Cobalt/copper-decorated carbon nanofibers as novel non-precious electrocatalyst for methanol electrooxidation

In this study, Co/Cu-decorated carbon nanofibers are introduced as novel electrocatalyst for methanol oxidation. The introduced nanofibers have been prepared based on graphitization of poly(vinyl alcohol) which has high carbon content compared to many polymer precursors for carbon nanofiber synthesis. Typically, calcination in argon atmosphere of electrospun nanofibers composed of cobalt acetate tetrahydrate, copper acetate monohydrate, and poly(vinyl alcohol) leads to form carbon nanofibers decorated by CoCu nanoparticles. The graphitization of the poly(vinyl alcohol) has been enhanced due to presence of cobalt which acts as effective catalyst. The physicochemical characterization affirmed that the metallic nanoparticles are sheathed by thin crystalline graphite layer. Investigation of the electrocatalytic activity of the introduced nanofibers toward methanol oxidation indicates good performance, as the corresponding onset potential was small compared to many reported materials; 310 mV (vs. Ag/AgCl electrode) and a current density of 12 mA/cm² was obtained. Moreover, due to the graphite shield, good stability was observed. Overall, the introduced study opens new avenue for cheap and stable transition metals-based nanostructures as non-precious catalysts for fuel cell applications.     

One-step fabrication of branched poly(vinyl alcohol) nanofibers by magnetic coaxial electrospinning

Branching has been emerging in 3-D interconnecting building blocks. Branched and hyperbranched poly(vinyl alcohol) (PVA) nanofibers were fabricated by coaxially electrospinning two-liquids under an alternating magnetic field in a facile manner. Both the PVA nanofiber trunks with diameter of 100–200 nm and the PVA nanofiber branches with diameter of 10–30 nm were formed in a single step. The length and the morphology of the branched PVA nanofibers could be controlled through a rational design of the magnetic field. The facile technique may readily be extended to prepare 3-D branched nanofibers from other materials such as various polymers and polymer–ceramic materials. Moreover, the multifunctional and multicomponent materials with branched nanostructure could be expected by using the magnetic coaxial electrospinning technique. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrospun CdS–TiO2 doped carbon nanofibers for visible-light-induced photocatalytic hydrolysis of ammonia borane

CdS/TiO₂ NPs-decorated carbon nanofibers were introduced as a novel photocatalyst working under visible light radiation for the effective hydrolytic dehydrogenation of ammonia borane. Calcination of electrospun nanofiber mats composed of titanium tetraisopropoxide, poly (vinyl pyrrolidone) (PVP), and cadmium acetate dihydrate with a few drops of ammonium sulfide in argon atmosphere at 850 °C led to the production of CdS–TiO₂ decorated carbon nanofibers. As-synthesized nanocomposite exhibited a strong photocatalytic activity for catalytic hydrolysis of ammonia–borane. The favorable electrons-transfer properties, better dispersion, high surface area, and adsorption property are the main features of nanocomposites that exhibit high catalytic efficiency.     

Physicochemical characterization of hydrogels based on polyvinyl alcohol–vinyl acetate blends

Hydrogels made of polyvinyl alcohol–vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure, and dynamic mechanical properties. Hydrogels prepared by blending polyvinyl alcohol–vinyl acetate with either polyacrylic acid or poly(4‐vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid–polyvinyl alcohol–vinyl acetate hydrogels, whereas a porous structure was observed on the freeze‐dried poly(vinyl pyrrolidone)–polyvinyl alcohol–vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol–vinyl acetate alone or polyacrylic acid–polyvinyl alcohol–vinyl acetate blends were thermally treated at high temperatures (i.e., 150°C). Low storage modulus was observed for both poly(vinyl pyrrolidone) and poly(4‐vinyl pyridine)‐containing hydrogels. Temperature dependency of storage modulus from 20 to 60°C was observed only for poly(4‐vinyl pyridine)–polyvinyl alcohol–vinyl acetate hydrogels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3578–3590, 2001     

Graft polymerization of vinyl acetate onto starch. Saponification to starch–g–poly(vinyl alcohol)

Graft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt-60 irradiation of starch-monomer-water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly-(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add-on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add-on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add-on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate-methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40-50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid-modified or hypochlorite-oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid-modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add-on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable physical mixture of starch and poly(vinyl alcohol).     

EMI Shielding Effectiveness of Carbon Nanofiber Filled Poly(vinyl alcohol) Coating Materials

Electromagnetic interference (EMI) shielding on plastic mostly consists of conductive fibers in a polymer matrix. This study describes a route for the fabrication of carbon nanofiber filled poly(vinyl alcohol) (PVA) coating materials. Electrical conductivity of the coating materials ranged from 0.033 to 0.169 S/cm depending on the carbon nanofiber fillers produced from different catalyst compositions and gas types. At the frequency of 850 MHz, the shielding effectiveness of coating materials filled with carbon nanofibers was 0.5–1.6 dB, and the values were improved into 1.6–4.8 dB as the carbon nanofibers were treated at 1 100°C for 1 h.     

Zur Synthese und Funktionalisierung neuer Poly[(silylen)‐2,5‐thiophene]

Treatment of 2,5‐dilithiothiophene with (dimethylamino) methylsilylbis(triflates) gave poly[(dimethylamino‐silylene)‐2,5‐thiophene] 4 in high yield. The amino–silyl bond was cleaved selectively by triflic acid leading to triflate substituted poly[(silylene)‐2,5‐thiophene] 5 . Conversions of this polymers with nucleophiles gave other functionalized derivatives 6 – 9 . Hydrosilylation reaction between silicon–vinyl and silicon–hydrogen derivatives results in polymer networks which may serve as interesting preceramic materials. The structures of the polymers were proven by NMR spectroscopy (²⁹Si, ¹³C, ¹H).     

Preparation of polystyrene/poly(vinyl acetate) nanocomposites with a core–shell structure via emulsifier‐free emulsion polymerization

Polystyrene/poly(vinyl acetate) latex nanoparticles with a core–shell morphology in an emulsifier‐free emulsion polymerization system were prepared with purified styrene and vinyl acetate (VAc) as monomers and 2,2′‐azo bis(2‐amino propane) dihydrochloride (ABA,2HCl) as the initiator and emulsifier. The optimized conditions of polymerization of VAc, on top of the already‐formed polystyrene as a core polymer, with a core–shell morphology were obtained using various parameters such as volume ratio of the first and second stages, type of process, and reaction time. The morphologic structure of the nanoparticles was studied by scanning electron microscopy and transmission electron microscopy. The latex nanoparticles and polymers were characterized by differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2409–2414, 2006     

Au/PANA/PVAc and Au/P(ANA-co-CNTA)/PVAc electrospun nanofibers as tyrosinase immobilization supports

Au/poly anthranilic acid/poly vinyl acetate and Au/poly(anthranilic acid-co-3-carboxy-N-(2-thenylidene)aniline)/poly vinyl acetate nanofibers through electrospinning and their modification with covalent tyrosinase (Ty) immobilization was performed. It was realized by surface activation using N-(3-dimetylaminopropyl)-N-ethylcarbodimide hydrochloride/N-hydroxysuccinimide chemistry. Electrochemical impedance spectroscopy (EIS), FTIR–ATR, Raman spectroscopy, and bicinchoninic acid assay analyses demonstrated that Ty was stably and covalently bonded onto the nanofibers. Increase in surface roughness [atomic force microscopy (AFM)] and the presence of Cu atoms in the nanofiber composition after enzyme immobilization confirmed the Ty immobilization. The charge transfer resistances of the nanofibers decreased due to changes in the nanofiber surfaces after attachment of enzyme.     

Synthesis and characterization of boron doped bismuth–calcium–cobalt oxide nanoceramic powders via polymeric precursor technique

In this study, boron doped calcium stabilized bismuth cobalt oxide nanocrystalline ceramic powders were successfully prepared from aqueous boric acid containing calcium–bismuth–cobalt acetate/poly(vinyl alcohol) hybrid precursor polymer solutions. Then, obtained ceramic powders were characterized via FT-IR, XRD, and SEM techniques. According to X-ray results, fcc and bcc phases coexist in the samples of the nanocrystalline ceramic powders. fcc peaks became sharper and bcc peak decreased with increasing boron content. Structural parameters for face centered cubic structure were calculated using the Scherrer equation. Moreover, dislocation densities and microstrain values were calculated for the nanocrystalline powder samples.     

Poly(acrylonitrile‐co‐vinyl acetate)/Ag composite microspheres: One‐pot fabrication and application as catalyst

Waxberry‐like poly(acrylonitrile‐co‐vinyl acetate)/Ag composite microspheres have been prepared simply and directly via a one‐step self‐assembly approach. The morphology, formation, and catalytic activity of the as‐prepared composite microspheres are further investigated. The difference in the solubility among different segments of poly(acrylonitrile‐co‐vinyl acetate) is the basis of the formation of poly(acrylonitrile‐co‐vinyl acetate) microspheres, while the ? CN groups on the surface of poly(acrylonitrile‐co‐vinyl acetate) microspheres play an important role in the growth process from poly(acrylonitrile‐co‐vinyl acetate) microsphere to poly(acrylonitrile‐co‐vinyl acetate)/Ag composite microsphere. It is found that bulk quantities of composite microspheres with high density of Ag nanoparticles on the surface can be obtained readily by controlling the concentration of AgNO₃. The as‐prepared composite microsphere exhibits excellent catalytic activity on reduction of p‐nitrophenol. This study may shed some light on the self‐assembly of other metal/polymer composite microspheres. POLYM. ENG. SCI., 50:1767–1772, 2010. © 2010 Society of Plastics Engineers     

Study of the effect of rutile/anatase TiO2 nanoparticles synthesized by hydrothermal route in electrospun PVA/TiO2 nanocomposites

Mixed rutile–anatase TiO₂ nanoparticles were synthesized by hydrothermal treatment under acidic conditions and incorporated into poly(vinyl alcohol) (PVA). These nanocomposites were electrospun to produce nanofibers of PVA/TiO₂, which were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The photocatalytic degradation of Rhodamine B and degradation of the polymer by UV‐C lamps were also investigated. The results showed that TiO₂ nanoparticles did not change the morphology and thermal behavior of the nanofiber polymer, but were effective in modifying the UV absorption of PVA without reducing its stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymer Nanocomposites based on Modified ZrO2 NPs and Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) Blend: Optical,Morphological, and Thermal Properties

Nanocomposite films were prepared successfully by simple solution casting method from the blend of poly(vinyl alcohol) and poly(vinyl pyrrolidone) as the polymer matrix and functionalized ZrO₂ nanoparticles as nanofiller. To prevent aggregation and improve the dispersion of nanoparticles into the matrix, ZrO₂ nanoparticles were functionalized with citric acid and ascorbic acid. Then, nanocomposites were fabricated by adding different contents of modified nanoparticles into the poly(vinyl alcohol)–poly(vinyl pyrrolidone) matrix. Thermal stability of the obtained nanocomposite films was improved in comparison to the pure blend. Furthermore, optical property of nanocomposites makes them a potential candidate for ultraviolet shielding material.     

Solubilities of nonvolatile solutes in polymers from molecular thermodynamics

Because there is no simple, general method for measuring solubilities of nonvolatile solutes in a polymer, this work presents a thermodynamic framework for estimating such solubilities from infinite-dilution distribution-coefficient data for aqueous solutions of the solute in equilibrium with the polymer. The experimental infinite-dilution distribution coefficient is related to that calculated from a molecular-thermodynamic model (Flory–Huggins). The three binary Flory parameters are obtained from water–solute and water–polymer data, and from the solute's distribution coefficient. Solubilities of 19 nonvolatile aromatic solutes were estimated in three polymers: ethyl-vinyl acetate copolymer (EVAc) with 33 (EVAc33), 45 (EVAc45) wt. % vinyl acetate content, and poly(vinyl acetate) (PVAc) at 25°C, where most of the solutes are solids. For some of these systems, predicted solubilities are compared with new experimental results. The calculations reported here may be useful for various applications, including the design of membrane processes or drug-delivery systems, and for packaging technology for foods, chemicals, and pharmaceuticals.     

Polymer nanocomposites containing carbon nanotubes and miscible polymer blends based on poly[ethylene‐co‐(acrylic acid)]

Four binary polymer blends containing poly [ethylene‐co‐(acrylic acid)] (PEAA) as one component, and poly(4‐vinyl phenol‐co‐2‐hydroxy ethyl methacrylate) (P4VPh‐co‐2HEMA) or poly(2‐ethyl‐2‐oxazoline) (PEOx) or poly(vinyl acetate‐co‐vinyl alcohol) (PVAc‐co‐VA) or poly (vinylpyrrolidone‐co‐vinyl acetate) (PVP‐co‐VAc) as the other component were prepared and used as a matrix of a series of composite materials. These binary mixtures were either partially or completely miscible within the composition range studied and were characterized by differential scanning calorimetry (DSC) and Fourier transformed infrared spectroscopy (FTIR). Carbon nanotubes (CNTs) were prepared by a thermal treatment of polyester synthesized through the chemical reaction between ethylene glycol and citric acid over an alumina boat. High resolution transmission electron microscopy (HRTEM) was used to characterize the synthesized CNTs. Films of composite materials containing CNTs were obtained after evaporation of the solvent used to prepare solutions of the four types of binary polymer blends. Young's moduli of the composites were obtained by thermomechanical analysis at room temperature. Only one glass transition temperature was detected for several compositions on both binary blends and the composite material matrices. Evidence of hydrogen bond formation was recorded for both miscible blends and composite materials. The degree of crystallinity and Young's moduli of the CNT‐polymer composites increased compared to the single polymer blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Radiation-convertible polymers from norbornenyl derivatives. Crosslinking with ionizing radiation

Vinyl polymers with pendant norbornenyl (bicyclo[2.2.1]heptenyl) groups crosslink rapidly on exposure to ionizing radiation. Analysis (according to Charlesby-Pinner theory) of extraction data from an ethylene–vinyl acetate copolymer and the corresponding ethylene–vinyl norbornenecarboxylate copolymer shows that the unsaturated polymer crosslinks by a chain reaction. At low doses, the kinetic chain length is about 4. Pendant norbornenyl groups accelerate crosslinking of a vinyl alcohol–vinyl acetate–vinyl chloride copolymer and convert poly(vinyl alcohols) and cellulose acetate from degrading to crosslinking polymers. A novel application of the Charlesby-Pinner plot strongly suggests linear dependence of the extent of crosslinking on the norbornenyl group concentration in a series of modified poly(vinyl alcohols). The greater effectiveness of pendant norbornenyl groups, compared to cyclohexenyl groups, demonstrates the importance of the reactivity of the double bond.     

Studies on syntheses and permeabilities of special polymer membranes.: 15. Permeation characteristics of nylon-12 cellulose acetate blends

The permeation characteristics of nylon-12-cellulose acetate polymer blend membranes in the separation of polymers, poly(vinyl alcohols), from their aqueous solutions were investigated under various conditions. The permeation characteristics were influenced markedly by the ratio of nylon-12-cellulose acetate, the feed concentration, the operating pressure and temperature. It was found that the changes of polymer ratio and the concentration of blended polymer were related to the change of microporous structure of the resulting membranes. When the cellulose acetate content was higher a significant compaction of the membrane occurred under pressure. It was found that there was a concentration polarization of poly(vinyl alcohol) molecules on the membrane surface, whose thickness increased with increase in molecular weight of poly(vinyl alcohol) and in feed concentration. The bursting strength of the polymer blend membranes swollen with water increased considerably as the cellulose acetate content in the blended polymer increased.     

Synthesis of CdS nanoparticles dispersed within solutions and polymer films using amphiphilic urethane acrylate chains

In this study, a new process for preparation of CdS/polymer nanocomposite films using a new amphiphilic oligomer chain (Urethane Acrylate Nonionomer: UAN) is presented. UAN chains have hydrophilic polyethylene oxide segments and polypropylene oxide-based hydrophobic segments as part of the same backbone. In addition, these chains also have reactive vinyl groups at their hydrophobic segments. For the preparation of CdS nano-colloid solutions, UAN chains acted as a stabilizer for CdS nanoparticles dispersed in a solvent. For the fabrication of CdS/polymer nanocomposite films, UAN chains in CdS nano-colloid solutions were polymerized through reactions between their vinyl groups, resulting in the formation of CdS nanoparticle dispersed films swollen by the solvent. The nature of the solvent used strongly influenced the size of the CdS nanoparticles, which was confirmed by UV absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher polar solvents such as DMAc and methanol, which can be explained by the higher solubility of UAN chains and the more effective dissociation and stabilization of cadmium salts and CdS nanoparticles by UAN chains in the polar solvent.     

In situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through an electrospinning process

Iron oxide nanoparticle coated poly(ethylene oxide) nanofibers as organic–inorganic hybrids with 200–400‐nm diameters were prepared by the in situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions in a gaseous ammonia atmosphere. Transmission electron microscopy analysis proved the presence of iron oxide nanoparticles on the polymer nanofibers. The thermal properties of the nanofiber mat were also studied with differential scanning calorimetry and thermogravimetric analysis techniques. X‐ray diffraction showed that the formed iron oxide nanoparticles were maghemite nanoparticles. The results were compared with those of the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions and a pure poly(ethylene oxide) solution in an air atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Semi- and fully interpenetrating polymer networks based on polyurethane-polyacrylate systems. IX. Properties of an isomerically related interpenetrating network

Two polyurethane–poly(vinyl acetate) interpenetrating polymer networks of differing composition were synthesized and certain physical properties investigated. The results are compared with semi-1-interpenetrating polymer networks of the same system as well as with, where appropriate, polyurethane-poly(methyl acrylate) interpenetrating polymer networks. Dynamic mechanical analysis clearly indicated phase separation for both compositions. The poly(vinyl acetate) glass transition showed a shift to lower temperatures accompanied by a shift to higher temperatures of the polyurethane transition. Such shifts indicate a certain extent of mixing. Electron microscopy confirmed phase separation and for a material with 20% by weight of polyurethane indicated that both components are continuous. This latter material also had a higher tensile strength and elongation at break than the corresponding poly(vinyl acetate) homopolymer. At 60% by weight of polyurethane the stress-strain characteristics are those of a reinforced rubber. Certain modulus–composition theories, and, also, sonic velocity measurements were consistent with these morphological conclusions.