Bao-Ku Zhu

Surface Characteristics of a Self-Polymerized Dopamine Coating Deposited on Hydrophobic Polymer Films

This study aims to explore the fundamental surface characteristics of polydopamine (pDA)-coated hydrophobic polymer films. A poly(vinylidene fluoride) (PVDF) film was surface modified by dip coating in an aqueous solution of dopamine on the basis of its self-polymerization and strong adhesion feature. The self-polymerization and deposition rates of dopamine on film surfaces increased with increasing temperature as evaluated by both spectroscopic ellipsometry and scanning electronic microscopy (SEM). Changes in the surface morphologies of pDA-coated films as well as the size and shape of pDA particles in the solution were also investigated by SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface roughness and surface free energy of pDA-modified films were mainly affected by the reaction temperature and showed only a slight dependence on the reaction time and concentration of the dopamine solution. Additionally, three other typical hydrophobic polymer films of polytetrafluoroethylene (PTFE), poly(ethylene terephthalate) (PET), and polyimide (PI) were also modified by the same procedure. The lyophilicity (liquid affinity) and surface free energy of these polymer films were enhanced significantly after being coated with pDA, as were those of PVDF films. It is indicated that the deposition behavior of pDA is not strongly dependent on the nature of the substrates. This information provides us with not only a better understanding of biologically inspired surface chemistry for pDA coatings but also effective strategies for exploiting the properties of dopamine to create novel functional polymer materials.

Antifouling and Antimicrobial Polymer Membranes Based on Bioinspired Polydopamine and Strong Hydrogen-Bonded Poly(N-vinyl pyrrolidone)

A facile and versatile approach for the preparation of antifouling and antimicrobial polymer membranes has been developed on the basis of bioinspired polydopamine (PDA) in this work. It is well-known that a tightly adherent PDA layer can be generated over a wide range of material surfaces through a simple dip-coating process in dopamine aqueous solution. The resulting PDA coating is prone to be further surface-tailored and functionalized via secondary treatments because of its robust reactivity. Herein, a typical hydrophobic polypropylene (PP) porous membrane was first coated with a PDA layer and then further modified by poly(N-vinyl pyrrolidone) (PVP) via multiple hydrogen-bonding interactions between PVP and PDA. Data of water contact angle measurements showed that hydrophilicity and wettability of the membranes were significantly improved after introducing PDA and PVP layers. Both permeation fluxes and antifouling properties of the modified membranes were enhanced as evaluated in oil/water emulsion filtration, protein filtration, and adsorption tests. Furthermore, the modified membranes showed remarkable antimicrobial activity after iodine complexation with the PVP layer. The PVP layer immobilized on the membrane had satisfying long-term stability and durability because of the strong noncovalent forces between PVP and PDA coating. The strategy of material surface modification reported here is substrate-independent, and applicable to a broad range of materials and geometries, which allows effective development of materials with novel functional coatings based on the mussel-inspired surface chemistry.

Surface modification of PVDF porous membranes via poly(DOPA) coating and heparin immobilization.

Based on the strong adhesive behavior of poly(3,4-dihydroxy-l-phenylalanine) (or poly(DOPA)) on solid surface, poly(vinylidene fluoride) (PVDF) microporous membranes were surface-modified by the self-polymerization of DOPA in aqueous solution. Subsequently, heparin was immobilized covalently onto the obtained PVDF/poly(DOPA) composite membranes by the coupling between heparin and poly(DOPA) coating. The modified membranes were subjected to a long-term washing, and the firm immobilization of poly(DOPA) and heparin was confirmed by X-ray photoelectron spectroscopy (XPS). The results of water contact angle measurements showed that the hydrophilicity of PVDF membranes was significantly improved by the incorporation of poly(DOPA) and heparin. The effects of poly(DOPA) and heparin on membrane surface morphologies were also investigated by scanning electron microscopy (SEM).

Immobilization of bovine serum albumin onto porous polyethylene membranes using strongly attached polydopamine as a spacer

Based on the self-polymerization and strong adhesion characteristics of dopamine in aqueous solution, a novel and convenient approach was developed to immobilize protein onto porous polyethylene (PE) membranes. A thin polydopamine (pDA) layer was formed and tightly coated onto PE membrane by dipping simply the membrane into dopamine aqueous solution for a period of time. Subsequently, bovine serum albumin (BSA) was bound onto the obtained PE/pDA composite membranes via the coupling between BSA and the reactive polydopamine layer. The firm immobilization of polydopamine layer and BSA was verified by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The results of water contact angle measurement showed that the hydrophilicity of PE membrane was significantly improved after coating polydopamine and binding BSA. The experiments of blood platelet adhesion indicated that BSA-immobilized PE membrane had better blood compatibility than the unmodified PE and the PE/pDA composite membranes. The investigations on hepatocyte cultures and cell viability revealed that the polydopamine coating endowed PE membrane with significantly improved cell compatibility. Compared to BSA surface, polydopamine surface is more favorable for cell adhesion, growth, and proliferation.

Anti-fouling and anti-bacterial polyethersulfone membranes quaternized from the additive of poly(2-dimethylamino ethyl methacrylate) grafted SiO2 nanoparticles

Anti-fouling and anti-bacterial polyethersulfone (PES) membranes were developed by the addition of poly(2-dimethylaminoethyl methacrylate) grafted silica nanoparticles (SiO2-g-PDMAEMA NPs) and further post-quaternization. The SiO2-g-PDMAEMA NPs were first synthesized by grafting PDMAEMA brushes from SiO2 NPs via surface-initiated, reversible addition fragmentation chain transfer (RAFT) polymerization. PES/SiO2-g-PDMAEMA hybrid ultrafiltration (UF) membranes were then prepared from the blending solutions of PES and SiO2-g-PDMAEMA NPs via non-solvent induced phase separation (NIPS) process. The PDMAEMA chains incorporated into the PES membranes were further quaternized by reacting with 1,3-propane sultone (1,3-PS) and methyl iodide (CH3I), respectively. After treatment with 1,3-PS, the resulting zwitterionic PES membranes exhibited excellent hydrophilicity, water permeability, solute rejection and protein anti-fouling properties. The cationic membranes obtained from CH3I treatment showed strong anti-bacterial activity against Escherichia coli (E. coli) and Staphyloccocus aureus Rosenbach (S. aureus). This work presents a convenient strategy for anti-biofouling modification of polymer membranes via surface quaternization of the reactive SiO2-g-PDMAEMA NPs additive.

HYDROPHILIC NANOFILTRATION MEMBRANES WITH SELF-POLYMERIZED AND STRONGLY-ADHERED POLYDOPAMINE AS SEPARATING LAYER *

Inspired by the self-polymerization and strong adhesion characteristics of dopamine in aqueous conditions, a novel hydrophilic nanofiltration (NF) membrane was fabricated by simply dipping polysulfone (PSf) ultrafiltration (UF) substrate in dopamine solution. The changes in surface chemical composition and morphology of membranes were determined by Fourier transform infrared spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experimental results indicated that the self-polymerized dopamine formed an ultrathin and defect-free barrier layer on the PSf UF membrane. The surface hydrophilicity of membranes was evaluated through water contact angle measurements. It was found that membrane hydrophilicity was significantly improved after coating a polydopamine (pDA) layer, especially after double coating. The dyes filtration experiments showed that the double-coated membranes were able to reject completely the dyes of brilliant blue, congo red and methyl orange with a pure water flux of 83.7 L/(m2·h) under 0.6 MPa. The zeta potential determination revealed the positively-charged characteristics of PSf/pDA composite membrane in NF process. The salt rejection of the membranes was characterized by 0.01 mmol/L of salts filtration experiment. It was demonstrated that the salts rejections followed the sequence: NaCl < Na2SO4 < MgSO4 < MgCl2 < CaCl2, and the rejection to CaCl2 reached 68.7%. Moreover, the composite NF membranes showed a good stability in water-phase filtration process.

Antifouling properties of poly(vinyl chloride) membranes modified by amphiphilic copolymers P(MMA-b-MAA)

Three well-defined diblock copolymers of poly(methyl methacrylate-b-methacrylic acid) (P(MMA-b-MAA)) were synthesized using atom transfer radical polymerization method and varying poly(methacrylic acid) (PMAA) chain lengths. These copolymers were blended with PVC to fabricate porous membranes via phase inversion process. Membrane morphologies were observed by scanning electron microscopy (SEM), and chemical composition changes of the membrane surfaces were measured by X-ray photoelectron spectroscopy (XPS). Static and dynamic protein adsorption experiments were used to evaluate antifouling properties of the blend membranes. It was found that, the blend membranes containing longer PMAA arm length showed lower static protein adsorption, higher water permeation flux and better protein solution flux recovery.

Progress in polymeric separators for lithium ion batteries

This study reviews the recent developments and the characteristics of polymeric separators used for lithium ion batteries. According to the structure and composition of the separators, they are broadly divided into four types: (1) polyolefin microporous separators, (2) heterochain polymer microporous separators, (3) polymer electrolytes and (4) non-woven separators. In particular, polymer electrolytes were defined as one category of separators for convenient description in this review; these feature intermediates between the two electrodes and possess transport properties comparable with the separator in liquid LIBs. For each category, the structure, characteristics, modification, and performance of separators are described. Finally, guidelines for further improvements in this research are outlined.

Improving the wettability and thermal resistance of polypropylene separators with a thin inorganic-organic hybrid layer stabilized by polydopamine for lithium ion batteries

This study aims to improve the wettability and thermal resistance of polypropylene (PP) separators for lithium ion batteries. The PP separator was first coated with polydopamine (PDA) on the basis of mussel-inspired surface chemistry. Then a thin inorganic–organic hybrid layer was immobilized onto the PDA-coated separator via a sol–gel process using tetraethoxysilane (TEOS) solutions. This method does not need any commonly-used polymeric binders because of the unique adhesion behaviour of the PDA intermediate layer, which greatly reduces the thickness of the modification layer and avoids excessive pore blocking. Owing to the incorporation of the hybrid layer, the composite separators showed better affinity with the liquid electrolyte and obvious reduction in thermal shrinkage in comparison to the unmodified separator. And the battery performances, such as interfacial resistance, discharge capacity and C-capacity were all improved after modification. Considering the effective adhesion of PDA onto nearly all kinds of separator/membrane surfaces, this modification strategy can be widely used without causing any obvious damage to the mechanical strength of the unmodified separators/membranes.

Gel polymer electrolyte-based on PVDF/fluorinated amphiphilic copolymer blends for high performance lithium-ion batteries

This paper describes the preparation and properties of PVDF/P(hexafluorobutyl methacrylate-co-poly(ethyleneglycol)methacrylate)(P(HFBMA-co-PEGMA)) blend gel polymer electrolyte (GPE) for high-performance lithium-ion batteries. The fluorinated amphiphilic copolymer, P(HFBMA-co-PEGMA), was synthesized by simple radical polymerization and then blended into poly(vinylidene fluoride) (PVDF) matrix via immersion phase inversion process. The composition, morphologies, liquid electrolyte uptake of the blend membranes and electrochemical properties of the corresponding GPEs were systematically investigated. It is found that the introduction of P(HFBMA-co-PEGMA) results in a slight increase in porosity, a reduction in crystallinity and better affinity with liquid electrolyte, which consequently lead to a substantial increase in liquid electrolyte uptake and ion conductivity. For the membrane with P(HFBMA-co-PEGMA)/PVDF mass ratio in 1.7/10, the liquid electrolyte uptake and ionic conductivity reach to 387% and 3.19 mS cm−1, respectively. In addition, the resulting GPE is electrochemically stable up to about 4.5 V (vs. Li+/Li).