In‐situ cross‐linked PVDF membranes with enhanced mechanical durability for vacuum membrane distillation

A novel and effective one‐step method has been demonstrated to fabricate cross‐linked polyvinylidene fluoride (PVDF) membranes with better mechanical properties and flux for seawater desalination via vacuum membrane distillation (VMD). This method involves the addition of two functional nonsolvent additives; namely, water and ethylenediamine (EDA), into the polymer casting solution. The former acts as a pore forming agent, while the latter performs as a cross‐linking inducer. The incorporation of water tends to increase membrane flux via increasing porosity and pore size but sacrifices membrane mechanical properties. Conversely, the presence of EDA enhances membrane mechanical properties through in‐situ cross‐linking reaction. Therefore, by synergistically combining the effects of both functional additives, the resultant PVDF membranes have shown good MD performance and mechanical properties simultaneously. The parameters that affect the cross‐link reaction and membrane mechanical properties such as reaction duration and EDA concentration have been systematically studied. The membranes cast from an optimal reaction condition comprising 0.8 wt % EDA and 3‐hour reaction not only shows a 40% enhancement in membrane Young's Modulus compared to the one without EDA but also achieves a good VMD flux of 43.6 L/m²‐h at 60°C. This study may open up a totally new approach to design next‐generation high performance MD membranes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4013–4022, 2016     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of PVDF/poly(tetrafluoroethylene‐co‐vinyl alcohol) blend membranes with antifouling propensities via nonsolvent induced phase separation method

Poly(vinylidene fluoride) (PVDF) was blended with a new amphiphilic copolymer, poly(tetrafluoroethylene‐co‐vinyl alcohol) [poly(TFE‐VA)], via non‐solvent induced phase separation (NIPS) method to make membranes with superior antifouling properties. The effects of the VA/TFE segment ratio of the copolymer and the copolymer/PVDF blend ratio on the properties of the prepared membranes were studied. Membranes with similar water permeabilities, surface pore sizes, and rejection properties were prepared and used in bovine serum albumin (BSA) filtrations with the same initial water flux and almost the same operating pressure, to evaluate the sole effect of membrane material on fouling propensity. While the VA/TFE segment ratio strongly affected the membrane antifouling properties, the effects of the copolymer/PVDF blending ratio were not so drastic. Membrane surface hydrophilicity increased, and BSA adsorption and fouling decreased upon blending a small amount of amphiphilic copolymer with a high VA/TFE segment ratio with PVDF (copolymer/PVDF blending ratio 1:5). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43780.     

Preparation of PVDF hollow‐fiber membranes via immersion precipitation

Porous polyvinylidene fluoride (PVDF) hollow‐fiber membranes with high porosity were fabricated using the immersion precipitation method. Dimethylacetamide (DMAc) and N‐methyl‐2‐pyrrolidone (NMP) were used as solvent, respectively. In addition, polyvinylpyrrolidone (PVP), lithium chloride, and organic acids were employed as nonsolvent additives. The effects of the internal and external coagulation mediums on the resulting membrane properties were also investigated. The resulting hollow‐fiber membranes were characterized in terms of maximum pore radius, mean pore radius, effective surface porosity as well as wetting pressure. The structures of the prepared hollow fibers were examined using a scanning electron microscope. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1643–1653, 2001     

Preparation of polyvinylidene fluoride membrane via a thermally induced phase separation using a mixed diluent

Polyvinylidene fluoride (PVDF) membranes were prepared via a thermally induced phase separation method with a mixed diluent (dibutylphthalate/dioctyl phthalate). The effects of PVDF concentration and cooling bath temperature (CBT) on the structure and properties of the membranes were investigated. Scanning electron microscopy photos showed that the cross‐section of all the membranes, regardless of PVDF concentration and CBT, presented a bi‐continuous structure with the spherulitic pattern; moreover, the spherulitic patterns became clear gradually from the top surface to the bottom surface, and the top surface was denser than the bottom surface. As a result, all the membranes exhibited an asymmetric structure. The membrane property measurement indicated that, as PVDF concentration increased from 25 to 35 wt %, the pure water flux (PWF) decreased from 342 to 80 L m^?2 h^?1, and the porosity decreased slightly, whereas the minimum bubble point pressure (BPP) increased, which indicates maximum pore size decreased. In addition, with the increase in CBT, the PWF increased, but, the minimum BPP and porosity decreased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of hot‐press on electrospun poly(vinylidene fluoride) membranes

Poly(vinylidene fluoride) (PVDF) was electrospun into ultrafine fibrous membranes from its solutions in a mixture of N,N‐dimethylformamide and acetone (9:1, v/v). The electrospun membranes were subsequently treated by continuous hot‐press at elevated temperatures up to 155°C. Changes of morphology, crystallinity, porosity, liquid absorption, and mechanical properties of the membranes after hot‐press were investigated. Results of scanning electron microscopy showed that there were no significant changes in fibrous membrane morphology when the hot‐press temperature varied from room temperature to 130°C, but larger pores were formed because of fibers melting and bonding under higher temperatures. Analyses of X‐ray diffraction and differential scanning calorimeter exhibited that the crystalline form of PVDF could transfer from β‐type to α‐type during hot‐press at temperatures higher than 65°C. Tensile tests suggested that the mechanical properties of the electrospun PVDF membranes were remarkably enhanced from 25 to 130°C, whereas the porosity and the liquid absorption decreased. The hot‐press at 130°C was optimal for the electrospun PVDF membranes. The continuous hot‐press post‐treatment could be a feasible method to produce electrospun membranes, not limited to PVDF, with suitable mechanical properties as well as good porosity and liquid absorption for their applications in high‐quality filtrations or battery separators. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Structuring and characterization of a novel microporous PVDF membrane with semi‐interpenetrating polymer networks for vacuum membrane distillation

In this paper, by using the non‐solvent induced phase separation (NIPS) process, a new microporous membrane with semi‐interpenetrating polymer network (semi‐IPN) was produced in which PDMS polymer is crosslinked and PVDF polymer is linear. For the fabrication of the membrane, tetraethylorthosilicate (TEOS) was used as the crosslinking agent and dibutyltin dilaurate (DBTDL) was used as the catalyst. By changing the mass ratio of PDMS/TEOS, the structure and the performance of the prepared membrane were studied. The membranes were also investigated by scanning electron microscopy (SEM‐EDX), X‐ray diffraction (XRD), attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy, capillary flow porometer, thermogravimetric analysis (TGA), water contact angle (WCA), etc. Through the experiments we found that the semi‐IPNs structure was more likely produce the sponge‐like pores and was more favorable to the mechanical properties, pore structure and thermal stability of the membranes. Using the PDMS–PVDF membranes for the VMD desalt of the NaCl solution (30 g/L), 99.9% salt rejection and reasonable fluxes were obtained, which make us believe that it could be possible to use the semi‐IPNs PDMS–PVDF membrane to treat real sea water for its desalt. POLYM. ENG. SCI., 57:1311–1321, 2017. © 2017 Society of Plastics Engineers     

High‐performance PDMS membranes for pervaporative removal of VOCs from water: The role of alkyl grafting

To improve the pervaporation performance of PDMS membrane, alkyl groups with different chain length were grafted into PDMS matrix. The prepared membranes were characterized by ATR‐IR, DSC, TGA, PALS, and tensile testing. The effects of alkyl grafting on pervaporation performance of PDMS membrane were investigated in separation of ethyl acetate/water mixture. Experimental results show that the separation factor of PDMS membrane is largely improved by alkyl grafting because of the enhanced preferential sorption of ethyl acetate, and this improvement depends on alkyl grafting ratio and alkyl chain length. The total flux of PDMS membrane reduces after alkyl grafting owing to the decreased free volume. When grafting ratio is above 6.9%, membrane grafted with shorter alkyl groups is preferred for pervaporation. The best pervaporation performance is achieved by 9% octyl grafted PDMS membranes with a separation factor of 592 and a total flux of 188 gm^?2 h^?1 in separation of 1% ethyl acetate/water mixture at 40 °C. Moreover, this octyl grafted PDMS membrane also exhibits excellent separation performance in removal of butyl acetate, methyl‐tert‐butyl ether, and n‐butanol from water. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43700.     

Preparation of high‐flux ultrafiltration membranes by blending strongly charged polymer

Three kinds of high‐flux ultrafiltration membranes were fabricated by blending strongly charged polymer [sulfonated poly(phenylene oxide) (SPPO)] with neutral polymer [cellulose acetate (CA), polyethersulfone (PES), or polyvinylidene fluoride (PVDF)]. After blending with SPPO, the pure water flux of CA‐SPPO, PES‐SPPO, and PVDF‐SPPO membrane increase by 3, 76, and 30 times at a transmembrane pressure of 100 kPa. Compared with the unblended membranes, the pore radius of CA‐SPPO, PES‐SPPO, and PVDF‐SPPO membrane increased from 31.9 to 33.2 nm, 26.1 to 28.6 nm, and 19.8 to 25.7 nm, respectively. The addition of strongly charged polymer decreased the thermodynamic stability of casting solutions, promoting the phase inversion process and resulting in highly porous structure. The charged groups and hydrophilicity of the polymer facilitate the formation of an additive concentration gradient (more additive in the active layer), endowing the blend membrane with better hydrophilicity and greater wettability gradient. The high porosity, good hydrophilicity, and larger wettability gradient enable the high permeation of blend membranes. This work shows how the strongly charged polymer affects the formation and performance of blend membrane, which will be useful for designing high‐performance membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44570.     

Structure formation and characterization of PVDF hollow fiber membranes by melt‐spinning and stretching method

Melt‐spinning and stretching (MS‐S) method was proposed for preparing poly(vinylidene fluoride) (PVDF) hollow fiber membranes with excellent mechanical properties. The morphology and properties of PVDF fibers and membranes were investigated by small angle X‐ray scattering (SAXS), differential scanning calorimeter (DSC), field emission scanning electron microscope, mercury porosimeter, and tensile experiment. SAXS results indicated that the stacked lamellar structure aligned normal to the fiber axis was separated and deformed when the fibers were strained, and the long period of the strained fibers increased accordingly. Factors affecting the membrane properties were mainly spin‐draw ratio, annealing temperature, time, and stretching rate. Experimental results showed that the average pore size, porosity, and N₂ permeation of the membranes all increased with the increasing spin‐draw ratios and annealing temperatures. Annealing the nascent PVDF hollow fibers at 145°C for 12 h was suitable for attaining membranes with good performance. In addition, the amount and size of the micropores of the membrane increased obviously with stretching rate. Tensile experiment indicated PVDF hollow fiber membranes made by MS‐S process had excellent mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Polydimethylsiloxane‐modified polyurethane–poly(ɛ‐caprolactone) nanofibrous membranes for waterproof,breathable applications

In this study, we prepared polydimethylsiloxane (PDMS)‐modified polyurethane–poly(?‐caprolactone) nanofibrous membranes with excellent waterproof, breathable performances via an electrospinning technique. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and mechanical testing were used to characterize the morphologies and properties of the composite nanofibers. The fiber diameter and porous structure of the membranes were regulated by the adjustment of the temperatures of thermal treatment and the PDMS concentrations. The fibrous membranes obtained at a typical temperature of 70 °C possessed an optimized fibrous structure with a diameter of 514 ± 2 nm, a pore size of 0.55–0.65 µm, and a porosity of 77.7%. The resulting nanofibrous membranes modified with 5 wt % PDMS were endowed with good waterproof properties (water contact angle = 141 ± 1°, hydrostatic pressure = 73.6 kPa) and a high breathability (air permeability rate = 6.57 L m^?2 s^?1, water vapor transmission rate = 9.03 kg m^?2 day^?1). Meanwhile, the membranes exhibited robust mechanical properties with a high strength (breakage stress = 11.7 MPa) and excellent thermal stability. This suggests that they would be promising candidates for waterproof, breathable applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46360.     

PDMS/PVDF microporous membrane with semi‐interpenetrating polymer networks for vacuum membrane distillation

In this article, using the non‐solvent induced phase separation process, a new microporous membrane with the semi‐interpenetrating polymer network (semi‐IPN) structure was produced. For this membrane, polydimethylsiloxane (PDMS) polymer is crosslinking and poly(vinylidene fluoride) (PVDF) polymer is linear, by changing the mass ratio of PDMS/PVDF, the structure and the performance of the prepared membranes were studied. The membranes were also investigated by attenuated total reflection‐Fourier transform infrared (ATR‐FTIR), scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, thermogravimetric analysis, and water contact angle, etc. ATR‐FTIR spectroscopy confirmed the formation of semi‐IPN; compared with the PDMS/PVDF polymer without semi‐IPNs structure, the viscosity of the semi‐IPNs structured casting solution increased, membrane mechanical property increased but its hydrophobicity decreased. Using the resulting membranes for the vacuum membrane distillation desalt of the NaCl solution (30 g/L), 99.9% salt rejection and reasonable flux were obtained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45792.     

Preparation and performance of the novel PVDF ultrafiltration membranes blending with PVA modified SiO2 hydrophilic nanoparticles

In this study, PVA‐SiO₂ was synthesized by modifying silica (SiO₂) with polyvinyl alcohol (PVA), then a novel polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane was prepared by incorporating the prepared PVA‐SiO₂ into membrane matrix using the non‐solvent induced phase separation (NIPS) method. The effects of PVA‐SiO₂ particle on the properties of the PVDF membrane were systematically studied by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), surface pore size, porosity, and water contact angle. The results indicated that with the addition of PVA‐SiO₂ particles in the PVDF UF membranes, membrane mean pore size increased from 80.06 to 126.00 nm, porosity improved from 77.4% to 89.1%, and water contact angle decreased from 75.61° to 63.10°. Furthermore, ultrafiltration experiments were conducted in terms of pure water flux, bovine serum albumin (BSA) rejection, and anti‐fouling performance. It indicated that with the addition of PVA‐SiO₂ particles, pure water flux increased from 70 to 126 L/m² h, BSA rejection increased from 67% to 86%, flux recovery ratio increased from 60% to 96%, total fouling ratio decreased from 50% to 18.7%, and irreversible fouling ratio decreased from 40% to 4%. Membrane anti‐fouling property was improved, and it can be expected that this work may provide some references to the improvement of the anti‐fouling performance of the PVDF ultrafiltration membrane. POLYM. ENG. SCI., 59:E412–E421, 2019. © 2018 Society of Plastics Engineers     

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes prepared from PVDF‐co‐HFP/PEG‐600Mw/DMAC solution for membrane distillation

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes were prepared by using the phase inversion method. The effect of polyethylene glycol (PEG‐600Mw) with different concentrations (i.e., 0, 5, 7, 10, 12, 15, 18, and 20 wt %) as a pore former on the preparation and characterization of PVDF‐co‐HFP hollow fibers was investigated. The hollow fiber membranes were characterized using scanning electron microscopy, atomic force microscopy, and porosity measurement. It was found that there is no significant effect of the PEG concentration on the dimensions of the hollow fibers, whereas the porosity of the hollow fibers increases with increase of PEG concentration. The cross‐sectional structure changed from a sponge‐like structure of the hollow fiber prepared from pure PVDF‐co‐HFP to a finger‐like structure with small sponge‐like layer in the middle of the cross section with increase of PEG concentration. A remarkable undescribed shape of the nodules with different sizes in the outer surfaces, which are denoted as “twisted rope nodules,” was observed. The mean surface roughness of the hollow fiber membranes decreased with an increase of PEG concentration in the polymer solution. The mean pore size of the hollow fibers gradually increased from 99.12 to 368.91 nm with increase of PEG concentration in polymer solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of nucleating agents on the morphologies and performances of poly(vinylidene fluoride) microporous membranes via thermally induced phase separation

The effects of nucleating agents on the morphology and performance of poly(vinylidene fluoride) (PVDF) microporous membranes via thermally induced phase separation were investigated. The nucleating agents studied were dicyclohexyl benzene amide (TMB‐5), 2,2‐methylene bis(4,6‐tertiary butyl phenol) sodium phosphate (TMP‐1), and 1,3 : 2,4‐di‐p‐methylbenzylidene sorbitol (DM–LO). Light transmittance experiments and differential scanning calorimetry (DSC) were performed to obtain phase diagrams of PVDF/tributyl citrate/di(2‐ethylhexyl) phthalate/nucleating agent doped solutions. The morphology and performance of the prepared PVDF microporous membranes were characterized with scanning electron microscopy and microfiltration experiments. The results show that the thermodynamics of liquid–liquid phase separation were not affected by the addition of the nucleating agents, but solid–liquid phase separation was influenced. The system with 0.3 wt % TMB‐5 had the fastest crystallization rate and a better nucleation ability. The PVDF microporous membranes had a partly closed, lacy bicontinuous structure with TMP‐1 and DM–LO, whereas the membrane with 0.3 wt % TMB‐5 had an interconnected bicontinuous structure. The pore size distribution became narrower with the addition of nucleating agent. With 0.3 wt % TMB‐5, the membrane had the minimum mean pore size (0.095 μm), a porosity of 80.3%, and a pure water flux of 270 L·m^?2·h^?1; these values were higher than those of the pure PVDF membrane. The performances of the membranes decreased with additions of TMB‐5 of greater than 0.3 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrospun poly(vinylidene‐fluoride)/POSS nanofiber membrane‐based polymer electrolytes for lithium ion batteries

In this study, poly(vinylidene fluoride) (PVDF)/polyhedral oligomeric silsesquioxanes (POSS) nanofibrous membranes are prepared through electrospun process. Field emission scanning electron microscope images clearly show that PVDF/POSS membranes have interconnected multi fibrous layers with ultrafine porous structures. The average fiber diameter and crystallinity of PVDF/POSS membranes are lesser than that of pure PVDF membrane. Thermal stability and electrolyte uptake of blend membranes increase with increasing POSS content. Finally, PVDF/POSS membranes are soaked in a liquid electrolyte to form the polymer electrolytes and are assembled in coin cells to test their electrochemical properties such as ionic conductivity, interfacial characteristics, and electrochemical stability windows. The ionic conductivity improves with increasing POSS content and the highest ionic conductivity reaches 2.91 × 10⁻³ S/cm at room temperature. It is also worth mention that the composite polymer electrolytes show low interfacial resistance and high electrochemical stability window of 5.6 V (vs. Li⁺ /Li) with storage time. POLYM. COMPOS., 38:629–636, 2017. © 2015 Society of Plastics Engineers     

Nanophase morphology and crystallization in poly(vinylidene fluoride)/polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene blends

An approach to achieve confined crystallization of ferroelectric semicrystalline poly(vinylidene fluoride) (PVDF) was investigated. A novel polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene (PDMS‐b‐PMMA‐b‐PS) triblock copolymer was synthesized by the atom‐transfer radical polymerization method and blended with PVDF. Miscibility, crystallization and morphology of the PVDF/PDMS‐b‐PMMA‐b‐PS blends were studied within the whole range of concentration. In this A‐b‐B‐b‐C/D type of triblock copolymer/homopolymer system, crystallizable PVDF (D) and PMMA (B) middle block are miscible because of specific intermolecular interactions while A block (PDMS) and C block (PS) are immiscible with PVDF. Nanostructured morphology is formed via self‐assembly, displaying a variety of phase structures and semicrystalline morphologies. Crystallization at 145 °C reveals that both α and β crystalline phases of PVDF are present in PVDF/PDMS‐b‐PMMA‐b‐PS blends. Incorporation of the triblock copolymer decreases the degree of crystallization and enhances the proportion of β to α phase of semicrystalline PVDF. Introduction of PDMS‐b‐PMMA‐b‐PS triblock copolymer to PVDF makes the crystalline structures compact and confines the crystal size. Moreover, small‐angle X‐ray scattering results indicate that the immiscible PDMS as a soft block and PS as a hard block are localized in PVDF crystalline structures. © 2019 Society of Chemical Industry     

Thermally Resistive Electrospun Composite Membranes for Low‐Grade Thermal Energy Harvesting

In this work, thermally insulating composite mats of poly(vinylidene fluoride) (PVDF) and polyacrylonitrile (PAN) blends are used as the separator membranes. The membranes improve the thermal‐to‐electrical energy conversion efficiency of a thermally driven electrochemical cell (i.e., thermocell) up to 95%. The justification of the improved performance is an intricate relationship between the porosity, electrolyte uptake, electrolyte uptake rate of the electrospun fibrous mat, and the actual temperature gradient at the electrode surface. When the porosity is too high (87%) in PAN membranes, the electrolyte uptake and electrolyte uptake rate are significantly high as 950% and 0.53 µL s^?1, respectively. In such a case, the convective heat flow within the cell is high and the power density is limited to 32.7 mW m^?2. When the porosity is lesser (up to 81%) in PVDF membranes, the electrolyte uptake and uptake rate are relatively low as 434% and 0.13 µL s^?1, respectively. In this case, the convective flow shall be low, however, the maximum power density of 63.5 mW m^?2 is obtained with PVDF/PAN composites as the aforementioned parameters are optimized. Furthermore, multilayered membrane structures are also investigated for which a bilayered architecture produces highest power density of 102.7 mW m^?2.     

Influences of the chain structure of PE‐b‐PEG on the properties of PE/PE‐b‐PEG blend membranes prepared by TIPS

In this article, a series of diblock copolymer polyethylene‐b‐ poly(ethylene glycol)s (PE‐b‐PEGs) with various molecular weight of polyethylene segment was blended with linear low‐density PE. The PE/PE‐b‐PEG blend porous membranes with high porosity were obtained by thermally induced phase separation (TIPS) process. The isothermal crystallization kinetics of PE/LP/PE‐b‐PEG blends indicated that the introduction of PE‐b‐PEG could inhibit the growth rate of polyethylene crystals which could increase the pore size and porosity of the membranes. The PE/PE‐b‐PEG blend membranes with PE₁₃₀₀‐b‐PEG₂₂₀₀ showed the largest pore size and porosity due to its crystallization behavior during TIPS. The surface of the membranes became smoother and the morphology of the membranes could be effectively tuned by introducing PE‐b‐PEG. Compared with the PE membrane, the PE/PE‐b‐PEG blend membranes exhibited higher hydrophilicity (the water contact angle decreased from 112° to 84°), water permeability (the permeation flux increased from 80 to 440 L/m² h under 0.1 MPa), rejection performance (completely reject carbon particles in the filtration of carbon ink solution), and fouling resistance (the value of protein adsorption dropped from 0.25 to 0.05 mg/cm²). The hydrophilicity and fouling resistance of PE/PE‐b‐PEG blend membranes increased as the length of PE segment in PE‐b‐PEGs decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46499.     

Electrospun Bead‐On‐String Hierarchical Fibers for Fog Harvesting Application

Quest for efficient fog harvesting methods has drawn immense attention in recent times. In this study, electrospinning is used to fabricate three different sets of membranes that are based on pristine poly(N‐isopropylacrylamide) (PNIPAM) fibers, pristine polyvinylidene fluoride (PVDF) fibers, and PNIPAM‐PVDF bead‐on‐string fibers. The wettability of these membranes is investigated as a function of temperature and the effect of their wettability on the fog collection efficiency is determined. Membranes based on pristine PNIPAM and pristine PVDF fibers are fabricated using conventional electrospinning and are shown to have a smooth surface morphology. On the other hand, PNIPAM‐PVDF bead‐on‐string fibers are fabricated using core–shell electrospinning. Water collection efficiency of the membranes is compared to investigate the influence of microstructures and wettability gradient on fog harvesting ability of the samples. Among the three samples, the bead‐on‐string hierarchical fibrous membrane demonstrates the highest fog harvesting rate of 1150 ± 28 mg cm⁻² h⁻¹ at 25 °C and 909 ± 31 mg cm⁻² h⁻¹ at 40 °C. Furthermore, the results demonstrate that the presence of microstructures on the nanofibers improve the fog harvesting efficiency of PNIPAM‐PVDF bead‐on‐string fibers.