Functional and surface-active membranes from poly(vinylidene fluoride)-graft-poly(acrylic acid) prepared via RAFT-mediated graft copolymerization

Chain-Extendable Crosslinked Hydrogels Using Branching RAFT Modification

Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition–fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA–EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Polymeric Membranes for Biomedical Applications

Polymeric membranes are selective materials used in a wide range of applications that require separation processes, from water filtration and purification to industrial separations. Because of these materials' remarkable properties, namely, selectivity, membranes are also used in a wide range of biomedical applications that require separations. Considering the fact that most organs (apart from the heart and brain) have separation processes associated with the physiological function (kidneys, lungs, intestines, stomach, etc.), technological solutions have been developed to replace the function of these organs with the help of polymer membranes. This review presents the main biomedical applications of polymer membranes, such as hemodialysis (for chronic kidney disease), membrane-based artificial oxygenators (for artificial lung), artificial liver, artificial pancreas, and membranes for osseointegration and drug delivery systems based on membranes.

Facile Fabrication of Superwetting PVDF Membrane for Highly Efficient Oil/Water Separation

A novel superhydrophilic and underwater superoleophobic modified PVDF membrane for oil/water separation was fabricated through a modified blending approach. Pluronic F127 and amphiphilic copolymer P (MMA-AA) were directly blended with PVDF as a hydrophilic polymeric additive to prepare membranes via phase inversion induced by immersion precipitation. Then, the as-prepared microfiltration membranes were annealed at 160 °C for a short time and quenched to room temperature. The resultant membranes exhibited contact angles of hexane larger than 150° no matter whether in an acidic or basic environment. For 1, 2-dichloroethane droplets, the membrane surface showed a change from superoleophilic to superoleophobic under water with aqueous solutions with pH values from 2 to 13. This as-prepared membrane has good mechanical strength and can then be applied for oil and water mixture separation.

Highly Effective Anti-Organic Fouling Performance of a Modified PVDF Membrane Using a Triple-Component Copolymer of P(Stx-co-MAAy)-g-fPEGz as the Additive

In this study, a triple-component copolymer of P(St_x-co-MAA_y)-g-fPEG_z containing hydrophobic (styrene, St), hydrophilic (methacrylic acid, MAA), and oleophobic (perfluoroalkyl polyethylene glycol, fPEG) segments was synthesized and used as an additive polymer to prepare modified PVDF membrane for enhanced anti-fouling performance. Two compositions of St:MAA at 4:1 and 1:1 for the additive and two blending ratios of the additive:PVDF at 1:9 and 3:7 for the modified membranes were specifically examined. The results showed that the presence of the copolymer additive greatly affected the morphology and performance of the modified PVDF membranes. Especially, in a lower ratio of St to MAA (e.g., St:MAA at 1:1 versus 4:1), the additive polymer and therefore the modified PVDF membrane exhibited both better hydrophilic as well as oleophobic surface property. The prepared membrane can achieve a water contact angle at as low as 48.80° and display an underwater oil contact angle at as high as 160°. Adsorption experiments showed that BSA adsorption (in the concentration range of 0.8 to 2 g/L) on the modified PVDF membrane can be reduced by as much as 93%. From the filtration of BSA solution, HA solution, and oil/water emulsion, it was confirmed that the obtained membrane showed excellent resistance to these organic foulants that are often considered challenging in membrane water treatment. The performance displayed slow flux decay during filtration and high flux recovery after simple water cleaning. The developed membrane can therefore have a good potential to be used in such applications as water and wastewater treatment where protein and other organic pollutants (including oils) may cause severe fouling problems to conventional polymeric membranes.

Visible light-induced controlled surface grafting polymerization of hydroxyethyl methacrylate from isopropylthioxanthone semipinacol-terminated organic monolayers

Reaction scheme of the visible light-induced controlled surface grafting polymerization of methacrylate monomers onto organosilane-coated silicon initiated by previously coupled dormant ITXSP groups.

Thermo-responsive adsorption-desorption of perfluoroorganics from water using PNIPAm hydrogels and pore functionalized membranes

Perfluorochemicals (PFCs) are emerging contaminants in various water sources. Responsive polymers provide a new avenue for PFC adsorption/desorption from water. Poly-N-isopropylacrylamide's (PNIPAm's) temperature-responsive behavior and hydrophilic/hydrophobic transition is leveraged for reversible adsorption and desorption of PFCs. Adsorption of PFOA (perfluoro-octanoic acid) onto PNIPAm hydrogels yielded Freundlich distribution coefficients (K_d) of 0.073 L/g at 35 °C (above LCST) and 0.026 L/g at 22°C. Kinetic studies yielded second order rate constants (k₂) of 0.012 g/mg/h for adsorption and 12.6 g/mg/h for desorption, with initial rates of 28 mg/g/h and 41 mg/g/h, respectively. Interaction parameters of PNIPAm's functional groups in its different conformational states, as well as the hydrophobic fluorinated carbon tails and hydrophilic head groups of PFOA are used to describe relative adsorption. Polyvinylidene difluoride (PVDF) provides a robust membrane structure for the commercial viability of polymeric adsorbents. Temperature swing adsorption of PFOA using PNIPAm functionalized PVDF membrane pores showed consistent adsorption and desorption capacity over 5 cycles. PFOA desorption percentage of 60% was obtained in pure water at temperatures below PNIPAm's lower critical solution temperature (LCST) while 13% desorption was obtained at temperatures above the LCST, thus showing the importance of the LCST on desorption performance.

Role of membrane pore polymerization conditions for pH responsive behavior, catalytic metal nanoparticle synthesis, and PCB degradation

This article describes the effects of changing monomer and cross-linker concentrations on the mass gain, water permeability, Pd-Fe nanoparticle (NP) loading, and the rate of degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) of pore functionalized polyvinylidene fluoride (PVDF) membranes. In this study, monomer (acrylic acid (AA)) and cross-linker (N, N'- methylene-bis (acrylamide)) concentrations were varied from 10 to 20 wt% of polymer solution and 0.5-2 mol% of monomer concentration, respectively. Results showed that responsive behavior of membrane could be tuned in terms of water permeability over a range of 270-1 L m-2 h-1 bar-1, which is a function of water pH. The NP size on the membrane surface was found in the range of 16-23 nm. With increasing cross-linker density the percentage of smaller NPs (< 10 nm) increases due to smaller mesh size formation during in-situ polymerization of membrane. NP loading was found to vary from 0.21 to 0.94 mg per cm2 of membrane area depending on the variation of available carboxyl groups in membrane pore domain. The NPs functionalized membranes were then tested for use as a platform for the degradation of PCB 126. The observed batch reaction rate (Kobs) for PCB 126 degradation for per mg of catalyst loading was found 0.08-0.1 h-1. Degradation study in convective flow mode shows 98.6% PCB 126 is degraded at a residence time of 46.2 s. The corresponding surface area normalized reaction rate (K sa ) is found about two times higher than K sa of batch degradation; suggesting elimination of the effect of diffusion resistance for degradation of PCB 126 in convective flow mode operation. These Pd-Fe-PAA-PVDF membranes and nanoparticles are characterized by TGA, contact angle measurement, surface zeta potential, XRD, SEM, XPS, FIB, TEM and other techniques reveal the details about the membrane surface, pores and nanoparticles size, shape and size-distribution. Statistical analysis based on experimental results allows us to depict responsive behavior of functionalized membrane. In our best knowledge this paper first time reports detail study on responsive behavior of pore functionalized membrane in terms of permeability, NPs size, metal loading and its effect on PCB 126 degradation in a quantified approach.

Construction of Hierarchical Fouling Resistance Surfaces onto Poly(vinylidene fluoride) Membranes for Combating Membrane Biofouling

Owing to the highly hydrophobic nature, fluoropolymer membranes usually suffer from serious fouling problem, and therefore largely limited their practical applications. Also, the development of environmentally benign and nonreleasing antifouling coatings onto the inert fluoropolymer membranes remains a great challenge and is of prime importance for various scientific interests and industrial applications. In the present work, a facile and effective approach for the construction of hierarchical fouling resistance surfaces onto the poly(vinylidene fluoride) (PVDF) membranes was developed. Graft copolymers of PVDF with poly(hyperbranched polyglycerol methacrylamide) side chains (PVDF-g-PHPGMA copolymers) were synthesized via reversible addition-fragmentation chain transfer (RAFT) graft copolymerization of pentafluorophenyl methacrylate (PFMA) with the ozone-preactivated PVDF, followed by activated ester-amine reaction of PPFMA chains with amino-terminated hyperbranched polyglycerol (HPG-NH₂). The copolymers could be simply processed into microfiltration (MF) membranes with surface-tethered PHPGMA side chains on the membrane and pore surfaces by nonsolvent induced phase inversion. Furthermore, the PVDF-g-PHPGMA-g-PSBMA membrane was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) of zwitterionic monomer, N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine (SBMA) from the PVDF-g-PHPGMA membrane and pore surfaces. Arise from a synergistic effect of the dendritic architecture of PHPGMA branches and "superhydrophilic" nature of PSBMA brushes, the PVDF-g-PHPGMA-g-PSBMA membranes exhibit superior resistance to protein and bacteria adhesion with insignificant cytotoxicity effects, making the membranes potentially useful for water treatment and biomedical applications. One may find the present study a general and effective method for the fabrication of antifouling fluoropolymer membranes in a controllable and green manner.

From pH- to Light-Response: Postpolymerization Modification of Polymer Brushes Grafted onto Microporous Polymeric Membranes

A microporous pH- and light-responsive membrane that enables remote control over its interfacial properties has been fabricated. pH-Responsiveness was imparted to a porous polypropylene film via grafting of poly(methacrylic acid) brushes from the substrate using argon-plasma-induced free-radical graft polymerization. Morphological changes as a function of grafting level were analyzed using atomic force microscopy. Conversion into a light-responsive membrane was performed via postpolymerization modification to covalently attach photochromic spiropyran moieties to the grafted polymer brushes. Reversible switches in wettability and permeability were determined upon changing from acidic to basic pH or upon alternating UV- and visible-light irradiation. Additionally, light-responsive membranes show a switch in color upon UV exposure.

Direct surface modification of poly(VDF-co-TrFE) films by surface-initiated ATRP without pretreatment

A NMR study revealed that the surface-initiated ATRP of tBA occurred due to fluorine abstraction from the TrFE units of poly(VDF-co-TrFE).

Water soluble poly(styrene sulfonate)-b-poly(vinylidene fluoride)-b-poly(styrene sulfonate) triblock copolymer nanoparticles

Water-soluble PNaSS-b-PVDF-b-PNaSS triblock copolymer.

Preparation and characterization of Pd/Fe bimetallic nanoparticles immobilized on Al2O3/PVDF membrane: Parameter optimization and dechlorination of dichloroacetic acid

Using a liquid-solid phase inversion method, a hybrid matrix poly(vinylidene fluoride) (PVDF) membrane was prepared with alumina (Al2O3) nanoparticle addition. Pd/Fe nanoparticles (NPs) were successfully immobilized on the Al2O3/PVDF membrane, which was characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The micrographs showed that the Pd/Fe NPs were dispersed homogeneously. Several important experimental parameters were optimized, including the mechanical properties, contact angle and surface area of Al2O3/PVDF composite membranes with different Al2O3 contents. At the same time, the ferrous ion concentration and the effect of hydrophilization were studied. The results showed that the modified Al2O3/PVDF membrane functioned well as a support. The Al2O3/PVDF membrane with immobilized Pd/Fe NPs exhibited high efficiency in terms of dichloroacetic acid (DCAA) dechlorination. Additionally, a reaction pathway for DCAA dechlorination by Pd/Fe NPs immobilized on the Al2O3/PVDF membrane system was proposed.

Synthesis of Chlorotrifluoroethylene-Based Block Copolymers by Iodine Transfer Polymerization

Various fluorinated macro-chain transfer agents (CTAs) based on vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), or CTFE and vinylidene chloride (VDC), were synthesized by iodine transfer polymerization (ITP). These macro-CTAs were involved in a further ITP reaction that led to the synthesis of original CTFE-based block copolymers exhibiting molecular weight ranging from 2500 to 40000 g/mol and endowed with high thermal stabilities (decomposition temperature at 10% weight loss of ca. 380 °C, under air). ITP of CTFE and VDC as well as ITP of VDF thermally initiated at 100 °C by a catalytic amount of dimanganese decacarbonyl (Mn₂(CO)₁₀) are reported for the first time.

Development of Bench and Full-Scale Temperature and pH Responsive Functionalized PVDF Membranes with Tunable Properties

Temperature and pH responsive polymers (poly(N-isopropylacrylamide) (PNIPAAm), and polyacrylic acid, PAA) were synthesized in one common macrofiltration PVDF membrane platform by pore-filling method. The microstructure and morphology of the PNIPAAm-PVDF, and PNIPAAm-FPAA-PVDF membranes were studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The membrane pore size was controlled by the swelling and shrinking of the PNIPAAm at the temperature around lower critical solution temperature (LCST). The composite membrane demonstrated a rapid and reversible swelling and deswelling change within a small temperature range. The controllable flux makes it possible to utilize this temperature responsive membrane as a valve to regulate filtration properties by temperature change. Dextran solution (Mw=2,000,000g/mol, 26 nm diameter) was used to evaluate the separation performance of the temperature responsive membranes. The ranges of dextran rejection are from 4% to 95% depending on the temperature, monomer amount and pressure. The full-scale membrane was also developed to confirm the feasibility of our bench-scale experimental results. The full-scale membrane also exhibited both temperature and pH responsivity. This system was also used for controlled nanoparticles synthesis and for dechlorination reaction.

Nanomaterials for membrane fouling control: accomplishments and challenges

We report a review of recent research efforts on incorporating nanomaterials-including metal/metal oxide nanoparticles, carbon-based nanomaterials, and polymeric nanomaterials-into/onto membranes to improve membrane antifouling properties in biomedical or potentially medical-related applications. In general, nanomaterials can be incorporated into/onto a membrane by blending them into membrane fabricating materials or by attaching them to membrane surfaces via physical or chemical approaches. Overall, the fascinating, multifaceted properties (eg, high hydrophilicity, superparamagnetic properties, antibacterial properties, amenable functionality, strong hydration capability) of nanomaterials provide numerous novel strategies and unprecedented opportunities to fully mitigate membrane fouling. However, there are still challenges in achieving a broader adoption of nanomaterials in the membrane processes used for biomedical applications. Most of these challenges arise from the concerns over their long-term antifouling performance, hemocompatibility, and toxicity toward humans. Therefore, rigorous investigation is still needed before the adoption of some of these nanomaterials in biomedical applications, especially for those nanomaterials proposed to be used in the human body or in contact with living tissue/body fluids for a long period of time. Nevertheless, it is reasonable to predict that the service lifetime of membrane-based biomedical devices and implants will be prolonged significantly with the adoption of appropriate fouling control strategies.

Simple fluidic system for purifying and concentrating diagnostic biomarkers using stimuli-responsive antibody conjugates and membranes

We report a simple fluidic system that can purify and concentrate diagnostic biomarkers through the capture and triggered release of stimuli-responsive polymer-antibody conjugates at porous membranes that are grafted with the same stimuli-responsive polymer. This technique is applied here to the capture and detection of a model streptavidin antigen and subsequently to clinical ranges of the malaria antigen Plasmodium falciparum histidine-rich protein 2 (PfHRP2) from spiked human plasma. The carboxyl end-groups of semi-telechelic poly(N-isopropylacrylamide) (pNIPAAm) synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization were modified with tetrafluorophenol to yield amine-reactive ester groups for conjugation to amine groups of anti-streptavidin and anti-PfHRP2 antibodies. Stimuli-responsive membranes were constructed from 1.2 μm pore-size, hydroxylated, nylon-6,6 filters (Loprodyne, from Pall Corporation). The surface hydroxyl groups on the filters were conjugated to a 2-ethylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (EMP) RAFT chain transfer agent, and the surface-grafted pNIPAAm was obtained by subsequent polymerization. The number average molecular weight (Mn) and polydispersity indices (PDI) of the surface grafts were characterized, and membranes with either 4100 and 8400 dalton pNIPAAm grafts showed greater than 80% anti-streptavidin capture efficiency. The 8400 dalton-graft membrane showed the highest release efficiency, and it was demonstrated that at 0.2 nM starting concentration the streptavidin could be concentrated approximately 40-fold by releasing into a small 50 μL volume. This concentrator system was applied to the capture and concentration of the PfHRP2 antigen, and results showed that the PfHRP2 antigen could be processed and detected at clinically relevant concentrations of this malaria biomarker.