Presence Of C60 Research Articles

Methyl methacrylate polymerization in the presence of C60 (C70) and molecular characteristics of fullerene-containing poly(methyl methacrylate)

Kinetics was studied of bulk polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate in the presence of tri-n-butylborane and fullerene C60 (or C70) at variable ratio initiator: fullerene. The deceleration of the polymerization in the first stage of the reaction (below 10% conversion) was established by dilatometric method that depended on the fullerene concentration and the mode of its addition to the monomer. It was shown that at similar ratios initiator: fullerene the C60 inhibited the polymerization process considerably stronger than C70. The gel-permeation chromatography revealed the widening of the molecular weight distribution of the poly(methyl methacrylates) containing C60 or C70 compared to its analog synthesized under the same conditions without fullerene. It was established that in the fullerene-containing poly(methyl methacrylates) all the framework nanospecies are linked by covalent bonds and are mostly accumulated in the low-molecular fractions. The effect of the covalently bound fullerene on the molecular characteristics of polymers were investigated by translational isothermal diffusion, high-speed sedimentation, and viscometry

The Synthesis and Characterization of Poly Vinyl Chloride Chemically Modified with C60

The fullerenated poly vinyl chloride was synthesized by the addition reaction of azido‐substituted poly vinyl chloride with C60. Structural characterization carried out using Raman and FTIR spectroscopy confirm the presence of C60 chemically bound in the new compound. Also, the photoluminescence properties of fullerenated poly vinyl chloride are considerably changed from those of C60

C60 reduces the flammability of polypropylene nanocomposites by in situ forming a gelled-ballnetwork

The thermal and flame retardancy properties of polypropylene/fullerene(PP/C60) nanocomposites were investigated by thermogravimetric analysis (TGA),differential scanning calorimetry (DSC) and cone calorimetry with theC60 loading varied from 0.5 to 2% by weight. Dispersion ofC60 in the PP matrix was characterized by transmission electron microscopy (TEM) andoptical microscopy (OM). TGA and DSC results showed that the presence ofC60 could remarkably enhance the thermal property and cone calorimeter measurements suggested thatC60 could to some extent reduce the flammability of PP, with a significant reduction in peak heatrelease rate and a much longer time to ignition. Furthermore, the larger the loading level ofC60, the better the flame retardancy property ofPP/C60 nanocomposites. The flame retardation mechanism and corresponding model wereproposed with the help of rheological measurements, TEM and x-ray diffraction.C60 reduced the flammability of PP by trapping free radicals in the gas phase and in situforming a gelled-ball crosslink network to improve the flame retardancy of PP in thecondensed phase. Finally, this suggested mechanism was supported by the results ofadvanced rheological extended systems (ARES), gel content, infrared spectrum, OM, andatomic force microscopy (AFM) measurements.

Pristine (C60) and Hydroxylated [C60(OH)24] Fullerene Phototoxicity towards HaCaT Keratinocytes: Type I vs Type II Mechanisms

The increasing use of fullerene nanomaterials has prompted widespread concern over their biological effects. Herein, we have studied the phototoxicity of gamma-cyclodextrin bicapped pristine C 60 [(gamma-CyD) 2/C 60] and its water-soluble derivative C 60(OH) 24 toward human keratinocytes. Our results demonstrated that irradiation of (gamma-CyD) 2/C 60 or C 60(OH) 24 in D 2O generated singlet oxygen with quantum yields of 0.76 and 0.08, respectively. Irradiation (>400 nm) of C 60(OH) 24 generated superoxide as detected by the EPR spin trapping technique; superoxide generation was enhanced by addition of the electron donor nicotinamide adenine dinucleotide (reduced) (NADH). During the irradiation of (gamma-CyD) 2/C 60, superoxide was generated only in the presence of NADH. Cell viability measurements demonstrated that (gamma-CyD) 2/C 60 was about 60 times more phototoxic to human keratinocytes than C 60(OH) 24. UVA irradiation of human keratinocytes in the presence of (gamma-CyD) 2/C 60 resulted in a significant rise in intracellular protein-derived peroxides, suggesting a type II mechanism for phototoxicity. UVA irradiation of human keratinocytes in the presence of C 60(OH) 24 produced diffuse intracellular fluorescence when the hydrogen peroxide probe Peroxyfluor-1 was present, suggesting a type I mechanism. Our results clearly show that the phototoxicity induced by (gamma-CyD) 2/C 60 is mainly mediated by singlet oxygen with a minor contribution from superoxide, while C 60(OH) 24 phototoxicity is mainly due to superoxide.

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene–polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C60 and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C60–SIS/SBS were found to decrease with increasing C60 concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C60. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C60 sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C60 concentration and exposure time, and in irradiated systems containing as little as 0.2wt% C60, a significant decrease in adhesion was observed. Estimated Tg (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30–40°C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.

Synthesis of gold nano-wire and nano-dumbbell shaped colloids and AuC60 nano-clusters

A technique for the fabrication of colloidal gold nano-wire and nano-dumbbell shaped particles using rod shaped viruses as templates is described. The gold (Au) encapsulation process was accomplished by the precipitation of gold chloride from aqueous solutions. When this process was conducted in the presence of C60, small nano-cluster composites of AuC60 formed.

Effect of carbon nanomaterials on calcium carbonate crystallization

The addition of the water-soluble carbon nanomaterials, fullerenol (C60(OH)n), hydroxylated single walled carbon nanotubes (HO-SWNTs) and isophthalic acid functionalized-SWNTs (IPA-SWNTs), alter the morphology and crystal phase of CaCO3 precipitates form aqueous solution. CaCO3 precipitation in the presence of C60(OH)n results in the formation of spherical features, 5-pointed flower shaped clusters, and triangular crystals as opposed to the usual rhombic crystals. In addition, the meta-stable vaterite phase is observed with the addition of C60(OH)n. The effect on crystal growth of the C60(OH)n is not a simple function of the pH of the solution, although it may be due to reactivity of the hydroxyl groups. Precipitation with water-soluble HO-SWNT and IPA-SWNTs produces CaCO3 coated SWNTs with the CaCO3 being amorphous rather than crystalline.

Dendrimer Effects on Intermolecular Energy-Transfer of Photoexcited Triplet States of Dendritic Multiporphyrin Arrays and Electron Transfer vs Fullerene[60

Abstract Photochemical and photophysical properties of the triplet excited states of dendritic multiporphyrins arrays (nPZn, n = 1, 3, and 7) have been investigated by measuring the nanosecond transient absorption spectra in the visible and near-IR regions with changing the generation number. Intermolecular triplet–triplet annihilation rates decrease with the dendrimer generation, which was interpreted on a proposed kinetic model assuming that the excited triplet energy almost localizes in one PZn unit in nPZn. In the presence of C60, intermolecular electron-transfer takes place via the excited triplet states of nPZn (3nPZn*), yielding the cation radical of nPZn (nPZn•+) and the anion radical of C60 (C60•−) in PhCN. Deceleration of the electron-transfer rate-constants from 1PZn to 3PZn and the acceleration from 3PZn to 7PZn were observed, in which the latter tendency was interpreted by considering an increase in effective encounter radius for 37PZn*. The observed small change of the rate constants for back electron transfer between the oppositely charged species with the dendrimer generation was also reasonably interpreted by taking a smaller effective radius due to electrostatic attraction into consideration. Dendrimer generation effect was also observed for the intermolecular hole-transfer process.

C 60 bonding to graphite and boron nitride surfaces

The present study focuses on the interaction of C60 with the surfaces of highly oriented pyrolitic graphite (HOPG) and sp2-bonded boron nitride (BN). The nanocrystalline BN film was deposited by mass selected ion beams and features an sp2-bonded surface layer, which covers a cubic phase BN film. The first part of the experiment is the sequential deposition of C60, which is monitored by photoelectron spectroscopy in the x-ray (XPS) and ultraviolet (UPS) regime. The growth of the C60 layer on HOPG is close to a layer-by-layer growth mode, but on the BN surface island growth is favored. No charge transfer or chemical reaction (e.g., carbide formation) between the fullerene layer, and the underlying substrate is observed in either case. In the second part of the experiment the samples are heated at a rate of 10 K/min while simultaneously recording the UPS VB spectra. The complete desorption of C60 from the HOPG surface occurs in a small temperature interval between 510–530 K. For the sp2 BN surface the majority of C60 desorbs around 493 K, about half a monolayer (ML) remains, and the C60 concentration decreases gradually with increasing temperature; less than a tenth of a ML can be detected even at 1000 K. The first desorption event at 493 K is attributable to the multilayer desorption from islands. The remaining C60 directly in contact with the BN surface is then removed in a large temperature interval between 500 and 1000 K which indicates the presence of a multitude of adsorption sites. The presence of C60 on the BN film surface also induces a band bending and related B 1s and N 1s core level shifts. An upward band bending is present in the C60 overlayer, which indicates that defects are responsible for the pinning of the Fermi level at the interface.

Interaction of C60 with Isoelectronic Surfaces: Graphite and Hexagonal Boron Nitride

ABSTRACTIn the present study we focus on the interaction of C60 with sp2 boron nitride (BN), a surface that is isoelectronic to graphite. The nanocrystalline BN substrate was deposited by mass selected ion beam and consists of an sp2 surface layer, which covers a cubic-BN film. The interaction and electronic properties of the C60-BN system are observed by photoelectron spectroscopy in the x-ray (XPS) and ultraviolet regime (UPS). The experiment is initiated by sequential deposition of C60 and the overlayer growth proceeds via island formation. In a second step the sample is annealed at a rate of 5–10 K/minute while simultaneously recording the UPS spectra. The majority of C60 desorbs from the sp2 BN surface at 493 K. The remaining C60 (initially about 0.6 ML) is gradually removed with increasing temperature (up to 813 K) but never completely desorbed and presumably attached at surface imperfections or grain boundaries of the nanocrystalline material. No carbide formation, preferential interaction of C60 with either element or a charge transfer are observed. The presence of C60 induces an upward band bending and related peak shifts in the sp2 BN surface layer and to a lesser extent in the underlying c-BN bulk. An upward band bending is likewise observed in the C60 overlayer, and the Fermi level has therefore to be pinned by defects in the interface region. The layered structure of the BN film allows to probe the extension of the space charge layer in the BN film.

A dynamic continuum of nanostructured carbons in the combustion furnace

The presence of C60, carbon onions and higher fullerenes are confirmed in products from a carbon black combustion furnace. Acetylenic, C2, units participate in the formation and growth phases in the combustion flame. High-resolution TEM data clearly show fullerenes incorporated into the matrix of the carbon; MALDI mass spectral data show C60 and higher fullerenes in the soot itself. The toluene extracts of experimental carbons also contain C60.

Study of Molecular Complex Formation between [60]Fullerene and Two Series of Donors by the NMR Method

Formation of molecular complexes between [60]fullerene and (i) a series of aromatic hydrocarbons, namely, anthracene, acenaphthene, phenanthrene, pyrene, durene, pentamethylbenzene, and hexamethylbenzene, and (ii) a series of pyridines, namely, pyridine, 2-picoline, 3-picoline, 4-picoline, 2,6-lutidine, and 2,4,6-collidine has been studied in CCl4 medium by NMR method. [60]Fullerene has been shown to form 1:1 molecular adducts with the above series of compounds. Formation constants (K) of the above complexes have been determined from the systematic variation of NMR chemical shifts of specific protons of the donors in the presence of C60. The K values of [60]fullerene complexes with pyridine, 3-picoline, and 4-picoline yield good estimates of the Hammett constant, ρ, for the complexation reaction.

60]Fullerene and three [60]fullerene derivatives in membrane model environments

Aggregation of C60 and of three C60 derivatives in phosphatidylcholine liposome model membranes was studied via photophysical investigations. The triplet properties of these fullerenes, including the absorption spectrum between 400 and 900 nm, molar absorption coefficient, quantum yield of formation and/or quantum yield for the photosensitised production of 1O2 were determined in benzene solution and in liposomes. One of the derivatives was a cyclopropyl-fused hexa-addended C60 containing as addend C(CO2C18H37)2 (1). The other two derivatives were cyclohexyl-fused C60 with leucine (2) or hydrophilic acidic (3) mono-addend functionalisation. The synthesis of derivative 2, by thermal extrusion of sulfur dioxide from the corresponding sulfone in the presence of C60, is described. [60]Fullerene and derivative 1 show no T–T absorption in liposomes, although they do so in benzene solution (with a low triplet quantum yield for hexa-addended 1). The absence of triplet–triplet absorption in liposomes is indicative of fullerene aggregation. By contrast, the amphiphilic mono-addend derivatives 2 and 3 present appreciable T–T absorption in liposomes, although less marked than in benzene solution. Mono-addend functionalisation therefore appears to be an interesting way to prevent or diminish fullerene aggregation. Moreover, in this type of derivatisation most of the photophysical properties of pristine [60]fullerene are retained.

Formation of a protective film on a copper friction surface in the presence of fullerene C60

The influence of C60 additive in industrial oil on the structure of the friction surface of copper foil in a steel-copper sliding friction pair is investigated by wide-angle x-ray diffraction, scanning electron microscopy, and hardness testing. The presence of C60 in the lubricant leads to the formation of a thin film (of thickness <1000 A) on the friction surface of the copper, where it protects the surface layers of the latter against major structural changes and helps to improve the tribological characteristics.

Radical polymerization of styrene in the presence of C60

Radical polymerizations of styrene in the presence of C60 have been conducted at 90°C in benzene using benzoyl peroxide (BPO) as initiator. The behaviors of C60 are investigated by monitoring BPO concentration, C60 content, and polymerization time. It is found that C60 acts like a radical absorber which multiply absorbs primary radicals from BPO and propagating radicals. Therefore, in the presence of C the yield and molecular weight decrease significantly. However, the molecular weight distribution is narrowed down by its coupling characteristics. At the beginning of the reaction, owing to the radical-absorbing effect of C60, it makes the chain-propagation restricted. However, the number of polystyrene chains added to C60 increases with polymerization time. Direct dilatometric experiment proves that C60 is mainly as inhibitor for radical polymerization of styrene by benzoyl peroxide. Besides, the glass transition temperature (Tg) of the copolymers increases with increasing content of C60. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2969–2975, 1999

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C60) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (Rp) and the molecular weight of resulting poly(MMA) decreased with increasing C60 concentration ((0–2.11) × 10−4 mol/L). The molecular weight of polymer tended to increase with time at higher C60 concentrations. Rp at 50°C in the presence of C60 (7.0 × 10−5 mol/L) was expressed by Rp = k[MAIB]0.5[MMA]1.25. The overall activation energy of polymerization at 7.0 × 10−5 mol/L of C60 concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r1 = 0.53, r2 = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C60 (7.15 × 10−5 mol/L) were similar to those (r1 = 0.46, r2 = 0.52) in the absence of C60. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998

Polyelectrolyte-Containing Fullerene I: Synthesis and Characterization of the Copolymers of 4-Vinylbenzoic Acid with C60

Polymerization of 4-vinylbenzoic acid in the presence of C60 using free radical initiator resulted in covalent incorporation of C60 in the polymer structure. Incorporation of the C60 moieties in the polymer was established by IR, NMR, and UV−vis spectroscopy. The solution UV−vis spectra of these C60-containing copolymers appear to be dominated by scattering, obscuring specific electronic excitation features associated with the fullerene. UV−vis spectral analysis of filtrate fractions collected using filters of varying pore sizes indicates that polymers form microgels with polydisperse particle sizes (micron to submicron dimensions) in solution that extensively scatter at shorter wavelengths. Differences in the fluorescence properties of the filtered fractions and unfiltered samples were observed. Furthermore, fluorescence emission spectra of a copolymer showed wavelength-dependent behavior. Polyelectrolyte behavior of these copolymers was studied by concentration dependent viscosity changes of the polymer...

Anomalies in the microwave conductivity of a polycrystalline C60 membrane

A study is reported of an anomaly in the microwave conductivity of a polycrystalline C60 membrane at Tc=260 K (the transition width is 30 K). Raman scattering measurements indicate that the sample is the C60 fullerite without any signs of graphitization, amorphous phase, or the presence of C70, and that the detected microwave conductivity jump can be unambiguously identified as due to the C60 phase.

Photochemical Reaction of Furans in the Presence of [60] Fullerene

The first evidence was presented which supports a photochemical pathway during the reaction of furan derivatives in the presence of C60, which was formerly believed to proceed via a thermal [2+4]-concerted cycloaddition reaction of furans with C60. LD-TOF-MS, UV-vis, FT-IR and 1H-, 13C-NMR spectra showed that

Synthetic and Computational Studies on Symmetry-Defined Double Cycloaddition of a New Tris-Annulating Reagent to C60

For the purpose of doubly functionalizing fullerenes, new tris-annulating reagents 2(n) have been developed. The reagents carry, in one molecule, two cyclopropenone acetals which are connected with an n-carbon methylene tether. Upon thermolysis of 2(n) in the presence of C60, the reagent undergoes [3 + 2] cycloaddition reaction twice in a regio- and stereoselective manner to give Cs and C2 organofullerenes bearing two cyclopentenone acetals. The selectivity varies as the function of the tether structure. The experiments have shown that, in each series of different tether lengths, one can obtain one or two diastereomeric double adducts out of several structural possibilities. The selectivity of the reaction did not conform to the prediction made on the basis of previous knowledge on intermolecular double additions but was found to be correlated to the conformational strain of the tether moiety, which can be estimated by a newly developed “double differential protocol”. Systematic studies on the reliability...