Solution-cast Nafion ionomer membranes: preparation and characterization

Perfluorosulfonate ionomer dispersions in three different solvents (ethylene glycol (EG), dimethyl sulfoxide (DMSO) and dimethylformamide (DMF)) were used to prepare solution-cast membranes. The dispersions were obtained by dissolution of Nafion^® 112 membranes in a reactor using a water-ethanol solution. Measurements of water uptake and solubility of the cast membranes were conducted. Conductivities were measured directly on carbon paper/membrane/carbon paper assemblies fully immersed in deionized water and were registered by means of impedance spectroscopy as a function of temperature. Results show that all cast samples have lower chemical stability than commercial membranes. Moreover, only membranes cast from dimethylformamide-based dispersions gave conductivity performance comparable to those of Nafion^® 112 and 115. Casting process from dispersion obtained using Nafion^® rejects gave better results than the process utilizing commercial dispersion.     

Preparation of silver/hydroxyapatite nanocomposite spheres

The silver nanoparticles of 7 nm in diameter were controlled to be synthesized under the cooperation of the ethylenediamine and the cetyl trimethyl ammonium bromide (CTAB). Then, under the electrostatic effect of the silver nanoparticles and with the strong adsorbability of the hydroxyapatite nanoribbon spherites, the two substances were combined to form special nanocomposite spheres.     

Preparation and characterization of proton conducting polysulfone grafted poly(styrene sulfonic acid) polyelectrolyte membranes

The syntheses of series of proton conducting comb copolymer membrane involving polysulfone back bone as main chain and poly(styrene sulfonic acid) (PSSA) being side chain, i.e. polysulfone grafted poly(styrene sulfonic acid) (PSU-g-PSSA) are presented. Chloromethylation of the polysulfone backbone was done by Fridel Craft alkylation reaction. Atom transfer radical polymerization was used for control grafting from the chloromethylated positions. The successful substitution of the chloromethyl group and its grafting with PSSA was characterized by elemental analysis and proton nuclear magnetic resonance. Water uptake, electrochemical properties like ion exchange capacity (IEC) and proton conductivities increase with increase in PSSA contents. Thermal gravimetric analysis (TGA) showed the thermal stability of membranes up to 250 °C. Proton conductivity for maximum amount of grafting is 0.02 S/cm.     

Impact of acid containing montmorillonite on the properties of Nafion membranes

The counter-ions of montmorillonite have been exchanged for ammonium cations containing either a sulfonic acid or a carboxylic acid in order to improve the performances of sulfonated membranes in direct methanol fuel cell. These layered silicates have been dispersed within Nafion^® by solution mixing. Comparison with conventional organo-modified montmorillonite (Cloisite 30B) shows that the incorporation of carboxylic acid in the clay galleries improves the filler dispersion and, consequently, the methanol barrier properties. Moreover, the negative impact of Cloisite 30B on the ionic conductivity is restricted.     

Dehydration of isopropanol by PVA-APTEOS/TEOS nanocomposite membranes

In the present work, dehydration of isopropanol was investigated by novel organic-inorganic nanocomposite membranes which were prepared through sol-gel reaction of polyvinyl alcohol (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) and tetraethoxysilane (TEOS). The PVA chains were crosslinked by mixing silane coupling agents. This reaction between polymer chains and silanols agents could control degree of swelling of the nanocomposite membranes in aqueous isopropanol (IPA) solutions. The membranes were characterized by SEM and ATIR. Effects of APTEOS content in the membranes, feed concentration and temperature on pervaporation (PV) performance were investigated. It was found out that separation factor and permeation flux increase with increasing APTEOS content in the membranes. Arrhenius-type relationship was used for describing the temperature dependence of permeation flux. It was also found out that separation factor decreases with increasing temperature.     

Preparation and characterization of magnetite/hydroxyapatite/chitosan nanocomposite by in situ compositing method

Chitosan is an important kind of biomaterial that is widely used in medical applications. One of the key concerns about its use is the preparation of composites used for bone engineering. Aim of this study concerns the preparation of three‐dimensional nanocomposites having potential use in bone repair and regeneration. The magnetite/hydroxyapatite/chitosan nanocomposites were prepared via in situ compositing method by preparing precursor solutions and molds with chitosan membrane. These nanocomposites were characterized by chemical, spectroscopic, magnetic, and morphological methods. X‐ray diffraction analysis results demonstrate the formation of magnetite and hydroxyapatite in the chitosan matrix. FTIR analysis indicates that inorganic nanoparticles were chemically bound to the amino and hydroxyl groups in CS molecules. From TG/DTA data, it can be concluded that during preparation raw materials were almost perfectly incorporated into the nanocomposites, and the decrease in decomposition temperatures indicates the formation of chemical bonds between inorganic nanoparticles and chitosan molecules. TEM results show that the maximum size of inorganic particles in the magnetite/hydroxyapatite/chitosan nanocomposites was under 50 nm, and these particles were dispersed homogeneously in the chitosan matrix. From the magnetic measurement, it could be concluded that the nanocomposites were superparamagnetic, which is also the peculiarity of nanomagnetites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nafion/Analcime and Nafion/Faujasite composite membranes for polymer electrolyte membrane fuel cells

The Nafion/zeolite composite membranes were synthesized for polymer electrolyte fuel cells (PEMFCs) by adding zeolite in the matrix of Nafion polymer. Two kinds of zeolites, Analcime and Faujasite, having different Si/Al ratio were used. The physico-chemical properties of the composite membranes such as water uptake, ion-exchange capacity, hydrogen permeability, and proton conductivity were determined. The fabricated composite membranes showed the significant improvement of all tested properties compared to that of pure Nafion membrane. The maximum proton conductivity of 0.4373 S cm⁻¹ was obtained from Nafion/Analcime (15%) at 80 °C which was 6.8 times of pure Nafion (0.0642 S cm⁻¹ at 80 °C). Conclusively, Analcime exhibited higher improvement than Faujasite.     

Electrophoretic deposition of fiber hydroxyapatite/titania nanocomposite coatings

Hydroxyapatite/titania nanocomposite coatings were electrophoretically deposited from ethanolic suspensions of titania and fiber shaped hydroxyapatite (FHA) nanoparticles. Triethanolamine (TEA) was used to enhance the colloidal stability of particles in suspensions. Electrophoretic deposition (EPD) was performed using the suspensions with different concentrations (wt%) of titania/FHA particles. EPD rate decreased more rapidly with time for suspensions with higher wt% of FHA due to the higher voltage drop over the deposits shaped from them. Stacking of long FHA particles on the substrate during EPD resulted in the formation of coarse pores in the deposits. It was found that titania nanoparticles can more efficiently infiltrate through and fill the pores in TEA containing suspensions due to the stronger electrostatic repulsion force between pore walls (FHA) and titania nanoparticles in them. The coatings deposited from the suspensions with 50 wt% of FHA or more did not crack during drying due to the significant reinforcement action provided by high wt% of FHA in them. Nanocomposite coatings deposited from TEA containing (2 mL/L) suspensions with 50 and 75 wt% of FHA had the best corrosion resistance in simulated body fluid (SBF) solution due to their crack-free microstructure and efficiently filled pores.     

壳聚糖基聚电解质复合膜的制备及性能

为了克服壳聚糖薄膜力学强度差和在体液内降解太快的缺陷, 首先用"一步法"合成了—COOH含量及疏水性可控的苹果酸与乳酸共聚物(PML), 再将共聚物与壳聚糖(CS)复合, 通过溶液浇铸-挥发的方法制备改性复合薄膜。通过红外(FT-IR)、热重分析(TGA)、力学性能测试、降解实验及体外细胞毒性实验等方法对复合膜进行分析, 研究L-苹果酸(MA)与D,L-乳酸(LA)的投料比(n_MA:n_LA)对复合膜性能的影响。结果显示:当n_MA:n_LA为1:1.5时, 该共聚物与CS的复合膜拉伸强度达到54.8MPa, 断裂伸长率为10.7%, 质量损失50%所需时间为28天, 细胞相对增殖率为98.7%。研究表明:通过共聚物与壳聚糖之间的聚电解质相互作用, 有效形成了结构均匀、性能改善的薄膜, 复合膜的柔韧性提高, 降解时间适当延长, 性能可由共聚物的投料比来调节。复合膜无细胞毒性, 生物相容性好, 作为手术后防组织粘连材料具有光明的应用前景。     

In situ hybridization and characterization of fibrous hydroxyapatite/chitosan nanocomposite

Nano‐fibrous hydroxyapatite/chitosan (HA/CS) composites with HA contents of 0–70 wt % were prepared by in situ hybridization with a preprepared chitosan film as semipermeable membrane to slow down the hybridization process. The phase composition, microstructure, and morphology of the composites were characterized by means of Fourier transform infrared spectroscopy, X‐ray diffraction, and high‐resolution transmission electron microscopy. It was found that the in situ prepared inorganic phase was hydroxyapatite nano‐fibers that were uniformly dispersed in the chitosan matrix. The average diameter of the fibers were about 3 nm, while the length of the fibers increases from 20 to 60 nm when the hydroxyapatite content increased from 10 to 70 wt %. The compressive strength and Young's modulus of these nano‐fibrous HA/CS composites increased with the increasing HA content and reached the highest values of 170 and 1.7 GPa, respectively, at the HA content of 50–70 wt %, which were much higher than the values of samples prepared by coprecipitation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of UV-cured polyurethane acrylate/ZnO nanocomposite films based on surface modified ZnO

A series of polyurethane acrylate (PUA)/ZnO nanocomposite films with different ZnO contents were prepared via a UV-curing system. To ensure good dispersion in the PUA matrix, ZnO nanoparticles were modified with a silane coupling agent and confirmed by FT-IR analysis. The morphological structures, thermal properties, mechanical properties and water transfer properties of the prepared films were investigated as a function of their ZnO concentration. WAXD and SEM analyses showed that the surface-modified ZnO nanoparticles were homogeneously dispersed in the PUA matrix and the molecular ordering increased with increasing ZnO content. Compared with neat PUA, the hardness and elastic modulus in films increased from 0.03 to 0.056 GPa and from 2.75 to 3.55 GPa, respectively. Additionally, the water uptake and WVTR in the PUA/ZnO nanocomposite films decreased as the ZnO content nanoparticles increased, which may come from enhanced molecular ordering and hydrophobicity in films. UV light below approximately 450 nm can be efficiently absorbed by incorporating ZnO nanoparticles into a PUA matrix, indicating that these composite films exhibit good weather ability and UV-shielding effects. The enhanced physical properties achieved by incorporating modified ZnO nanoparticles can be advantageous in various applications, whereas the thermal stability of the composite films should be increased.     

Sorption and desorption of water vapour by membranes of the polyelectrolyte complex of chitosan and carboxymethyl cellulose

Sorption of water vapour by chitosan/carboxymethyl cellulose polyelectrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake (W) on time was observed for W values lower than 0.5 g of water per gram of membrane. For higher values of W diffusion becomes controlled by the relaxation of the chains, and second-order kinetics is observed. An equation that satisfactorily reproduces this behaviour is proposed. Desorption experiments were carried out at different temperatures and the W versus time curves obtained exhibited the same general pattern and were also adjusted by this equation. The approximate average diffusion coefficients were evaluated at each temperature and the apparent activation energy for the diffusion process is reported.     

Stoichiometric and nonstoichiometric polyelectrolyte complex of chitosan and polyethyleneglycol‐monosuccinate: Preparation and characterization

Stoichiometric and nonstoichiometric polyelectrolyte complex (PEC) was prepared with polyethylene glycol‐monosuccinate (PEGMS), and chitosan (CS). A series of PEGMS were synthesized by a 1 : 1 mol ratio between PEG and succinic anhydride. Then, the novel PEC was prepared by a various mole reaction of the above synthesized PEGMS and CS. The physicochemical properties of the synthesized PEC was characterized by using elemental analysis, FTIR, ¹H, and ¹³C nuclear magnetic resonance, dissolution behavior, and phase transition phenomenon. Furthermore, some properties of the PEC obtained were analyzed by UV‐Visible spectrometry, wide‐angle X‐ray diffraction, differential scanning calorimeter, scanning electron microscope, and estimated solubility, and cell viability assay, respectively. It was found that the observed FTIR, ¹H, and ¹³C‐NMR data was in good agreement with the chemical structure of the prepared PEGMS and PEC. The dissolution behaviors of nonstoichiometric PEC were found to depend on the pH of the solution as well as on the PEGMS/CS composition. The study of MTT assay suggested that the viability of HepG2 human hepatoblastoma cell on PEC were increased significantly in accordance with mole ratio of CS. As the results, the obtained several product is a useful intermediate, which permits further chemical modification for the amino group of CS and may have potential applications in biocompatible or cosmetic systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

新型温敏性中空纤维膜的制备与表征

采用自由基聚合方法对中空纤维膜（hollow fiber membranes,HFMs）进行了N-异丙基丙烯酰胺（NIPAAm）的接枝聚合,制备了一系列PNIPAAm-g-HFMs,同时考察了成纤维细胞在PNIPAAm-g-HFMs表面的培养与降温脱附情况。傅里叶红外光谱和元素分析结果表明PNIPAAm成功地在中空纤维膜上接枝聚合。动态接触角分析结果显示,当温度降至LCST以下,PNIPAAm-g-HFMs表面接触角明显降低;蛋白黏附测定结果进一步证实了当温度发生改变时,PNIPAAm-g-HFMs表面呈现亲疏水性质变化,即具有温敏性。37℃时,成纤维细胞在HFMs-0.005,HFMs-0.01和HFMs-0.05表面均能正常黏附、铺展与增殖;而HFMs-0.2不适宜细胞的黏附与生长。降温孵育后,黏附于PNIPAAm-g-HFMs表面的细胞发生明显的形态变化并从其表面发生脱附,细胞脱附率高达90%以上。以上实验结果表明,PNIPAAm-g-HFMs具有良好的温敏性,可实现细胞的降温脱附,可与生物反应器相结合用于贴壁型细胞的大规模扩增与降温收获。     

Rapid assembly of polyelectrolyte multilayer membranes using an automatic spray system

The layer‐by‐layer (LbL) assembly of polyelectrolyte multilayers on to a porous supporting membrane is able to create various new composite membranes. However, the low efficiency and long time required for such procedures limit practical applications. In this study, an automatic spray system has been constructed for the rapid assembly of polyelectrolyte multilayers on to nanoporous supporting membranes. The compounds polyacrylic acid and poly(ethyleneimine), used as a model polyelectrolyte pair, were alternately sprayed on to a polyacrylonitrile ultrafiltration membrane. Experiments proved that the composite membrane obtained in this way had a good pervaporation dehydration performance. In addition, the process times were dramatically decreased, by as much as 80 folds, when compared with classical dip‐LbL methods. Such an automated system can easily be converted to the assembly of various organic species. Therefore, it is a versatile and highly efficient system for manufacturing composite multilayer membranes for many separation applications. © 2012 American Institute of Chemical Engineers AIChE J, 59: 250–257, 2013     

Preparation and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coatings for biomedical applications

In order to improve biological and mechanical properties of hydroxyapatite, the concept of hydroxyapatite-included nanocomposite coatings was introduced. By judiciously choosing constituent ceramics for composites preparation, the biological and mechanical performance of coatings can be tailored in order to meet various clinical requirements. The aim of this work was fabrication, development and characterization of novel hydroxyapatite-forsterite-bioactive glass nanocomposite coatings. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to apply coating on 316L stainless steel (SS) by dip coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were used to investigate the phase structure, microstructure and morphology of the coating. In order to evaluate the forsterite incorporation influence upon bioactivity, the changes on the surfaces of the prepared composite coatings after the predicted days of contact with simulated body fluid (SBF) were investigated by SEM. Results showed that the suitable calcined temperature for nanocomposite coatings with different amounts of forsterite was 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite sizes of the prepared coatings were lower than 100 nm. The EDX analysis of hydroxyapatite-forsterite-bioglass, coated 316L SS surface, indicated consisting elements of prepared coatings and the substrate. During immersion in the SBF at pre-determined time intervals, apatite layer was formed and stimulation for apatite formation was increased with increase in forsterite amounts. It seems that hydroxyapatite-forsterite-bioactive glass nanocomposite coatings might be good candidates for biomedical applications.     

Synthesis and characterization of polyamphoteric hydrogel membrane based on chitosan

Polyamphoteric hydrogel membranes were synthesized by graft copolymerization of N‐isopropylacrylamide (NIPAm) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) onto chitosan (CS). The incorporation of poly(NIPAm) (PNIPAm) and poly(AMPS) (PAMPS) into CS was confirmed by FTIR spectroscopy. The swelling behavior of membranes as a function of pH, temperature, and ionic strength was studied. Permeability of solutes through these membranes was investigated at different temperatures. The results showed the dual sensitivity of membranes toward pH and temperature. The formation of the polyelectrolyte complex between CS and PAMPS showed influence on the lower critical solution temperature of PNIPAm. The permeabilities of solutes through these membranes were strongly dependent on the size of solutes, solution temperature, and hydrophilicity of the membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1454–1461, 2004     

Synthesis and characterization of polyethylene-based ionomer nanocomposites

A solvent-free reaction of polyethylene-g-maleic anhydride with a tertiary amino alcohol is used to prepare an ammonium carboxylate polyampholyte (PE-g-PA), whose structure is characterized through spectroscopic comparisons to an appropriate model compound. The introduction of ionic functionality results in substantial increases in melt elasticity and viscosity, as well as a demonstrably improved ability to exfoliate onium ion-exchanged montmorillonite clay (NR₄⁺-MM) and to disperse nanosilica (SiO₂). Physical and rheological analysis of these nanocomposites suggest that in spite of its relatively small surface area and its capacity to engage only in ion-dipole interactions with PE-g-PA, nanosilica provides a better balance of viscoelastic and mechanical properties when compared with onium-ion exchanged montmorillonite.