Superhydrophilic In-Situ-Cross-Linked Zwitterionic Polyelectrolyte

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Superhydrophilic in situ-Cross-Linked Zwitterionic Polyelectrolyte/PVDFBlend Membrane for Highly Efficient Oil/Water Emulsion Separation Yuzhang Zhu, Wei Xie, Feng Zhang, Tieling Xing, and Jian Jin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b15682 • Publication Date (Web): 01 Mar 2017 Downloaded from http://pubs.acs.org on March 8, 2017

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ACS Applied Materials & Interfaces

Superhydrophilic in situ-Cross-Linked Zwitterionic Polyelectrolyte/PVDF-Blend Membrane for Highly Efficient Oil/Water Emulsion Separation Yuzhang Zhu† , Wei Xie‡, Feng Zhang†, Tieling Xing‡, Jian Jin*,† †

CAS Key Laboratory of Nano-Bio Interface and i-Lab, Suzhou Institute of Nano-Tech and

Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China ‡

College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China

KEYWORDS: oil/water separation, superhydrophilic membrane, zwitterionic polymer, membrane blending, antifouling surface

ACS Paragon Plus Environment

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ABSTRACT: Due to weak hydrophilicity, membranes always experience fouling problems during separations. This phenomenon seriously impedes the development of membrane technologies for practical industrial-oil wastewater treatment. In this work, we successfully fabricated a superhydrophilic zwitterionic poly(vinylidene fluoride) (PVDF) membrane using a two-part process with an in situ cross-linking reaction during non-solvent-induced phase separation and a subsequent sulfonation reaction. To prepare this zwitterionic PVDF membrane, a copolymer poly(dimethylaminoethyl methacrylate-co-2-hydroxyethyl methacrylate) (PDH) was synthesized as a zwitterionic polymer precursor and used as an additive in membrane preparation. This zwitterionic additive is well-immobilized in the membrane using in situ crosslinking to ensure the long-term stability of the membrane, and subsequent sulfonation transforms the precursor to a zwitterionic polymer to produce a superhydrophilic membrane. This superhydrophilic zwitterionic PVDF membrane exhibits high water permeation flux and good antifouling properties for separating oil-in-water emulsions with high separation efficiency.

1. Introduction Membrane technology is acknowledged as one of the most efficient ways to handle a variety of wastewaters, due to its low energy and time consumption, low footprint, high separation efficiency and simple operation.1-3 Recently, many studies have described treatment of

oil-contaminated

wastewater

using

superhydrophilic-underwater

superoleophobic

membranes.4-17 Due to the distinct opposite affinities to oil and water, these membranes exhibit ultrahigh selectivity for oil/water separation, as well as excellent antifouling performance. So far, two main types of superhydrophilic-underwater superoleophobic membranes, metallic mesh or textiles/fabrics and polymeric membranes, have been designed for high-efficiency oil/water


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separation.13 In general, surface functional coating, such as hydrogel,4, 10 scaly titanium oxide,18 fluorodecyl POSS + x-PEGDA,5 Cu(OH)2 nanowire,9 CaCO38 and zwitterionic polyelectrolyte,19, 20

combined with hierarchical structure are always required to fabricate superhydrophilic-

underwater superoleophobic metallic mesh or textiles/fabrics and polymeric membranes. Metallic mesh or textiles/fabrics based superhydrophilic membrane with pore size approximately several microns can effectively remove the free oil from water with ultrahigh permeating flux driven only by self-gravity. However, it is useless to handling emulsified oil-in-water emulsion, in which the oil droplets size is smaller than 20 micron. It notes that a large amount of emulsified oily wastewater are produced in practical industries. Therefore, superhydrophilic-underwater superoleophobic polymeric membranes with pore size smaller than the oil droplet size are demanded to handle these emulsified oil-in-water emulsion. To date, superhydrophilic polymeric membrane are mainly fabricated by surface modification，which is usually implemented via surface coating and surface grafting. As typical examples, zwitterionic polelectrolyte grafted PVDF membrane,21 mineral-coated polypropylene membranes,8, 22 surface-coating of a crosslinked hydrogel23 on the surface of PVDF membrane and x-PEGDA6 coated nanofibrous membrane were prepared and exhibited excellent separation performance for emulsified oil-inwater emulsion. However, surface grafting and surface coating always suffer time consumption, requirement of harsh chemical environment, and instability of coated layer, which greatly impede the development of superhydrophilic polymeric membrane in practical industry. Thus, developing a robust and simple strategy to design superhydrohilic polymeric membrane are greatly demanded. Besides, blending modification which blend hydrophilic additives directly into membrane matrix during membrane preparation has been proved to be an effective strategy and frequently


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used to produce hydrophilic polymeric membranes due to its single operation process and easy for scale up and mass production.24-30 So far, three main types of hydrophilic additives including hydrophilic polymers, amphiphilic copolymers, and inorganic particles are often used.31-33 Among the three types of additives, hydrophilic and amphiphilic polymers possess the best affinity to water, but exhibit weak compatibility with with polymer matrix, such as PVDF, polysulfone (PSf), and polyacrylonitrile (PAN). Therefore, the content of hydrophilic polymers in the membrane is limited and give rise to insufficient hydrophilicity. In addition, the blended hydrophilic polymers are easy to release from the membrane during long-term filtration. It will cause the attenuation of membrane hydrophilicity gradually. Although the hydrophilicity of membranes could be improved by blending hydrophilic nanoparticles, improvements to hydrophilicity are still limited. As for inorganic nanoparticles, the uniform dispersion in membrane matrix is crucial for blending modification. Aggregation occurs since the amount of nanoparticles is high, which is disadvantage for the improvement of hydrophilicity. As for oil/water separation, stable hydrated layer is required to impede the oil droplet contacting the surface of membrane matrix and give the membrane high separation efficiency, as well as antifouling performance stability. However, few additives can endow the membranes with superhydrophilicity. It is well known that sulfobetaine zwitterionic polyelectrolyte contains both anionic and cationic species in the polymer side chain. Due to the strong interaction between ions and water, a stable hydrated layer can be formed around this polymer chain, effectively preventing foulants, such as protein, marine organisms, and oil droplets, from attaching. Therefore, zwitterionic polyelectrolytes have been widely used for designing materials with improved anti-fouling performance.34-38 In our previous work, we demonstrated that a zwitterionic polyelectrolyte-


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grafted PVDF membrane prepared via atom transfer radical polymerization (ATRP) exhibited superhydrophilic-underwater superoleophobic property and superior antifouling properties for separating oil-in-water emulsions.21 However, oxygen-free environment is always requested for ATRP process, which severely impede the development of it for producing the membranes with large scale and large quantities. Developing a relatively simple strategy to fabricate zwitterionic polymer functionalized membranes for oil/water separation is thus highly required. In this work, a zwitterionic polymer was used as a hydrophilic additive to blend into the PVDF membrane. The zwitterionic polymer-blended PVDF membrane was fabricated by an in situ cross-linking during non-solvent phase separation (NIPS) and a subsequent sulfonation reaction, as shown in Scheme 1. The in situ cross-linking reaction effectively solves the issue of poor compatibility between the zwitterionic polymer and PVDF matrix. The zwitterionic polymer in the membrane is subsequently transformed into a zwitterionic polyelectrolyte through sulfonation to give a superhydrophilic zwitterionic polyelectrolyte/PVDF-blend membrane. Since it is cross-linked to the blend membrane, the zwitterionic polyelectrolyte is immobilized and releases from the membrane much less, ensuring long-term stability. As a result, the superhydrophilic zwitterionic polyelectrolyte/PVDF-blend membrane shows excellent performance in the separation of oil-inwater emulsions with high flux and high rejection (residual oil content in the filtrate is as low as 1.2 ppm after one filtration). Moreover, the membrane exhibits improved oil-fouling, with a lower flux decline with respect to permeation volume and high water flux recovery up to 98%.

2. Experimental Section 2.1 Materials PVDF powder (Solef1015, Mn=238,000) was purchased from the Solvay Chemicals Company and used as received. 2-(dimethylamino)ethyl methacrylate (DMAEMA) and


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hydroxyethyl methacrylate (HEMA) were purchased from TCI. These monomers were passed through a basic alumina column to remove the inhibitor and stored at -20°C before use. Potassium persulfate, sodium thiosulfate, glutaric dialdehyde (25wt% in aqueous solution), concentrated H2SO4 and N-methyl-2-pyrrolidinone (NMP, 99%) were all purchased from Sinopharm Reagent Co. Ltd. (Shanghai, China) and used as received. 1,3-propanesultone was purchased from J&K (Beijing, China). 2.2 Synthesis of copolymer poly(dimethylaminoethyl methacrylate-co-2-hydroxyethyl methacrylate) poly (DMAEMA-r-HEMA) The copolymer poly (DMAEMA-r-HEMA) (PDH) was synthesized by radical polymerization. The detailed procedure was as follows: 6 ml DMAEMA and 4 ml HEMA were added to 100 ml solvent composed of a 1:1 v/v mixture of water and ethanol. After bubbling with N2 for 30 min at room temperature, 0.05 g NaHSO3 and 0.05 g K2S2O8 was added and the solution was left at 40°C to polymerize for 12 h. The solution was exposed to air at room temperature to terminate the polymerization reaction. The solvent was removed under vacuum to give a viscous mixture, which was resolved with water and purified by dialysis (MD34, molecular weight cut-off: 3500 Da) to remove residual monomer. The copolymer PDH was obtained by evaporating the water under vacuum with the azeotropic aid of ethanol. The chemical composition of PDH was determined by 1H NMR (Figure 1). The molar ratio of the DMAEMA in the PDH copolymer was calculated from the 1H NMR spectrum by comparing the overall integration of the 3.6-4.4 ppm region, which is ascribed to the 4 protons of the two methylene groups in the side chain of HEMA (d and f) and the two protons of the sidechain methylene groups of DMAEMA (d), to the overall integration of the 2.2-3.0 ppm region, which represents eight protons from two methyl groups (c) and one methylene group (e) that are linked


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to N atoms in DMAEMA.39,

40

By this calculation, the molar ratio of DMAEMA in the

copolymer PDH is 53%.

Figure 1. 1H NMR spectrum of synthesized PDH copolymer in CDCl3. (a-f) Proton peaks of signed groups corresponding to the inserted molecular structure. 2.3 Membrane preparation First, 2 g PVDF powder, 2 g PDH and 1.6 ml water were added to 20 ml NMP and the solution was stirred at 70 °C for 12 h. The solution was left at 70 °C to eliminate bubbles. The solution was spread onto a flat glass plate using a casting knife with a gate height of 300 µm and immersed in a water coagulation bath immediately. The water coagulation bath was composed of 1 wt% glutaric dialdehyde and 0.3 wt% concentrated H2SO4. After 1 h, the membrane was removed from the coagulation bath and placed into pure water to complete the phase separation and yield the cross-linked PVDF/PDH-blend membrane. To prepare the PVDF/PSH-blend membrane, the prepared cross-linked PVDF/PDH-blend membrane was allowed to dry and was then immersed in THF containing 10 mg/ml 1,3-propane sultone for 48 h at 40 °C to allow


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sulfonation to occur. During this process, PDH was transformed to the zwitterionic copolymer poly(3-(N-2-methacryloxyethyl-N,N-dimethyl)

ammonatopropanesultone)-co-2-hydroxyethyl

methacrylate) (PSH) and a PVDF/PSH-blend membrane was finally obtained. The obtained PVDF/PSH-blend membrane was thoroughly washed with ethanol and water and stored in water before use. For the preparation of the PVDF/PDH-blend membrane without cross-linking, the same procedure was used but without the addition of glutaric dialdehyde in the coagulation bath. 2.4 Characterization Water contact angle and underwater oil contact angle were characterized using an OCA20 instrument (Data-Physics, Germany) at ambient temperature. A 2-µl water droplet and 5µl 1,2-dichloroethane droplet, respectively, were used in the experiment. To determine the content of PDH in the cross-linked PVDF/PDH-blend membrane and PVDF/PDH-blend membrane without cross-linking, thermogravimetric analysis (TG, Seiko Exstar 6000, Japan) was conducted under nitrogen with a heating rate of 10 °C min-1. X-ray photoelectron spectroscopy (XPS) was detected on a Thermo ESCALAB 250 XI multifunctional imaging electron spectrometer. The morphology of the membranes was characterized on a cold-fieldemission scanning electron microscope (Hitachi S4800, Japan). Attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) was detected on a Nicolet 6700 (Thermo Fisher, America). 2.5 Membrane performance test Membrane performance for oil/water separation was performed on a lab-scale cross-flow filtration system. Prepared membranes were fixed onto a circular cell with an effective surface area of 7.1 cm2. Before the test, the membrane was compacted with pure water at 1.6 bar until the flux was stable. Hydraulic pressure was localized at 0.6 bar with a velocity approximately 30


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LPH. Water permeability was measured first. To evaluate membrane performance in oil-in-water emulsion separation, 20 ml isooctane was added to 2000 ml pure water to form an oil-in-water emulsion under high-shear stirring for 30 min. The emulsion was allowed to permeate through the membrane. The change in permeating flux with time was monitored by electronic balance. The flux variation with permeation volume was calculated using the following equation: J=

∆V Aeff ∆t

where ∆V is the permeation volume of filtrate that passed through the membrane in a predetermined time ∆t; Aeff is the effective filtration area. The filtrate was collected during the filtration and the oil content of the filtrate and feed solution were determined on an Auraro 1030w O-I-Analytical total organic carbon analyser (TOC) to calculate the separation efficiency. To evaluate the pure water permeability recovery ratio, hydraulic washing was conducted at a cross-flow velocity 70 LPH for 1 h after one filtration to recover the water permeation. The pure water permeation was measured again at 0.6 bar and a velocity of 30 LPH.

3. Results and Discussion 3.1 Preparation and characterization of blend membranes The PVDF/PSH-blend membrane was prepared via a combined process of in situ crosslinking of hydrophilic additive copolymer PDH during phase separation and subsequent sulfonation. As schematically illustrated in Scheme 1, the PVDF casting solution blended with PDH was cast onto the glass plate and immersed into the coagulation bath composed of glutaric dialdehyde and H2SO4. Due to the hydrophilicity of the PDH copolymer, PDH in the casting solution of PVDF tends to migrate to the membrane surface during phase separation driven by surface segregation.41-44 Moreover, the acid in the coagulation bath ionizes the tertiary amine


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group in the side chain of DMAEMA in PDH, which further improves the hydrophilicity of PDH and enhances surface segregation. The presence of glutaric dialdehyde in the water coagulation bath acted as a cross-linker that reacted with hydroxyl groups in the side chain of the PHEMA segment of PDH, immobilizing PDH on the PVDF membrane. As the PVDF/PDH-blend membrane was formed, sulfonation of the PVDF/PDH-blend membrane was carried out to transform the tertiary amine group to a zwitterionic group in the PDMAEMA side chain of PDH to further improve membrane hydrophilicity.

Scheme 1. Schematic description of phase separation in the formation of zwitterionic PVDF/PSH-blend membranes using random PDH copolymer as an additive, combined with in situ cross-linking and subsequent sulfonation.


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Figure 2. ATR-FTIR spectra of pristine PVDF membrane (blue), PVDF/PDH-blend membrane without crosslinking (green), cross-linked PVDF/PDH-blend membrane (black), and zwitterionic PVDF/PSH-blend membrane (red).

ATR-FTIR spectroscopy was used to determine the surface chemistry of the membranes. Figure 2 shows four curves ascribed to pristine PVDF membrane (blue line), PVDF/PDH-blend membrane without cross-linking (green line), cross-linked PVDF/PDH-blend membrane (black line) and zwitterionic PVDF/PSH-blend membrane, respectively. Three strong characteristic peaks at 1398 cm-1, 1174 cm-1 and 879 cm-1, ascribed to -CH2- in plane blending, -CF2stretching, and skeletal vibration of PVDF C-C bonds, respectively, are observed in all spectra.45,46 Two new peaks at 3398 cm-1 and 1728 cm-1, assigned to the stretching vibration of the hydroxyl group (-OH) and carbonyl group (C=O), respectively, appear in the spectra of blend membranes.47,48 These peaks are derived from PDH. After sulfonation, two peaks at 1161 cm-1 and 1040 cm-1 are observed in the curve for the zwitterionic PVDF/PSH-blend membrane. These peaks are ascribed to asymmetric and symmetric stretching of S=O in -SO3 groups,


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respectively.49,50 This result demonstrates that the zwitterionic component has been successfully introduced into the membrane.

Figure 3. TGA curves of pristine PVDF membrane (black line), PVDF/PDH-blend membrane without cross-linking (red line), and cross-linked PVDF/PDH-blend membrane (blue line).

TG analysis was performed to evaluate the weight loss of PVDF/PDH with and without cross-linking. As shown in Figure 3, pristine PVDF membranes exhibit a sharp weight-loss stage below 500°C. In comparison, the PVDF/PDH-blend membrane without cross-linking shows two obvious weight-loss stages. The first stage is ~ 8 wt% in the range of 150°C to 330°C, which is attributed to the decomposition of the side chain of HMEA in PDH.51 According to the molar ratio of DMAEMA in PDH (~ 53%) as calculated previously, the PDH content in the PVDF/PDH-blend membrane without cross-linking is ~ 27wt% (details of calculation are shown in Supporting Information). The second stage of weight loss in the range of 330°C to 550°C constitutes a loss of ~ 48wt%. This is attributed to the decomposition of DMAEMA in the


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copolymer PDH and PVDF matrix.52-53 As the temperature increases to 700°C, a residual weight loss of ~ 29wt% is obtained, which is ascribed to carbon produced from the decomposition of PDH and PVDF under N2 atmosphere. For the cross-linked PVDF/PDH-blend membrane, there is a ~ 4% weight loss below 270°C, which is attributed to the degradation of HEMA in PDH without cross-linking. The residual component in the membrane gives a weight loss of ~ 50% in the range of 270°C - 550°C. As the temperature rises to 700°C, the weight loss of residual carbon is ~ 30 wt%. Comparing the residual weight of carbon in the PVDF/PDH-blend membranes with and without cross-linking, it is evident that the membranes have similar PDH content. Therefore, approximately half content of HEMA are cross-linking based on calculation. XPS spectra was performed to detect the surface composition of as-prepared blend membranes and the results is shown in Figure 4. The detailed analysis and calculation results of the surface segregation ratios obtained on the XPS wide scan survey and C1s spectra have been listed in Table 1. As observed from Figure 4a, four elements, C, F, N, O, are detected in the XPS survey spectra of the PVDF/PDH-blend membrane without cross-linking and cross-linked PVDF/PDH-blend membrane. After sulfonation, two peaks ascribed to S1s and S2p, respectively, are clearly observed in the zwitterionic PVDF/PSH-blend membrane. The atomic content of the five elements are calculated based on the peak area of the elements in consideration of sensitivity factor. As shown in Table 1, the atomic contents of F and N in the PVDF/PDH-blend membrane without cross-linking and cross-linked PVDF/PDH-blend membrane are 29.8% and 29%, and 2.6% and 2.9%, respectively. It means that the surface fraction of the hydrophilic copolymer in the cross-linked PVDF/PDH-blend membrane is higher than in the PVDF/PDH-blend membrane without cross-linking. The atomic contents of S and N in zwitterionic PVDF/PSH-blend membrane is 2.0% and 2.2%. In consideration of the


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stoichiometric ratio of N/S in sulfobetaine zwitterionic polyelectrolyte is 1. It means that ~90% (e.g 2.0/2.2) polyDMAEMA has been sulfonated.

Figure 4. X-ray photoelectron spectroscopy spectra of the as-prepared membranes. a) Wide scan survey and b-d) C1s spectra of PVDF/PDH-blend membrane without cross-linking, cross-linked PVDF/PDH-blend membrane, and zwitterionic PVDF/PSH-blend membrane.

The C1s spectra of the three membranes are shown in Figure 4b-d. Five peaks centred at 290.4 eV ascribed to CF2, 285.9 eV ascribed to CH2 of PVDF, and 288.8 eV ascribed to O-C=O, 286.3 eV ascribed to C-N/C-O, and 284.8 eV ascribed to CH of hydrophilic copolymer additive


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are obtained.44, 54According to the chemical structure of PVDF and hydrophilic copolymer PDH or zwitterionic polymer, the near-surface molar ratio of hydrophilic copolymer, φ, could be obtained using the following expression: φ=

AሺO-C=Oሻ AሺO-C=Oሻ +AሺCF2 ሻ

where A(O-C=O) is the molar ratio of O-C=O in PHD or zwitterionic polymer, A(CF2) is the molar ratio of CF2 in PVDF. The calculated φ are 20.3%, 23.5%, and 20.8% corresponding to PVDF/PDH-blend membrane without cross-linking, cross-linked PVDF/PDH membrane and zwitterionic PVDF/PSH-blend membrane. It shows that the surface segregation ratio of zwitterionic polymer in the zwitterionic PVDF/PSH-blend membrane is less than in the crosslinked PVDF/PDH membrane. We think that a small amount of non-cross-linked PDH are released from the membrane during the process of sulfonation reaction. Table 1 Surface elemental compositions of as-prepared membranes. Atomic percentage of surface element (%) C

F

N

O

S

Surface segregation ratio (φ, %)

PVDF/PDH without crosslinking

57.5

29.8

2.6

10.1

0

20.3

Cross-linked PVDF/PDH

56.4

29

2.9

11.7

0

23.5

PVDF/PSH

55.9

26.4

2.2

13.4

2.0

20.8

Membrane

The morphologies of the prepared membranes were characterized using SEM. As shown in Figure 5a, a pristine PVDF membrane exhibits a dense, rough surface with a limited amount of pores in the range of 20-40 nm. In the PVDF/PDH-blend membranes, the PDH additive is expected to be released from the membrane during phase separation. As discussed above, the PDH content in these membranes is ~27 wt%, meaning that ~23 wt% PDH is released from the


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membranes. This released PDH may act as a pore-forming agent to improve the porosity of PVDF membranes. As a result, additional pores are observed in the top-view SEM images of PVDF/PDH-blend membranes without cross-linking and cross-linked PVDF/PDH-blend membranes (Figure 5b and 5c). The pore size of PVDF/PDH-blend membranes without crosslinking is much larger than that of the cross-linked membranes. This is due to the weak compatibility between PDH and PVDF, which give rise to significant phase segregation that leads to larger pores. In contrast, the in situ cross-linking reaction can effectively impede this phase segregation, and relatively small pores are thus observed. The PVDF/PSH-blend membrane surface is much rougher than the cross-linked version (Figure 5d). We propose that this is due to swelling of PSH on the membrane surface, since membrane hydrophilicity is greatly improved by sulfonation.

Figure 5. Top-view SEM images of a) pristine PVDF membrane, b) PVDF/PDH-blend membrane without cross-linking, c) cross-linked PVDF/PDH-blend membrane, and d) zwitterionic PVDF/PSH-blend membrane.


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Figure 6. Tensile strength of pure PVDF membrane (), PVDF/PDH-blend membrane without cross-linking (), cross-linked PVDF/PDH-blend membrane () and zwitterionic PVDF/PSHblend membrane ().

The mechanical strength of the membranes was also evaluated by measuring the tensile strength with respect to strain. As observed from Figure 6, the pure PVDF membrane showed the highest tensile strength (~1.54 MPa) with an elongation of 57%. In comparison, the tensile strength of the PVDF-blend membranes decreased significantly after introducing PDH into the PVDF matrix. As shown in Figure 6, PVDF/PDH-blend membranes without cross-linking display a tensile strength of 0.52 MPa, with 13% elongation. The tensile strength of cross-linked PVDF/PDH membranes increased 0.6 MPa, with a corresponding elongation of 20%, which demonstrates that in situ cross-linking positively affects mechanical strength. Sulfonation has little effect on tensile strength: the PVDF/PSH-blend membrane exhibited a tensile strength of 0.59 MPa, with elongation of 24%. We hypothesize that decreased tensile strength and strain is due increased porosity and pore size.


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3.2 Surface wettability

Figure 7. a) Variation of water CA over time and b) corresponding underwater oil CA on the surfaces of pure PVDF membrane, PVDF/PDH-blend membrane without cross-linking, crosslinked PVDF/PDH-blend membrane, and zwitterionic PVDF/PSH-blend membrane.

The surface wettability of the membranes was characterized by measuring the change in water contact angle over time (Figure7). The water CA of the pure PVDF membrane was ~ 82° and decreased to 65° after 120 s (Figure 7a). The PVDF/PDH-blend membrane without crosslinking exhibited an initial water CA of ~81° and decreased to 0° after 120 s. The initial water CA of cross-linked PVDF/PDH-blend membrane was ~75°, which is somewhat lower than the


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PVDF/PDH-blend membrane without cross-linking. However, the time for water droplet permeation into the cross-linked PVDF/PDH-blend membrane is just 20 s, which is much shorter than that of PVDF/PDH-blend membrane without cross-linking. This result demonstrates that the hydrophilicity of the membrane is improved after cross-linking. The introduction of sulfonate groups further improves the hydrophilicity of the blend membrane. The initial water CA of the zwitterionic PVDF/PSH-blend membrane is ~ 61° and the time for water droplet permeation into the membrane is only 10 s. The underwater oil CA of the pure PVDF membrane was ~ 134° (Figure 7b), and decreased to zero after several minutes due to the inherent oleophilic property of PVDF. Angles for the PVDF/PDH-blend membrane with and without cross-linking were 147° and 145°, respectively. Both membranes exhibit similar underwater oleophobic properties. In comparison with PVDF/PDH-blend membranes with and without cross-linking, the zwitterionic PVDF/PSH-blend membrane exhibits underwater superhydrophilicity, with an underwater oil CA of ~156°. As the zwitterionic group has higher surface tension, it can enhance the interaction between water and polymer chains, and a thicker hydrated layer is thus formed on the membrane surface. Dynamic underwater oil-adhesion measurement are conducted to evaluate the underwater oil-adhesion force and the result is shown in Figure 8. As for the PVDF/PDH-blend membranes with and without cross-linking, obvious stretches are observed when the oil droplet preloaded and then lifted from their surfaces. It demonstrates a high oil-adhesion. The high oil-adhesion force is ascribed to the weaker hydrophilic property of the two membranes. Additionally, the tertiary amine groups in polyDMAEMA endow the blend membranes with positive charges, which give rise to the membrane with higher oil-adhesion force according to Lin’s research.55 In comparison, as for zwitterionic PVDF/PSH-blend membrane, the oil droplet could be totally


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lifted off from the surface due to its relatively higher hydrophilic property. It indicates that zwitterionic PVDF/PSH blend membrane possess a low oil-adhesion force, which would endow the membrane with excellent antifouling performance as separating the oil-in-water emulsion.

Figure 8 Dynamic photographs of underwater oil-adhesion behavior on the surface of a) PVDF/PDH without cross-linking, b) cross-linked PVDF/PDH-blend membrane, and c) zwitterionic PVDF/PSH-blend membrane. The volume of the oil droplets is 5 µl.

3.3 Membrane performance for separating oil-in-water emulsions The permeation flux of isooctane-in-water emulsions was first tested to examine membrane performance. As shown in Figure 9a, the PVDF/PDH-blend membrane without crosslinking gives an initial permeating flux of 2600 Lm-2h-1bar-1 when isooctane-in-water emulsion permeates the membrane. The permeation flux declines quickly with respect to the permeation volume (Figure 9b). When the permeation volume is 137 ml, permeating flux is only ~ 12% of the initial value; in contrast, initial permeating fluxes of 3850 Lm-2h-1bar-1 and 6350 Lm-2h-1bar-1 were obtained for cross-linked PVDF/PDH-blend and zwitterionic PVDF/PSH-blend


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membranes, respectively. The flux decrease for these two membranes is slower than for PVDF/PDH-blend membranes without cross-linking. The residual flux of cross-linked PVDF/PDH-blend membranes is ~ 26% when the permeation volume is at or below 440 ml. The flux decrease of the zwitterionic PVDF/PSH-blend membrane is much slower than for the crosslinked PVDF/PDH-blend membrane. The residual flux is ~ 36% of the initial flux for permeation volumes, surpassing 950 ml by the end of filtration experiment. This indicates that the introduction of zwitterionic groups greatly improves antifouling performance. It is worthy noted that there is a stable permeating flux with respect to the permeating volume at the end of plots of PVDF/PSH-blend membrane. We propose that this stable limited permeating flux is ascribed to the coalescing and floating of oil droplets at the surface of membranes, which finally induces the demulsification of the feed solution (Scheme 2).

Figure 9. a) Initial permeation flux and b) respective flux decline behavior of PVDF/PDH-blend membrane without cross-linking, cross-linked PVDF/PDH-blend membrane, and zwitterionic PVDF/PSH-blend membrane, with respect to permeation volume during separation of an isooctane-in-water emulsion.


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Scheme 2 Schematic illustration of the process of demulsification during the separation process of oil-in-water emulsion by zwtterionic PVDF/PSH blend membrane.

To evaluate antifouling properties, water-permeation flux recovery was examined using pure water as a feed solution to recover the flux of the membranes after permeation of a certain volume of isooctane-in-water emulsion. As shown in Figure 10, the water-permeation flux recoveries of the PVDF/PDH-blend membrane without cross-linking, the cross-linked PVDF/PDH-blend membrane, and the zwitterionic PVDF/PSH-blend membrane are 40%, 71%, and 98%, respectively. This result demonstrates that the zwitterionic PVDF/PSH-blend membrane possesses the best fouling recovery performance and exhibits superior antifouling performance for oil-in-water emulsion separation, thanks to the excellent hydrophilicity of PSH. The antifouling performance stability of zwitterionic PVDF/PSH-blend membrane are also performed by long-term continuous filtration experiment and the result is shown in Figure 11. It shows that the permeating flux of the zwitterionic PVDF/PSH-blend membrane is gradually decreased to ~10% of the initiated flux after 10 h continuous filtration experiment when using surfactant-free isooctane-in-water emulsion as feed. After simply hydraulic washing, the


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recovery of permeating flux is as high as ~91%. It indicates that the membrane has good stability of antifouling performance for long-term filtration process.

Figure 10. Permeation flux recovery of PVDF/PDH-blend membranes without cross-linking, cross-linked PVDF/PDH-blend membranes, and zwitterionic PVDF/PSH-blend membranes.

Figure 11. Permeating flux decline behavior of zwitterionic PVDF/PSH-blend membrane during long-term continuous filtration experiment where isooctant-in-water emulsion is used as feed solution. The applied pressure during filtration process is 0.6 bar.


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Separation efficiency was examined by measuring the oil content in the collected filtrate. As shown in Figure 12a, numerous oil droplets with droplet size of 4~40 µm in the feed isooctane-in-water emulsion could be clearly observed using optical microscopy. In contrast, almost no oil droplets could be observed in the transparent collected filtrate. As measured by TOC, the oil content in the filtrate was 2.4 ppm for the PVDF/PDH-blend membrane without cross-linking, 1.4 ppm for the cross-linked PVDF/PDH-blend membrane, and 1.2 ppm for the zwitterionic PVDF/PSH-blend membrane, respectively (Figure 12b).

Figure 12. a) Photograph and micrographs of feed and filtrate after permeation through PVDF/PSH-blend membrane and b) Oil content of collected filtrates after permeation through the membranes.

4. Conclusions A zwitterionic PVDF/PSH-blend membrane with superhydrophilic and underwater superoleophobic properties has been successfully fabricated by NIPS combined with in situ cross-linking and a subsequent sulfonation reaction. During the phase separation the in situ


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cross-linking reaction can effectively improve the hydrophilicity and porosity of the blend membrane. The introduction of zwitterionic sulfonate groups can further improve the hydrophilicity of the membrane, imparting superwetting behavior and endowing the membrane with remarkable antifouling properties for separating oil-in-water emulsions. The recovery of water flux after filtration experiment by the PVDF/PSH-blend membrane is as high as 98%, demonstrating superior antifouling performance, when separating oil-in-water emulsions. Additionally, the high recovery (~91%) of flux for separating oil-in-water emulsion after longterm continuous filtration experiment indicates the good stability of antifouling performance. With increased demand for oily wastewater treatment, our work provides an alternative strategy to produce superhydrophilic membranes for highly efficient oil/water separation.

ASSOCIATED CONTENT Supporting Information. Supporting Information Available: The related chemical reactions for fabricating zwitterionic PVDF/PSH-blend membrane; The detail calculation of PDH content in PVDF blend membrane. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

ORCID


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Yuzhang Zhu: 0000-0002-7279-2903 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Key Project of National Natural Science Foundation of China (21433012), the China Postdoctoral Science Foundation (2015M590511), the National Natural Science Foundation of China (51625306, 51603229, 21406258), the Natural Science Foundation of Jiangsu Province (BE2015072, BK20140384, BK20140385), and the Key Laboratory of Adsorption and Separation Materials and Technologies of Zhejiang Province (No. XFFL2015). REFERENCES (1) Nicolaisen, B. Developments in Membrane Technology for Water Treatment. Desalination 2003, 153, 355-360. (2) Baker, R. W. Membrane Technology and Application, 3rd ed.; Wiley: Hoboken, 2012. (3) Peters, T. Membrane Technology for Water Treatment. Chem. Eng. Technol. 2010, 33, 1233-1240. (4) Gao, S.; Sun, J.; Liu, P.; Zhang, F.; Zhang, W.; Yuan, S.; Li, J.; Jin, J. A Robust Polyionized Hydrogel with an Unprecedented Underwater Anti-Crude-Oil-Adhesion Property. Adv. Mater. 2016, 28, 5307-5314. (5) Kota, A. K.; Kwon, G.; Choi, W.; Mabry, J. M.; Tuteja, A. Hygro-Responsive Membranes for Effective Oil-Water Separation. Nat. Commun. 2012, 3, 1025.


26

Page 27 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Raza, A.; Ding, B.; Zainab, G.; El-Newehy, M.; Al-Deyab, S. S.; Yu, J. In Situ CrossLinked Superwetting Nanofibrous Membranes for Ultrafast Oil–Water Separation. J. Mater. Chem. A 2014, 2, 10137-10145. (7) Tao, M.; Xue, L.; Liu, F.; Jiang, L. An Intelligent Superwetting PVDF Membrane Showing Switchable Transport Performance for Oil/Water Separation. Adv. Mater. 2014, 26, 29432948. (8) Chen, P. C.; Xu, Z. K. Mineral-Coated Polymer Membranes with Superhydrophilicity and Underwater Superoleophobicity for Effective Oil/Water Separation. Sci. Rep. 2013, 3, 2776. (9) Zhang, F.; Zhang, W. B.; Shi, Z.; Wang, D.; Jin, J.; Jiang, L. Nanowire-Haired Inorganic Membranes

with

Superhydrophilicity

and

Underwater

Ultralow

Adhesive

Superoleophobicity for High-Efficiency Oil/Water Separation. Adv. Mater. 2013, 25, 41924198. (10) Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23, 4270-4273. (11) Zhu, Y.; Xie, W.; Li, J.; Xing, T.; Jin, J. pH-Induced Non-Fouling Membrane for Effective Separation of Oil-in-Water Emulsion. J. Membr. Sci. 2015, 477, 131-138. (12) Zhu, Y.; Wang, D.; Jiang, L.; Jin, J. Recent Progress in Developing Advanced Membranes for Emulsified Oil/Water Separation. NPG Asia Mater. 2014, 6, e101. (13) Ma, Q.; Cheng, H.; Fane, A. G.; Wang, R.; Zhang, H. Recent Development of Advanced Materials with Special Wettability for Selective Oil/Water Separation. Small 2016, 12, 2186-2202.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 34

(14) Zhang, W.; Zhu, Y.; Liu, X.; Wang, D.; Li, J.; Jiang, L.; Jin, J. Salt-Induced Fabrication of Superhydrophilic and Underwater Superoleophobic PAA-g-PVDF Membranes for Effective Separation of Oil-in-Water Emulsions. Angew. Chem. Int. Ed. 2014, 53, 856-860. (15) Xue, Z.; Cao, Y.; Liu, N.; Feng, L.; Jiang, L. Special Wettable Materials for Oil/Water Separation. J. Mater. Chem. A 2014, 2, 2445-2460 (16) Padaki, M.; Surya Murali, R.; Abdullah, M. S.; Misdan, N.; Moslehyani, A.; Kassim, M. A.; Hilal, N.; Ismail, A. F. Membrane Technology Enhancement in Oil–Water Separation. A Review. Desalination 2015, 357, 197-207. (17) Wen, Q.; Di, J.; Jiang, L.; Yu, J.; Xu, R. Zeolite-Coated Mesh Film for Efficient Oil–Water Separation. Chem. Sci. 2013, 4, 591-595 (18) Zheng X.; Guo, Z. Y.; Tian D. L.; Zhang, X. F.; Li, W. X.; Jiang L. Underwater SelfCleaning Scaly Fabric Membrane for Oily Water Separation, ACS Appl. Mater. Interfaces, 2015, 7, 4336-4343. (19) Liu, Q.; Patel, A. A.; Liu, L. Superhydrophilic and Underwater Superoleophobic Poly(sulfobetaine methacrylate)-Grafted Glass Fiber Filters for Oil-Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 8996-9003. (20) He, K.; Duan, H.; Chen, G. Y.; Liu, X.; Yang, W.; Wang, D. Cleaning of Oil Fouling with Water Enabled by Zwitterionic Polyelectrolyte Coatings: Overcoming the Imperative Challenge of Oil-Water Separation Membranes. ACS Nano 2015, 9, 9188-9198. (21) Zhu, Y.; Zhang, F.; Wang, D.; Pei, X. F.; Zhang, W.; Jin, J. A Novel Zwitterionic Polyelectrolyte Grafted PVDF Membrane for Thoroughly Separating Oil from Water with Ultrahigh Efficiency. J. Mater. Chem. A 2013, 1, 5758-5765.


28

Page 29 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Yang, H. C.; Pi, J. K.; Liao, K. J.; Huang, H.; Wu, Q. Y.; Huang, X. J.; Xu, Z. K. SilicaDecorated Polypropylene Microfiltration Membranes with a Mussel-Inspired Intermediate Layer for Oil-in-Water Emulsion Separation. ACS Appl. Mater. Interfaces 2014, 6, 1256612572. (23) Yuan, T.; Meng, J.; Hao, T.; Wang, Z.; Zhang, Y. A Scalable Method toward Superhydrophilic and Underwater Superoleophobic PVDF Membranes for Effective Oil/Water Emulsion Separation. ACS Appl. Mater. Interfaces 2015, 7, 14896-14904. (24) Zhao, Y.-H.; Zhu, B.-K.; Kong, L.; Xu, Y.-Y. Improving Hydrophilicity and Protein Resistance of Poly (vinylidene fluoride) Membranes by Blending with Amphiphilic Hyperbranched-Star Polymer. Langmuir 2007, 23, 5779-5786. (25) Chen, Y.; Wei, M.; Wang, Y. Upgrading Polysulfone Ultrafiltration Membranes by Blending with Amphiphilic Block Copolymers: Beyond Surface Segregation. J. Membr. Sci. 2016, 505, 53-60. (26) Liu, F.; Hashim, N. A.; Liu, Y.; Abed, M. R. M.; Li, K. Progress in the Production and Modification of PVDF Membranes. J. Membr. Sci. 2011, 375, 1-27. (27) Kang, G.-d.; Cao, Y.-m. Application and Modification of Poly(vinylidene fluoride) (PVDF) Membranes – A Review. J. Membr. Sci. 2014, 463, 145-165. (28) Mansouri, J.; Harrisson, S.; Chen, V. Strategies for Controlling Biofouling in Membrane Filtration Systems: Challenges and Opportunities. J. Mater. Chem. 2010, 20, 4567. (29) Wang, Y.-Q.; Su, Y.-L.; Ma, X.-L.; Sun, Q.; Jiang, Z.-Y. Pluronic Polymers and Polyethersulfone Blend Membranes with Improved Fouling-Resistant Ability and Ultrafiltration Performance. J. Membr. Sci. 2006, 283, 440-447.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

(30) Yi, Z.; Zhu, L.-P.; Xu, Y.-Y.; Zhao, Y.-F.; Ma, X.-T.; Zhu, B.-K. Polysulfone-Based Amphiphilic Polymer for Hydrophilicity and Fouling-Resistant Modification of Polyethersulfone Membranes. J. Membr. Sci. 2010, 365, 25-33. (31) Asatekin, A.; Mayes, A. M. Oil Industry Wastewater Treatment with Fouling Resistant Membranes Containing Amphiphilic Comb Copolymers. Environ. Sci. Technol. 2009, 43, 4487-4492. (32) Cao, X.; Ma, J.; Shi, X.; Ren, Z. Effect of TiO2 Nanoparticle Size on the Performance of PVDF Membrane. Appl. Surf. Sci. 2006, 253, 2003-2010. (33) Liang, S.; Xiao, K.; Mo, Y.; Huang, X. A novel ZnO Nanoparticle Blended Polyvinylidene Fluoride Membrane for Anti-Irreversible Fouling. J. Membr. Sci. 2012, 394-395, 184-192. (34) Yu, H.; Cao, Y.; Kang, G.; Liu, J.; Li, M.; Yuan, Q. Enhancing Antifouling Property of Polysulfone Ultrafiltration Membrane by Grafting Zwitterionic Copolymer via UV-Initiated Polymerization. J. Membr. Sci. 2009, 342, 6-13. (35) Wan, F.; Pei, X.; Yu, B.; Ye, Q.; Zhou, F.; Xue, Q. Grafting Polymer Brushes on Biomimetic Structural Surfaces for Anti-algae Fouling and Foul Release. ACS Appl. Mater. Interfaces 2012, 4, 4557-4565. (36) Jiang, S.; Cao, Z. Ultralow-Fouling, Functionalizable, and Hydrolyzable Zwitterionic Materials and Their Derivatives for Biological Applications. Adv. Mater. 2010, 22, 920932. (37) Keefe, A. J.; Jiang, S. Poly(zwitterionic)protein Conjugates Offer Increased Stability without Sacrificing Binding Affinity or Bioactivity. Nat. Chem. 2012, 4, 59-63. (38) Chang, Y.; Chang, W. J.; Shih, Y. J.; Wei, T. C.; Hsiue, G. H. Zwitterionic SulfobetaineGrafted Poly(vinylidene fluoride) Membrane with Highly Effective Blood Compatibility via


30

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Atmospheric Plasma-Induced Surface Copolymerization. ACS Appl. Mater. Interfaces 2011, 3, 1228-1237. (39) Beers, K. L.; Boo, S.; Gaynor, S. G.; Matyjaszewski, K. Atom Transfer Radical Polymerization of 2-Hydroxyethyl Methacrylate. Macromolecules 1999, 32, 5772-5776. (40) Zhao, Q.; Ni, P. Synthesis of Well-Defined and Near Narrow-Distribution Diblock Copolymers Comprising PMMA and PDMAEMA via Oxyanion-Initiated Polymerization. Polymer 2005, 46, 3141-3148. (41) Hester, J.; Banerjee, P.; Won, Y.-Y.; Akthakul, A.; Acar, M.; Mayes, A. ATRP of Amphiphilic Graft Copolymers Based on PVDF and Their Use as Membrane Additives. Macromolecules 2002, 35, 7652-7661. (42) Hester, J.; Mayes, A. Design and Performance of Foul-Resistant Poly (vinylidene fluoride) Membranes Prepared in a Single-Step by Surface Segregation. J. Membr. Sci. 2002, 202, 119-135. (43) Hashim, N. A.; Liu, F.; Li, K. A Simplified Method for Preparation of Hydrophilic PVDF Membranes from an Amphiphilic Graft Copolymer. J. Membr. Sci. 2009, 345, 134-141. (44) Hester, J.; Banerjee, P.; Mayes, A. Preparation of Protein-Resistant Surfaces on Poly (vinylidene fluoride) Membranes via Surface Segregation. Macromolecules 1999, 32, 16431650. (45) Hashim, N. A.; Liu, Y.; Li, K. Preparation of PVDF Hollow Fiber Membranes using SiO2 Particles: The Effect of Acid and Alkali Treatment on the Membrane Performances. Ind. Eng. Chem. Res. 2011, 50, 3035-3040.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 34

(46) Zhang, F.; Zhang, W.; Yu, Y.; Deng, B.; Li, J.; Jin, J. Sol–Gel Preparation of PAA-gPVDF/TiO 2 Nanocomposite Hollow Fiber Membranes with Extremely High Water Flux and Improved Antifouling Property. J. Membr. Sci. 2013, 432, 25-32. (47) Tao, M.; Liu, F.; Xue, L. Hydrophilic Poly(vinylidene fluoride) (PVDF) Membrane by in Situ Polymerisation of 2-Hydroxyethyl Methacrylate (HEMA) and Micro-Phase Separation. J. Mater. Chem. 2012, 22, 9131. (48) Deng, B.; Yu, M.; Yang, X.; Zhang, B.; Li, L.; Xie, L.; Li, J.; Lu, X. Antifouling Microfiltration Membranes Prepared from Acrylic Acid or Methacrylic Acid Grafted Poly(vinylidene fluoride) Powder Synthesized via Pre-irradiation

Induced Graft

Polymerization. J. Membr. Sci. 2010, 350, 252-258. (49) Chiang, Y.-C.; Chang, Y.; Higuchi, A.; Chen, W.-Y.; Ruaan, R.-C. Sulfobetaine-Grafted Poly(vinylidene fluoride) Ultrafiltration Membranes Exhibit Excellent Antifouling Property. J. Membr. Sci. 2009, 339, 151-159. (50) Sun, Q.; Su, Y.; Ma, X.; Wang, Y.; Jiang, Z. Improved Antifouling Property of Zwitterionic Ultrafiltration Membrane Composed of Acrylonitrile and Sulfobetaine Copolymer. J. Membr. Sci. 2006, 285, 299-305. (51) Demirelli, K.; Coşkun, M. Synthesis, Characterization and Thermal Degradation of Poly [2‐(3‐p‐bromophenyl‐3‐methylcyclobutyl)‐2‐hydroxyethylmethacrylate]. Polym. Int. 1999, 48, 1244-1250. (52) Wei, Q.; Wang, X.; Zhou, F. A Versatile Macro-Initiator with Dual Functional Anchoring Groups for Surface-Initiated Atom Transfer Radical Polymerization on Various Substrates. Polym.Chem. 2012, 3, 2129-2137.


32

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(53) Liu, B.; Sun, S.; Gao, Z.; Zhang, D.; Bian, G.; Qi, Y.; Yang, X.; Li, C. Silica-g-poly[2(N,N-dimethyl amino) ethyl methacrylate] Hybrid Nanospheres with Polymer Brushes as Stabilizer for Metallic Nanocolloids. Colloids Surf., A 2014, 456, 195-202. (54) Lee, S. W.; Kim, B.-S.; Chen,S.; Shao-Horn,Y.; Hammond, P. T. Layer-by-Layer Assembly of All Carbon Nanotube Ultrathin Films for Electrochemical Applications. J. Am. Chem. Soc. 2009, 131, 671-679 (55) Wang, Z. X.; Jin, J.; Hou, D. Y.; Lin, S. H. Tailoring Surface Charge and Wetting Property for Robust Oil-Fouling Mitigation in Membrane Distillation. J. Membr. Sci. 2016, 516, 113122.


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Table of Contents Graphic


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Superhydrophilic In-Situ-Cross-Linked Zwitterionic Polyelectrolyte

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