X-ray diffraction and X-ray photoelectron spectroscopy studies of Ni-P deposited onto carbon fiber surfaces: impact properties of a carbon-fiber-reinforced matrix

In this work, the Ni-P coating on carbon fiber surfaces was carried out in order to improve the impact resistance of carbon fibers-reinforced epoxy matrix composites. The fiber surfaces and the fracture behaviors of composites were measured in terms of X-ray diffraction spectrometry (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), and falling weight impact testing. From the XRD and XPS measurements, it was observed that Ni-P coating of carbon fibers led to an increase in two phases, i.e., microcrystalline and amorphous, mainly due to the increase of NiP(2), Ni(3)P, and Ni metal. Energy adsorbed by composites through the various fracture mechanisms was seen to be the characteristic distinguishing between nontreated and treated fiber-reinforced composite systems. The Ni-P alloy technique to improve the impact resistance of the composites was shown to be the modification of fiber-epoxy resin interfaces.     

Photochemical grafting of polysulfobetaine onto polyethylene and polystyrene surfaces and investigation of long‐term stability of the polysulfobetaine layer in seawater

Low‐density polyethylene (LDPE) and polystyrene (PS) films with hydrophilic surface were prepared by photochemical grafting of sulfobetaine‐based copolymer containing photolabile moiety, and long‐term stability of the hydrophilic nature of the surfaces in seawater was proved. The sulfobetaine‐based copolymer was prepared by copolymerization of N,N‐dimethyl‐N‐(3‐(methacryloylamino)propyl)‐N‐(3‐sulfopropyl) ammonium betaine with 2 or 5 mol% of N‐methacryloyl‐4‐azidoaniline, and the resulted polymers were grafted onto the plasma pretreated LDPE and PS films. The contact angle measurements were used to prove the modification as well as to follow the changes in the hydrophilicity during storage at room temperature under air atmosphere as well as in seawater at 32°C. The stability of the polymer layer was confirmed also by FTIR and AFM. Polysulfobetaine‐modified LDPE and PS surfaces exhibited significantly higher long‐term hydrophilicity compared with only plasma treated LDPE and PS surfaces.     

Electrochemical grafting of an aryl fluorosulfonimide electrolyte onto glassy carbon

Robust bonded layers of an aromatic fluorosulfonimide electrolyte were created on glassy carbon disk and plate electrodes by electroreduction of a new fluorosulfonimide aryl diazonium zwitterion. Formation of the bonded layer was confirmed by XPS of the modified surfaces and also by the effect of the bound layer on reduction/oxidation of redox-active probe molecules. Surface coverage in the monolayer range was achieved. Counterions for as-formed layers were initially tetra-alkylammonium ions from the coating electrolyte but could subsequently be exchanged for other cations by exposure to salt solutions. The bonded layers are very stable with respect to treatment with solvents (water and/or acetonitrile), dry heat (120 degrees C), and hot acid (triflic acid, 80 degrees C, neat and containing 50 wt % water); however, they are unstable with respect to electro-oxidative scanning in aqueous electrolyte solutions.     

Plasma modification of polypropylene surfaces and grafting copolymerization of styrene onto polypropylene

The surface of polypropylene(iPP) is modified with glow discharge plasma of Ar,so that the modified surfaces of iPP films are obtained.The studies of scanning electron microscopy(SEM) show the surface etching pattern of iPP films. The chemical structures of iPP films are confirmed by X-ray photoelectron spectroscopy(XPS) and Fourier transform infrared(FTIR) spectroscopy.The wetting properties of modified surfaces of iPP films are characterized by contact angle, and the free energy of surfaces is calculated.The free radical of modification surfaces of iPP is measured by chemical method.The surfaces of iPP are achieved with Ar plasma treatment followed by grafting copolymerization with styrene(St) in St.The grafting polymer of St onto iPP is characterized by FTIR.The grafting rate is dependent on plasma exposure time and discharge voltage.The studies show that homopolymerization of St is undergone at the same time during the grafting-copolymerization of St onto iPP.     

Irradiation‐induced grafting of acrylonitrile onto activated carbon fiber

Viscose‐based activated carbon fiber (VACF) was modified with acrylonitrile (AN) by γ‐irradiation‐induced grafting polymerization. Effects of the grafting conditions, such as concentrations of AN and divinylbenzene (DVB), pH value, and solvent on the grafting process were studied. The physicochemical properties of the fibers were characterized. The results show that AN can be effectively grafted onto the surface of VACF with the addition of DVB. The grafting yield is higher than 12% according to thermogravimetric (TG) analysis. The study shows that DVB can improve the grafting degree of AN in the form of grafting chains or agglomerate materials. After grafting modification, VACF shows a small decrease in the specific surface area. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigations into the mechanism of adsorption of carbon nanotubes onto aminopropylsiloxane functionalized surfaces

The factors that control carbon nanotube (CNT) adsorption onto aminopropyl siloxane (APS)-derivatized surfaces were investigated using two distinct types of well-characterized films with significant differences in their detailed structures. Both types of APS films showed a marked increase in CNT adsorption relative to untreated SiO2 surfaces but differed in the amount of CNTs adsorbed. To gain insight into the factors governing adsorption, the surface coverage of the CNTs was monitored as a function of the pH during the deposition, the surfactant used to suspend the CNTs, and the type and amount of salt added to the deposition solution. The adsorption is shown to be governed by electrostatic and VDW forces. In the case of complimentarily charged surfaces, the adsorption is proposed to occur through an ion exchange mechanism.     

Chemically grafting carbon nanotubes onto carbon fibers for enhancing interfacial strength in carbon fiber/HDPE composites

We propose a novel method to uniformly graft high‐density carbon nanotubes (CNTs) onto carbon fiber (CF) by using coupling agents. Coupling agents can supply much more active groups, which is beneficial for grafting high‐density CNTs onto CF surface. After CNT grafting treatment, there are still substantial amounts of reactive groups, which can further react with various types of molecules to meet different requirements. To create chemical bonding between CF and high‐density polyethylene, CF‐CNT was further grafted get reinforcement. The interfacial adhesion of the resulting composites showed a dramatic improvement.     

Photochemical grafting and activation of organic layers on glassy carbon and pyrolyzed photoresist films

Organic films have been grafted to polished glassy carbon (GC) and as-prepared pyrolyzed photoresist film (PPF) by photolysis of alkenes and an alkyne. The alkene or alkyne is spin-coated onto the carbon surface and photolyzed in air at 254 nm. Characterization by water contact angle measurements, depth profiling and surface roughness measurements using atomic force microscopy (AFM), and electrochemistry reveal that for most modifiers a loosely packed monolayer is grafted to the surface. Grafted layers of 1-decene were further reacted by drop-coating with oxalyl chloride and photolyzing at 254 nm in air. The procedure adds acid chloride groups to the film. Amines were attached to these films via amide bond formation, and were characterized by electrochemistry and assembly of citrate-capped gold nanoparticles. Amines were also coupled to photografted 1-undecylenic acid layers and to carboxyphenyl layers prepared by electroreduction of the corresponding diazonium salt. Quantitative analysis using electrochemistry established that the highest concentration of amines was attached to the oxalyl chloride treated film, and that a higher concentration of amines was attached via reaction with the photografted 1-undecylenic acid layer than the electrografted carboxyphenyl layer. Thus photografting and photoreaction with oxalyl chloride are simple methods for generating amine-reactive tethers on GC and PPF surfaces.     

Study of the adsorption of a hydrophobic peptide onto carbon surfaces by capacitance measurements

The adsorption of a hydrophobic peptide (β-CN (193–209)) onto glassy carbon and a carbon support of membrane was studied by double-layer capacitance measurements using electrochemical impedance spectroscopy (SIE). The kinetics of adsorption was investigated by recording the changes that occurred in the double-layer capacitance after adding the peptide. The change in capacitance was interpreted in terms of the number of close-contact areas between the peptide and the surface. A two-consecutive reaction model was used to describe peptide adsorption. The first step was attributed to the adsorption reaction itself and the second to a change in the conformation of the adsorbed peptide molecules. The corresponding theoretical equation of the variation of capacitance with time fits our results. Moreover, it allowed determination of the time constants for both reactions and three double-layer capacitances: the bare surface and the surfaces covered with monolayers of the peptide in states 1 and 2. For glassy carbon, the activation energies are 4.7 and 3.5 kJ mol⁻¹ for the first and second step of the reaction and the reaction orders are 0.64 and 0.35, respectively. These values are different for each step. This confirms the model of two separate reactions to describe adsorption. The first step comprises two elementary mechanisms. The first may correspond to the adsorption of the peptide onto the surface. The second may be consistent with a modification of the adsorbed molecules induced by the adsorption of other molecules over them. The second step of the process requires the contribution of peptides of the solution for it to occur. The changes in the double-layer capacitance depend on the peptide bulk concentration. This suggests that the peptide adsorbs in a different conformation depending on its bulk concentration. Peptide polymerisation could be responsible for this phenomenon.     

Formation of CdSe nanocrystals onto oxidized, ozonized single-walled carbon nanotube surfaces

We present the in situ formation of crystalline CdSe quantum dots on the surfaces of oxidized, ozonized single-walled carbon nanotubes, which is a rational synthetic route to the synthesis of complex hierarchical assemblies.     

Grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticle and carbon black surfaces

The surface grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticles and carbon black was investigated. The grafting of hyperbranched cyclotriphosphazene polymer onto these surfaces was achieved by the repeated reactions of hexachlorocyclotriphosphazene with hexamethylenediamine from surface amino groups and sodium carboxylate groups, respectively. The percentage of grafting onto silica and carbon black surfaces exceeded 760 and 390%, respectively. However, it proved difficult to achieve the theoretical growth of cyclotriphosphazene polymer from these surfaces because of steric hindrance. The introduction of sulfonic acid groups was successfully achieved by the reaction of terminal chlorophosphazene groups of the hyperbranched polymer‐grafted silica and carbon black with sulfanilic acid. The content of sulfonic acid groups introduced onto silica and carbon black surfaces was 4.98 mmol/g and 5.70 mmol/g, respectively. The sulfonated cyclotriphosphazene polymer‐grafted carbon black was extremely hydrophilic, yielding stable colloidal dispersions in polar solvents. The sulfonated cyclotriphosphazene polymer‐grafted silica and carbon black showed ionic conductivity, with the conductance increasing exponentially with increasing relative humidity and temperature. This study may offer important leads in the application of silica nanoparticles and carbon black in polymeric membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4218–4226, 2008     

Photochemical grafting of diazonium salts on metals

4-Nitrobenzenediazonium may be photochemically grafted onto gold, copper and iron under visible and UV light. Thin nanometre layers are obtained and characterized by IRRAS, electrochemistry and ellipsometry.     

Polymer grafting onto carbon black by use of TEMPO-terminated polystyrene with controlled molecular weight

The grafting of polystyrene with controlled molecular weight and narrow molecular weight distribution onto the carbon black surface through the trapping of polymer radicals formed by the thermal dissociation of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-terminated polystyrene (PSt-TEMPO) by the carbon black surface was investigated. PSt-TEMPO was prepared by living radical polymerization of St with the benzoyl peroxide/TEMPO system. When PSt having no terminal TEMPO moiety was heated with carbon black, no grafting of PSt onto the surface was observed. On the contrary, by the heating of PSt-TEMPO with carbon black in m-xylene at 125°C, PSt with controlled molecular weight and narrow molecular weight distribution was grafted onto the surface: the percentage grafting of PSt (M_n = 3.2 × 10³;M_w/M_n = 1.07) onto furnace black was determined to be 16.0%. On the basis of the above results, it is concluded that PSt radicals formed by the thermal dissociation of the C ON bond between PSt and TEMPO are trapped by polycondensed aromatic rings of carbon black. The mole number of grafted PSt chains on the carbon black surface decreased with increasing molecular weight of PSt-TEMPO. PSt-grafted carbon black gave a stable colloidal dispersion in THF. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3165–3172, 1998     

Radical grafting of carbon surfaces with alkylic groups by mediated oxidation of carboxylates

The mediated oxidation of tetrabutylammonium acetate and 4-nitrophenylacetate was carried out in acetonitrile on glassy carbon electrodes. It is discussed that direct oxidation of aliphatic carboxylates, which give rise to a carbocationic chemistry, cannot induce covalent grafting of the carbon surface, however surface grafting is possible by using ferrocene derivatives as electron transfer mediators. Density functional theory has been used to model a radical grafting involving methyl groups. In addition semiempirical calculations have been performed for 4-nitrobenzyl additions, and a new anchoring pattern, is proposed. Coverage factors have been calculated for both kinds of radicals. Both, experimental and theoretical results support the covalent attachment of methyl groups on the carbon surface and the formation of a highly compact monolayer which does not allow the permeation of reversible redox molecules as small as the molecular oxygen.     

Kinetics of grafting acrylonitrile onto starch

Acrylonitrile (AN) was graft copolymerized onto gelatinized and granular wheat starch in aqueous media in the presence of ceric ammonium nitrate initiator at 91-364 anhydroglucose units (AGU) per cerium (IV) and at 1.08-4.33 AN to AGU ratios. Molecular weights and dispersities of polyacrylonitrile side chains were determined by gel-permeation chromatography. Conversion-time plots of AN polymerizations in both gelatinized and granular starch systems show characteristics common to heterogeneous polymerizations that could be explained on the basis of buried polymer radicals. The rates of polymerizations were directly related to the square root of the corrected cerium(IV) concentration and to the 1.3 power of the AN concentration. Graft copolymerization of AN onto starch, at least during initial stages, is not suitably explained by a kinetic scheme involving termination by polymer radical with cerium(IV) ion.     

Studies on the grafting of acrylonitrile-co-styrene onto casein

Graft copolymerization of acrylonitrile and styrene mixture was performed on casein in aqueous medium at pH 7.8 using potassium peroxydisulphate as initiator. The effects of monomer concentration, initiator concentration and temperature were investigated. The individual polymers were isolated by Soxhlet extraction and characterized by i.r. spectroscopy and thermogravimetric analysis.     

Direct covalent grafting of conjugated molecules onto Si, GaAs, and Pd surfaces from aryldiazonium salts

Using aryldiazonium salts that are air-stable and easily synthesized, we describe here a one-step, room-temperature route to direct covalent bonds between pi-conjugated organic molecules on three material surfaces: Si, GaAs, and Pd. The Si can be in the form of single crystal Si including heavily doped p-type Si, intrinsic Si, heavily doped n-type Si, on Si(111) and Si(100), and on n-type polycrystalline Si. The formation of the aryl-metal or aryl-semiconductor bond attachments was confirmed by corroborating evidence from ellipsometry, reflectance FTIR, XPS, cyclic voltammetry, and AFM analyses of the surface-grafted monolayers. A data-encompassing explanation for the mechanism suggests a diazonium activation by reduction at the open circuit potential, with aryl radical secondary products bonding to the surface. The synthetic details are included for preparing the surface-grafted monolayers and the precursor diazonium salts. This spontaneous diazonium activation reaction offers an attractive route to highly passivating, robust monolayers and multilayers on many surfaces that allow for strong bonds between carbon and surface atoms with molecular species that are near perpendicular to the surface.     

Polymer-clay nanocomposites: Free-radical grafting of polyacrylamide onto organophilic montmorillonite

This paper is an account of the experiments on grafting polyacrylamide onto organophilic montmorillonite. Cloisite 20A was reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety. Since the reaction liberates HCl, it was performed in the presence of sodium hydrogencarbonate to prevent the exchange of quaternary alkyl ammonium cations with H⁺ ions. Only the silanol groups on the edge of the clay react with vinyltrichlorosilane. The product maintained the same basal spacing as the precursor. The radical polymerization of the product with acrylamide as a vinyl monomer leads to chemical grafting of polyacrylamide onto montmorillonite surface. The homopolymer formed during polymerization was Soxhelt extracted from the grafted organoclay. Chemical grafting of the polymer onto Cloisite 20A was confirmed by IR spectroscopy. The interlayer and surface changes of the clay in the prepared nanocomposite materials and the grafted nano-particles were studied by XRD and SEM. Intercalated nanocomposites were obtained for clay contents of 3-7% and agglomeration occurred at higher clay loadings. The nanocomposites were studied by thermogravimertic analysis (TGA) and dynamic mechanical analysis (DMTA).     

Photoinitiated grafting of maleic anhydride onto polypropylene

The photoinitiated grafting of maleic anhydride (MAH) onto polypropylene with the use of benzophenone (BP) as the initiator has been investigated. In comparison with the process of thermally initiated grafting with peroxide as the initiator, photoinitiated grafting affords a higher grafting efficiency. The efficient photografting sensitized by BP can be explained by two possible mechanistic processes: the sensitization of the formation of the excited triplet state of MAH by BP and electron transfer followed by proton transfer between MAH and the benzopinacol radical, which may operate together. In the former case, the generated MAH excited triplet state abstracts a hydrogen from the polymer substrate to initiate grafting. A rate constant of 3.6 × 10⁹ M ^?1 s ^?1 has been determined by laser flash photolysis for the process of quenching the excited triplet state of BP with ground‐state MAH. In comparison, the rate constant for the quenching of the excited triplet state of BP by hydrogen abstraction has been determined to be 4.1 × 10⁵ M ^?1 s ^?1. In a study of photografting using a model compound, 2,4‐dimethylpentane, as a small‐molecule analogue of polypropylene, the loss of BP was significantly reduced upon the addition of MAH, and this is consistent with the proposed mechanistic processes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1953–1962, 2004