure formed on the membrane surface. The phase separation of PPS/PES occurring in the cooling process was easier to control and the related pore diameter distribution was more regular. In the process of direct annealing, as the phase separation temperature decreased, the pore size distribution became more homogeneous and the mean diameter of the pores also decreased gradually. When the phase separation temperature decreased to 200 °C, PPS membranes with a network structure and a uniform as well as well‐interconnected porous structure could be obtained. In addition, the maximum permeation flux reached 1718.03 L m^–2 h^–1 when the phase separation temperature was 230 °C. The most probable pore diameter was 6.665 nm, and the permeate flux of this membrane was 2.00 L m^–2 h^–1; its tensile strength was 17.07 MPa. Finally, these PPS porous membranes with controllable pore structure as well as size can be widely used in the chemical industry and energy field for liquid purification. © 2020 Society of Chemical Industry