Graphite nanofibers prepared from catalytic graphitization of electrospun poly(vinylidene fluoride) nanofibers and their hydrogen storage capacity

Electrospun poly(vinylidene fluoride) nanofibers were carbonized with iron(III) acetylacetonate to induce catalytic graphitization within the temperature range 800–1800 °C. Carbonization in the presence of the catalyst produced graphite nanofibers (GNFs). Their structural properties and morphology were investigated. GNFs with a high surface area of 377–473 m²/g showed the typical Type II containing mesopore in nitrogen adsorption–desorption isotherms. The hydrogen storage capacity of these GNFs was evaluated by the gravimetric method using a magnetic suspension balance (MSB) at room temperature and about 80 bar. The hydrogen storage capacity was 0.11–0.18 wt.%. The effective pore size for hydrogen storage compared to the diameter of the hydrogen molecule is discussed.     

Elasticity of poly(acrylamide) gel beads

Summary The elastic behavior of swollen ionic poly(acrylamide) (PAAm) gel beads was investigated as a function of the bead diameter. For this purpose, an experimental setup was designed to measure the modulus of hydrogel beads. An inverse suspension polymerization technique was used to obtain spherical beads of sizes 3 to 11 mm. It was observed that the effective crosslink density of PAAm gel beads produced in the same synthesis batch increases with increasing bead diameter, which was attributed to the inverse suspension polymerization condition. Received: 6 November 2002/Revised version: 4 April 2003/ Accepted: 4 April 2003 Correspondence to Oguz Okay     

High strength poly(acrylamide)-clay hydrogels

A series of polyacrylamide nanocomposite hydrogels were synthesized by in situ free radical polymerization of acrylamide (AAm) with ethylene glycol dimethacrylate (EGDMA) as a crosslinker in the presence of sodium montmorillonite (NaMMT) and organically modified montmorillonite (OrgMMT) clays. Modification of MMT was carried out with a quaternary salt of coco amine as intercalant having a styryl group whose contribution to both polymerization and crosslinking reactions via its reactive double bond was confirmed by solid state NMR. Exfoliation success was checked with X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques whereas mechanical performance was followed with uniaxial compression experiment. It has been found that exfoliated PAAm nanocomposites having 0.5% OrgMMT had both the maximum equilibrium swelling in water and compression strength as well as improved thermal stability due to the special and beneficial morphology observed via scanning electron microscopy (SEM).     

Poly(hydroxamic acid) hydrogels from poly(acrylamide): preparation and characterization

Summary Poly(hydroxamic acid) (PHA) hydrogels from crosslinked poly(acrylamide) (PAAm) hydrogels containing different type crosslinkers such as such as N, N'-methylene bisacrylamide (N) and ethyleneglycol dimethacrylate (E). The effect of crosslinkers on some physical properties was investigated. The structure of hydrogels was characterized spectroscopically and thermally. The swelling parameters of PHA in distilled water, such as percent equilibrium swelling (S_eq%), initial swelling rate (r_o), maximum equilibrium swelling (S_max), diffusional exponent (n), network parameter (k) and diffusion coefficient (D) were calculated. It has been found that the ionogenity of PHA and the structure of the used crosslinkers during the synthesis have been effective on the swelling behaviour of the hydrogels. Received: 12 February 2001 / Revised version: 30 June 2001 / Accepted: 11 July 2001     

Swelling kinetics of poly(acrylamide)/poly(mono-n-alkyl itaconates) hydrogels

Hydrogels of mono-n-alkyl itaconate/N-acrylamide have been synthesised. The swelling process at three different pH values (acid, neutral and basic) has been studied. The experimental data indicate that our hydrogels follow second-order swelling kinetics. According to this, the kinetic constant, K_∞, and the swelling capacity at equilibrium, W_∞, have been calculated. The influence of the solvent pH and the molar mass of the mono-n-alkyl itaconate monomeric unit has been analysed. It seems that the general balance between the hydrogen bonding and the hydrophobic interactions regulates the swelling process of these hydrogels.     

Adsorption properties of carbon prepared from poly(tetrafluoroethylene)

The adsorption equilibria of benzene were studied on carbon samples prepared by the electrochemical reduction of poly(tetrafluoroethylene) between 10 and 80°C. Adsorption isotherms and isosteric heats of adsorption of benzene were compared with the data obtained for standard activated carbon and for graphitized carbon black. The modified Freundlich equation was used to express adsorption isotherms of benzene on the studied samples. The parameters of the equation gave information on the structure of the samples. This information is consistent with the results of the radial distribution of the electron density and wide-angle X-ray scattering carried out earlier.     

Water-swellable rubbers containing powdery poly(acrylamide) hydrogel

Hydrophilic composite materials were prepared by combining powdery poly(acrylamide) hydrogel with various technical rubbers (natural rubber, chlorobutyl rubber, EPDM rubber). The dependence of the quality of the dispersions of powdery hydrogel in rubbers on the method of dispersion was studied and properties (swelling capacity in water, mechanical characteristics) of the composites were measured. The natural rubber/hydrogel composites showed the best swellability (>80 vol.-%). The mechanical properties of the composites are comparable to those of the unmodified rubbers, both in the dry and water-swollen state.     

聚（苯乙烯－丙烯酰胺）三氯化钕配合物的制备

合成了聚（苯乙烯－丙烯酰胺）三氯化钕配合物（ＳＡＡ·ＮｄＣｌ３），高分子链上的功能团是通过羧基氧原子与稀土离子配位的。     

High strength poly(meth)acrylamide copolymer hydrogels

Summary The hydrogels described here are copolymers of acrylamide and methacrylamide highly cross-linked with piperazine diacrylamide or 4, 7, 10-trioxa-1, 13-tridecanediamine diacrylamide by radical polymerisation in highly concentrated aqueous and aqueous gelatin solutions. The hydrogels were characterised by their compressive strength, refractive indices, densities, ‘free’ water contents and degree of swelling. The hydrogels cross-linked with piperazine diacrylamide gave strong glassy hydrogels, which we have termed “hydroglasses”. Cross-linking with 4, 7, 10-trioxa-1, 13-tridecanediamine diacrylamide, which contains a long flexible spacer, did not result in a more elastic gel. Polymerisation in an aqueous gelatin solution improved the mechanical properties of the gel enormously.     

Reactive electrospinning of poly(vinyl alcohol) nanofibers

We aim to couple the electrospinning in‐line with solution chemistry to fabricate novel crosslinked polymer nanofibers. Poly(vinyl alcohol) (PVA) was used as a model polymer due to its high amount of hydroxyl groups. To obtain ideal parameters for electrospinning, pure PVA was explored primarily. To gain crosslinked fibers, PVA was first crosslinked partially with glutaraldehyde (GA) followed by transferring this precursor to a long hot tube which was used as reactor and then electrospun right before gelation. The preheating time and tube‐passing time were determined with viscometer and rheometer. The reactive as‐spun fibers could maintain their original morphology after water immersion due to their high crosslinking degree. The thermal stability and mechanical property of reactive as‐spun fibers were improved drastically compared with pure and GA vapor crosslinked PVA fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Infrared study of the complexation of poly(acrylic acid) with poly(acrylamide)

Infrared spectroscopy was used to study the interpolymer complexation of poly(acrylic acid) with polyacrylamide. The spectrum of the interpolymer complex showed characteristic absorption bands which are different from those of the spectra of the individual components, particularly in the O H and N H stretching vibration regions. The effects of ionic strength and poly(acrylic acid) weight fractions on the spectral features of the complex were investigated. It was found that hydrogen bonding is the primary mechanism of interaction between the two polymers. © 1996 John Wiley & Sons, Inc.     

Interpolymer complexes of poly(acrylamide) and poly(N-isopropylacrylamide) with poly(acrylic acid): a comparative study

The interpolymer complexation, through successive hydrogen bonding, between poly(acrylamide) (PAAm) and poly(N-isopropylacrylamide) (PNiPAAm) with poly(acrylic acid) (PAA) in aqueous solution has been viscometrically and potentiometrically investigated. The stoichiometry of the complexes formed was determined. By comparing the strength of the two complexes the very important contribution of the hydrophobic interaction in their formation has been indicated.     

Microwave accelerated synthesis and characterization of poly(acrylamide)

Poly(acrylamide) (PAM) was efficiently synthesized under microwave (MW) irradiation using catalytic amount of potassium persulfate. The synthesis does not require any inert atmosphere and could be accomplished in very short time. Microwave power, exposure time, concentration of persulfate, and concentration of the acrylamide were varied to optimize the polymerization in terms of the % conversion (%C). The maximum %C that could be achieved was in 98.5%. The average molecular weight of the synthesized PAM samples ranged from 4.11 × 10⁴ to 1.30 × 10⁵, depending upon the MW power used for their synthesis. The representative PAM was characterized by Fourier transform‐infrared, SEM, and X‐ray diffraction studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3702–3707, 2007     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fluorescent poly(p-phenylene vinylene)/poly(ethylene oxide) nanofibers obtained by electrospinning

Poly(p-phenylene vinylene) (PPV)/poly(ethylene oxide) (PEO) hybrid nanofibers were prepared by electrospinning a composite solution of PPV precursor/PEO in a mixture of ethanol and water, followed by thermal conversion. The precursor/PEO composite solutions were successfully electrospun into nanofibers with diverse helical, helical and linear, and helical bead-on-string morphologies by controlling the amount of aqueous PEO solution in a composite solution. Moreover, adding aqueous PEO solution to a precursor ethanol solution decreased the diameters of the fibers. The experimental data suggest that the viscosity, conductivity, and surface tension of the electrospinning solution are the main factors that influence the morphology of the fibers. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) investigations indicated that the PPV precursor reacts with PEO during thermal conversion. Ultraviolet–visible (UV-vis) and photoluminescence (PL) spectra of the PPV-PEO nanofibers exhibited appreciable blue shifts with the addition of PEO, which made it possible to fabricate nanofibers with fluorescence ranging from yellow-green to blue. These highly fluorescent PPV/PEO nanofibers with various morphologies are potentially interesting for many applications, such as micro- and nanooptoelectronic devices and systems.     

电纺制备苯乙烯甲基丙烯酸共聚物单轴定向纳米纤维

采用无皂乳液法合成了带有羧基的苯乙烯-甲基丙烯酸共聚物,并利用静电纺丝技术,得到了不同形貌的直径约为800nm的纳米纤维。同时通过对传统的平面导体收集装置的改进,得到了大面积、单轴定向的功能纳米纤维。     

Electrospinning of cyclodextrin functionalized poly(methyl methacrylate) (PMMA) nanofibers

Cyclodextrin functionalized PMMA nanofibers (PMMA/CD) were successfully produced by electrospinning technique with the goal to develop functional nanowebs. Bead-free uniform electrospun PMMA/CD nanofibers were obtained from a homogeneous solution of CDs and PMMA in dimethylformamide (DMF) using three different types of CDs, α-CD, β-CD and γ-CD. The electrospinning conditions were optimized in order to form bead-free PMMA/CD nanofibers by varying the concentrations of PMMA and CDs in the solutions. The concentration of CDs was varied from 5% up to 50% w/w, with respect to the PMMA matrix. We find that the presence of the CDs in the PMMA solutions facilitates the electrospinning of bead-free nanofibers from the lower polymer concentrations and this behavior is attributed to the high conductivity and viscosity of the PMMA/CD solutions. The X-ray diffraction (XRD) spectra of PMMA/CD nanowebs did not show any significant diffraction peaks indicating that the CD molecules are homogeneously distributed within the PMMA matrix and does not form any phase separated crystalline aggregates. Furthermore, attenuated total reflection Fourier transform infrared (ATR-FTIR) studies elucidate that some CD molecules are located on the surface of the nanowebs. This suggests that these CD functionalized nanowebs may have the potential to be used as molecular filters and/or nanofilters for waste treatment purposes.     

Thermo-responsive nanocarrier based on poly(N-isopropylacrylamide) serving as a smart doxorubicin delivery system

Iranian Polymer Journal - Smart temperature- and pH-responsive nanocarriers could be considered as potent vehicle in drug delivery systems. By this means, a thermo-responsive polymeric nanocarrier...     

Biaxially oriented films prepared from poly(vinyl chloride)/poly(methyl methacrylate co imide) blends

A study was conducted of blends of poly(vinyl chloride) (PVC) with a poly(methyl methacrylate co imide). The latter polymer was found to be miscible in PVC and to raise the glass transition temperature of the blend. Blends of all compositions could be oriented, but the processing temperature increased in proportion with T_g. For a given blend composition, orientation increased with increasing stretch ratio and strain rate and with decreasing stretch temperature. Increasing copolyimide content and increasing orientation generally lead to improved mechanical properties, though the blends containing high levels of copolyimide exhibited low ductilities.     

Characterization of electrospun poly(N-isopropyl acrylamide) fibers

Poly(N-isopropyl acrylamide) (pNIPAM) is an interesting material in that it shows a thermoresponsive behavior around 32 °C in aqueous solutions. This behavior mimics that of many proteins in solution and as a result, many researchers have studied pNIPAM as a model for protein behavior. Yet, little is known about the processability of pNIPAM into three-dimensional matrices and whether such processing affects polymer conformation. In this work, 3D fibrous mats of pNIPAM were prepared by electrospinning from three different solvents and the resulting morphologies evaluated. Additionally, electrospun pNIPAM was evaluated with polarized Raman and infrared spectroscopies and compared against the spectra of the bulk material. It was found that the electrospinning process did not alter the polymer structure or morphology.