Association behaviors of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone)-grafted fullerenes in aqueous solution

Poly(N-vinylpyrrolidone) (PVP)-grafted fullerenes (PVP-C₆₀ and PVP-C₇₀) were synthesized by iniferter polymerization in order to fabricate water-soluble fullerene containing micelles. PVP-C₆₀ formed micelles with hydrodynamic diameters ranging from 15 to 33 nm. The solubilization of fullerene molecules into the core of the PVP-C₆₀ micelles was also found to control the size of the micelles. By increasing the amount of added fullerene, we gradually increased the micelle size before drastically increasing it to that of 200 nm in hydrodynamic diameter. The drastic change occurred at a critical value of the added C₆₀/PVP monomer ratio, almost independently of the molecular weight of PVP.     

Static and dynamic light scattering study of strong intermolecular interactions in aqueous solutions of PVP/C60 complexes

The investigations of the dilute aqueous solutions of polyvinylpyrrolidone/fullerene (PVP/C₆₀) complexes by static (SLS) and dynamic (DLS) light scattering showed that strong intermolecular interactions, effective on the distances of about 45-50 nm, take place in the solutions. Two concentration ranges are well distinguished in these solutions. Above a critical concentration (c_cr) the fluctuations in the solutions are hindered and only one, diffusive, mode is observed in DLS experiments. Upon dilution (c<c_cr) this unified structure divides into large fragments (domains) and the slow mode attributed to long-range concentration fluctuations, gradually appears. The angular and concentration dependencies of the diffusion coefficient of the slow mode indicate the existence of strong intermolecular interactions.     

Poly(vinyl pyrrolidone)—C70 complexes in aqueous solutions

Aqueous solutions of poly(vinyl pyrrolidone)-fullerene complexes (PVP-C₇₀) have been studied using static and dynamic light scattering methods. Two diffusive processes were detected. The slow diffusion was interpreted as dynamics of large intermolecular PVP-C₇₀ complexes while the fast diffusion was associated with the presence of individual PVP molecules in solution. It was also shown that the molecular weights and dimensions of PVP-C₇₀ complexes are smaller than for PVP-C₆₀ by a factor of 2.5-3. In aqueous solutions of PVP-C₇₀ complex the depolarization and dissymmetry of scattered light were observed in contrast to PVP-C₆₀ solutions. It reveals the existence of anisotropic structures in PVP-C₇₀ solutions. Intermolecular interactions within PVP-C₇₀ complexes are weak and a hydrodynamic field can destroy complexes.     

Polymeric fullerene oxide (fullerene ozopolymers) produced by prolonged ozonation of C60 and C70 fullerenes

The prolonged ozonation of C₆₀ and C₇₀ fullerene produces light brown to brown amorphous solids which are insoluble in chlorinated and hydrocarbon solvents but which are readily soluble in water, acetone and ethanol where they give dark-brown solutions. The polymeric and polyelectrolytic nature of these solids has been shown by viscosimetric and cryoscopic measurements. Due to the polymeric nature the solids have been called ‘ozopolymers’. The reactivity and the ozone uptake have been measured quantitatively during the ozonation of C₆₀ and C₇₀ fullerene in CCl₄. Three different C₆₀ ozopolymer samples have been produced at different degrees of ozonation: at O₃/C₆₀ molar ratio of 8, 14 and 26. The C₇₀ ozopolymer has been produced at an O₃/C₇₀ molar ratio of 30. All the samples have been studied by FT-IR spectroscopy and the C₆₀ ozopolymers have been easily reduced by the action of Zn dust and acetic acid or by the action of H₂S and studied by FT-IR. The action of oxidizing agents has been studied as well. C₆₀ ozopolymer is a polyelectrolyte rich in carboxyl groups and for this reason it possesses a high metal binding capacity similar to that of humic acids. The thermal stability of C₆₀ ozopolymer and its reduced derivatives as well as the thermal stability of C₇₀ ozopolymer has been checked by thermogravimetric analysis in nitrogen and air flow. Finally, the electrical conductivity of C₆₀ ozopolymer was found to be σ=2.8×10⁻⁸ S/cm which is three orders of magnitude lower than that of pure C₆₀.     

Template-free fabrication of fullerene (C60, C70) nanometer-sized hollow spheres under solvothermal conditions

Fullerene (C₆₀, C₇₀) hollow spheres were fabricated by controlled oxidation of fullerene monoanions under solvothermal conditions. Scanning electron microscope and transmission electron microscope showed the uniform size and the hollow nature of the spheres. Matrix-assisted laser desorption ionization time-of-flight mass spectrum and Raman spectroscopy proved that the hollow spheres are mainly composed of pristine fullerene. An Ostwald ripening mechanism is proposed.     

Stepwise shock compression of C70 fullerene

Shock-induced phase transitions of C₇₀ fullerene are experimentally studied up to a pressure of 36 GPa and a temperature of 1200 K. Pressure–temperature histories of C₇₀ specimens are estimated and overlaid on the tentative phase diagram of C₇₀. The crystalline phase of fullerene C₇₀ with a hexagonal close-packed structure remained practically unchanged under stepwise shock compression up to а pressure of 8 GPa. Contrariwise the crystalline phase of fullerene C₇₀ with a rhombohedral structure fully converted to the phase with a cubic structure under similar conditions. Shock-induced transformation of the hexagonal phase into the face-centered cubic phase was observed at pressures in the range of 9–19 GPa. The amount of transformed material increases with the shock intensity. Upon further increase in the shock pressure, the destruction of C₇₀ molecules begins. In the sample recovered from 26 GPa, we observed the traces of C₇₀ with a face centered cubic structure only. The destruction of C₇₀ is accompanied by formation of graphitic carbon.     

Increase of photoluminescence from fullerene‐doped polymers under laser irradiation

Photoluminescence (PL) from fullerene (C₆₀ and C₇₀)‐doped polymers such as poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(methyl phenyl silane) (PMPS) and poly(phenyl silsesquioxane) (PPSQ) increases gradually under laser irradiation in air (but not in vacuum and in nitrogen) and eventually becomes visible to the naked eye. Concomitantly, the PL peak is broadened and, in most cases, blue‐shifted. No such PL increases are observed for pure C₆₀ films made by vacuum vapor deposition and pure polymer films. Among the polymers used, fullerene‐doped PMMA has the greatest PL increase after several hours of laser irradiation and fullerene‐doped PMPS has the highest rate of PL increase at the initial stage of the laser irradiation. To gain an insight into the mechanism of the PL increase, laser‐irradiated fullerene‐doped PMMA samples were analyzed by UV‐Vis spectrophotometer, FT‐IR, mass spectrometry, GPC and NMR. The results show that the PL increase can be attributed to CH₆₀O_n‐polymer (or C₇₀O_n‐polymer) and oxidized fullerene‐polymer adducts formed by some laser‐induced photochemical reactions among fullerenes, oxygen and polymers.     

Separation of fullerenes C60 and C70 using a crystallization‐based process

A crystallization‐based process that separates pure fullerenes C₆₀ and C₇₀ from their mixture using o‐xylene as the solvent has been developed. Isothermal solid–liquid equilibrium phase diagrams of the C₆₀‐C₇₀‐o‐xylene ternary system for a number of temperatures were first determined at 1 atm. Taking advantage of the shift in solvent‐free composition of the C₆₀‐C₇₀ double saturation point with temperature and based on the solid solution‐forming phase behavior between C₆₀ and C₇₀, the flowsheet of a general crystallization process was then synthesized. It involved the fractionation of a C₆₀‐C₇₀ fullerene mixture into C₆₀‐rich and C₇₀‐rich solid solutions using temperature‐swing crystallization, followed by purification of the solid solutions with multistage crystallization into pure C₆₀ and C₇₀ solids. To demonstrate process feasibility, bench‐scale batch experiments were performed using a commercially available fullerene mixture that was pretreated by adsorption to remove higher fullerenes. C₆₀ and C₇₀ solids of purity higher than 99 wt % were obtained. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Convenient syntheses of fullerynes for ‘clicking’ into fullerene polymers

Alkyne-functionalized fullerenes (fullerynes) were designed and conveniently synthesized via Bingel reaction in one step with high yields. They were used to react with azido-functionalized polystyrene (PS) via Huisgen [3 + 2] cycloaddition ‘click’ chemistry to form two fullerene polymers: one with C₆₀ tethered to the end of a PS chain (C₆₀-1PS) and the other with C₆₀ tethered at the junction point of two PS chains of identical molecular weight (C₆₀-2PS). The fullerene polymers were characterized by ¹H NMR, ¹³C NMR, FT-IR, MALDI-TOF mass spectrometry and SEC. The results showed that the fullerene polymers are well-defined with narrow polydispersity and high fullerene functionality. Besides, aggregation of C₆₀ in THF was observed in the SEC traces. The optical properties of the fullerene polymers were studied by UV–Vis absorption spectroscopy, and the results suggested that the PS chain(s) on the fullerene core has no remarkable effect on the optic property of C₆₀. The thermal properties of the fullerene polymers were studied by TGA and DSC, and the results indicated that the two fullerene polymers with different C₆₀ content and distinct molecular topology may have different self-assemble architectures in the solid state. The well-defined fullerene polymers can be used as model compounds to study the self-assemble architecture of shape amphiphiles based on polymer-tethered molecular nanoparticles.     

X-ray photoelectron spectroscopy investigation on the interaction of polyvinylcarbazole and fullerene

Summary Using X-ray Photoelectron Spectroscopy (XPS) technique, the interaction mechanism between polyvinylcarbazole (PVK) and fullerene (C₆₀) in photoconductive PVK film doped with C₆₀ was studied. PVK and fullerene can form electron transfer complex according to the molar ratio of PVK unit and C₆₀ being about 2:1 in room temperature, and the formation and dissociation of the complex are reversible with the change of temperature. The formation of complex is the key to improve the photoconductivity of PVK.     

Portlandite content and ionic transport properties of hydrated C3S pastes

This paper presents the results of a C₃S paste characterization study. The objective was to determine the parameters needed to model the process of degradation. The experimental study focused on determining the portlandite content and the ionic diffusion coefficients of C₃S paste. The molar C/S ratio of C–S–H in hydrated C₃S pastes was also investigated. The portlandite content was determined with an experimental method based on an electron microprobe analysis.This method leads to a portlandite mass content of 24.4 ± 2.3%. The diffusion coefficient of each ionic species was determined by inverse analysis of diffusion test data performed on hydrated C₃S samples using a multiionic transport model.     

A highly improved method for purification of fullerenes applicable to large-scale production

Purification of fullerenes was accomplished by filtration of fullerene extract through a thin layer of activated carbon. Under the optimum conditions, chlorobenzene was used as eluent to diminish the volume of solvent remarkably. The thickness of the carbon layer was only 3-17 mm (activated carbon/fullerene mixture (w/w)=1/3-1/10) enough to obtain pure C₆₀ in good yield. The method presented here is much more convenient than column chromatography commonly used so far and can be applicable to large-scale production of pure C₆₀ and C₇₀. From a mechanistic point of view, fullerenes are considered to be discriminated in the activated carbon pores which have a little larger diameter than the size of fullerenes (1.0-2.0 nm) by π-π interaction between fullerene surface and fused aromatic rings composing the pores.     

Oxygen reduction on poly(4-vinylpyridine)-modified ordinary pyrolytic graphite electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine in acid solutions

Poly(4-vinylpyridine) (PVP) has been used to modify ordinary pyrolytic graphite (OPG) electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine (CoTsPc) in acid solutions. These modified electrodes were prepared in different manners and characterized by cyclic voltammetry. Their electrocatalytic activity for oxygen reduction and stability in 0.05M H₂SO₄ solutions was examined at room temperature. The OPG/CoTsPc/PVP modified electrodes were found to be more active for oxygen reduction in 0.05M H₂SO₄ solutions as compared to the electrode with adsorbed CoTsPc on OPG without PVP. The increase in activity is due to the formation of an adduct between PVP and CoTsPc. U.v.-visible and FTIR studies provide evidence for such adduct formation. Over a 10 h period the activity of the OPG/CoTsPc/PVP system was essentially constant while that of OPG/CoTsPc without polymer decreased by a substantial amount (about 37%). The PVP layer inhibits the diffusion of the CoTsPc and/or Co out of the complex into the solution phase. The stability of the OPG/CoTsPc/PVP system may also be due to low solubility of the adduct between PVP and CoTsPc in a 0.05M H₂SO₄ solution. Thicker films of PVP decreased the diffusion limiting oxygen reduction current. The effect of pH of the electrolyte solution on the activity of such PVP-modified electrodes for oxygen reduction has also been investigated.     

Gas diffusion and dielectric studies of polystyrene‐fullerene compositions

Polystyrene‐fullerene compositions containing up to 0.45 mol % (3 wt %) fullerene C₆₀ were investigated. It was established that the addition of fullerene to polystyrene (PS) leads to an increase of molecular packing density and so influences the transport of small molecules through the polymer films. Gas diffusion through films of PS‐fullerene compositions is slower than through PS films, and gas separating properties of compositions are higher. Dielectric studies showed that the fullerene is distributed as clusters in the polymer matrix of solid composition prepared from a toluene solution of PS and fullerene. Heating without air to the temperature higher than PS glass transition leads to increasing relaxation time of α‐transition in PS of compositions containing >0.15 mol % (1 wt %) fullerene. This effect is caused by rather strong interaction of PS chains via fullerene molecules entered into the PS‐fullerene complex. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2946–2951, 2002     

Electrochemical quartz crystal microbalance studies of thin-solid films of higher fullerenes: C76, C78 and C84

Thin-solid films of higher fullerenes, viz. C₇₆, C₇₈ and C₈₄, were prepared by the drop coating technique and characterized by simultaneous cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. Properties of the films were compared with those reported earlier for the C₆₀ and C₇₀ thin-solid films. The effect of nature of the counter cation on electrochemical properties of the films has been probed by employing acetonitrile solutions of two different 0.1 M supporting electrolytes, namely tetra(n-butyl)ammonium (TBA⁺) hexafluorophosphate and potassium hexafluorophosphate. Stability of the films with respect to dissolution depends on the fullerene oxidation state as well as on the nature of both the fullerene in the film and the counter cation in the supporting electrolyte. The TBA⁺ counter cation ingress to the film for compensation of the negative charge of the reduced fullerene is accompanied by the acetonitrile solvent intake. The number of acetonitrile molecules per TBA⁺ counter cation entering the film is higher the higher the fullerene. Also, the Langmuir films of higher fullerenes were prepared at the air-water interface and the film morphology was characterized by the Brewster angle microscopy.     

Rheological examination of C60 in low density solutions

Fullerene (C₆₀) in solutions of decahydronaphthalene (decalin) and a petroleum solvent viscous standard (PSVS) were studied to understand the rheological properties of fullerene-laden solutions. Although fullerene solubility limits have been published for a variety of solvents, little has been reported on the effect that fullerenes have on flow properties of fluids. In this study, the solvents were studied up to the point of saturation, whereby measurements of solubility, density, viscosity and elasticity were conducted varying the concentration level of C₆₀. Rheological measurements based on molecular interactions and on distortion of the flow were studied. No significant elastic contribution from the fullerenes resulted for the solutions below saturation. A pseudoplastic behavior with a lubrication effect imparted by the C₆₀ molecules was observed in the decalin solutions at concentrations below the saturation level. The PSVS solutions remain Newtonian for all C₆₀ concentrations while leading to an increase in viscosity.     

Synthesis and characterization of gold‐based mesoscopic additives for polymers

A method for the controlled synthesis of alkanethiol‐derivatized gold clusters to be used as fillers for polymeric nanocomposites has been developed. Gold clusters embedded in poly(N‐vinyl pyrrolidone) (PVP) were obtained by reduction of AuCl₄^? with ethylene glycol in the presence of PVP as a stabilizer. The gold/PVP system was separated from the reactive mixture by flocculation with acetone, and this material was treated with a dodecanethiol/ethanol solution to produce thiol‐derivatized gold clusters. Then, the clusters were dispersed in polystyrene/chloroform solutions and highly transparent purple‐colored nanocomposite films were obtained by solution casting. This preparative scheme allows one to obtain high‐purity nanocomposites, with complete control over the filler percentage and size. Copyright © 2004 Society of Chemical Industry     

Hydrogen in fullerites

The peculiar kind of fullerene molecule structure is also reflected in the crystal structure of fullerites. The cubic lattices of metal fullerides and hydrofullerenes behave similarly to the cubic lattices of different metals and alloys. They form interstitial solid solutions when impurity elements are distributed in octahedral and tetrahedral interstitial sites. By replacement of C₆₀ and C₇₀ molecules in lattice sites they make up substitution solid solutions. Forming exo- and endohedral compounds, the fullerene molecules, located in sites of the crystal lattice, can modify greatly the crystal properties with no change of crystalline structure. Some peculiarities of fullerite crystalline structures will be discussed in the present paper.     

Synthesis of (C5H5)2Zr(O2C)CH3 and (C5H5)2Zr(O2C)CH2CH3 for olefin polymerization

Summary (C₅H₅)₂Zr(O₂C)CH₃ and (C₅H₅)₂Zr(O₂C)CH₂CH₃ complexes were synthesized, characterized and activated with MAO for ethylene polymerization. The highest catalytic activity was achieved at Al/Zr molar ratio of 3000 for both systems. The effects of the size of the R group in the carboxylate ligands, the Al/Zr molar ratio and reaction temperature on the catalytic activity and polymer properties were studied and discussed.     

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

We dissolve C₆₀, C₇₀ or C₈₄ molecules in benzene and change the fluid state from a gas–liquid two-phase region (25.0 °C) to the critical point (289.0 °C) and from the critical point to the original state (25.0 °C) along the gas–liquid coexistence curve. We find that particle-like and whisker-like nano/micro clusters, which are composed of C₆₀ molecules, deposit on the surface of a silicon substrate placed vertically in C₆₀/benzene solution during the temperature change, whereas no appreciable clusters are detected on the silicon substrate in either C₇₀/benzene or C₈₄/benzene solutions. The clusters, in which fcc lattice structures are formed by C₆₀ molecules, remain stable in the solution. The present result suggests that C₆₀ molecules can be separated and extracted from a mixture of C₆₀, C₇₀ and C₈₄ molecules dissolved in benzene.