Thermodynamic properties of C<Subscript>60</Subscript> polyfullerites

This paper discusses the results of calorimetric studies of the 1D C₆₀ (orthorhombic) and 2D C₆₀ (tetragonal and rhombohedral) fullerites, as well as of the graphite-like polyfullerite, which are produced from a starting C₆₀ fullerite subjected to a pressure of 1–8 GPa at temperatures ranging from 300 to 1270 K. The analysis is made primarily of the C _p ⁰ heat capacity measurements performed in adiabatic calorimeters in the 5-to 350-K range.     

Polyaniline composites with fullerene C<Subscript>60</Subscript>

Polyaniline-fullerene composites were prepared by the introduction of fullerene during polymerization of aniline. An investigation of the composites using FTIR and ¹³C NMR spectroscopy indicated interaction between fullerene and the imine groups of polyaniline. The formation of a polyaniline-fullerene complex with a structure corresponding to a doped polyaniline was proved by wide-angle x-ray scattering analysis. The conductivity of composites is more than four orders of magnitude higher than that of undoped polyaniline and that of fullerene. Improvement in the thermal stability of composites was evaluated using TGA.     

C<Subscript>60</Subscript> fullerene decoration of carbon nanotubes

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C₆₀ molecule to a defect on the nanotube surface.     

Stone-Wales transformation paths in fullerene C<Subscript>60</Subscript>

The mechanisms of formation of a metastable defect isomer of fullerene C₆₀ due to the Stone-Wales transformation are theoretically studied. It is demonstrated that the paths of the “dynamic” Stone-Wales transformation at a high (sufficient for overcoming potential barriers) temperature can differ from the two “adiabatic” transformation paths discussed in the literature. This behavior is due to the presence of a great near-flat segment of the potential-energy surface in the neighborhood of metastable states. Moreover, the sequence of rupture and formation of interatomic bonds is other than that in the case of the adiabatic transformation.     

X-ray diffraction analysis of C<Subscript>60</Subscript> fullerene powder and fullerene soot

C₆₀ fullerene powder and fullerene soot are examined by the method of small-angle X-ray diffraction. Small-angle diffraction patterns constructed in the Guinier coordinates make it possible to find the radii of inertia of scattering elements. The small-angle diffraction scattering findings agree well with large-angle X-ray diffraction data.     

Molecular properties of C<Subscript>60</Subscript> fullerene complexes with cycle-containing polymers in solutions

The donor-acceptor complexes of the C₆₀ fullerene with cycle-containing polymers, namely, poly(2,6-dimethyl-1,4-phenylene oxide) (PPhO) and poly(N-vinylpyrrolidone) (PVP), are studied. A comparative analysis of the hydrodynamic and electrooptical properties of the initial polymers and their complexes with C₆₀ in solutions demonstrates that the C₆₀ fullerene has a restructuring effect on the polymer macromolecule, thus decreasing the degree of asymmetry of the macromolecular structure.     

Effect of C<Subscript>60</Subscript> fullerene additions on the mechanical properties of a polybutadiene-styrene raw rubber

The effect of small C₆₀ fullerene additions on the mechanical properties (upon uniaxial tension) and structure of a polybutadiene-styrene raw rubber is studied.     

Translocation mechanism of C<Subscript>60</Subscript> and C<Subscript>60</Subscript> derivations across a cell membrane

Carbon-based nanoparticles (NPs) such as fullerenes and nanotubes have been extensively studied for drug delivery in recent years. The permeation process of fullerene and its derivative molecules through membrane is essential to the utilization of fullerene-based drug delivery system, but the mechanism and the dynamics of permeation through cell membrane are still unclear. In this study, coarse-grained molecular dynamics simulations were performed to investigate the permeation process of functionalized fullerene molecules (ca. 0.72 nm) through the membrane. Our results show that single functionalized fullerene molecule in such nanoscale could permeate the lipid membrane in micro-second time scale. Pristine C₆₀ molecules prefer to aggregate into several small clusters while C₆₀OH₁₅ molecules could aggregate into one big cluster to permeate through the lipid membrane. After permeation of C₆₀ or its derivatives into membrane, all C₆₀ and C₆₀OH₁₅ molecules disaggregated and monodispersed in the lipid membrane.

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The effect of water on the stability of C<Subscript>60</Subscript> fullerene nanowhiskers

The morphology of C₆₀ precipitates synthesized by using isopropyl alcohol (IPA) added with water was investigated in order to know the effect of water on the growth of C₆₀ nanowhiskers (C₆₀NWs) in C₆₀–toluene–IPA solution systems. The stability of C₆₀NWs decreased and granular crystals of C₆₀ were formed in the solutions when IPA added with an excess amount of water was used in the liquid–liquid interfacial precipitation method. The C₆₀NWs were found to be destabilized with time in the solutions added with water. The C₆₀NWs dried in air showed similar Raman profiles irrespective of the use of IPA with and without water addition. The Raman profiles of granular C₆₀ single crystals showed the base lines much flatter than those of C₆₀NWs, indicating that C₆₀NWs possess a disordered crystal structure. By optimizing the growth condition, short C₆₀NWs with aspect ratios ranging from 3 to 10 and an average length of about 1.8 μm were successfully fabricated. The short C₆₀NWs are expected to be applicable for electrodes of organic thick film solar cells.     

Thermal desorption states of C<Subscript>60</Subscript> fullerene molecules in polymer matrices

Polymer-C₆₀ fullerene composite coatings are studied using thermal desorption mass spectrometry. It is found that thermal desorption spectra of C₆₀ fullerene molecules can exhibit several resolved peaks (at a specified heating rate) corresponding to thermal desorption states. The relative intensity of the thermal desorption peaks depends on the procedure used for preparing the composite coatings, in particular, on the time of sedimentation of the polymer-fullerene suspension. The occurrence of different stages in thermally stimulated desorption of C₆₀ fullerene molecules is explained by the fact that the fullerene molecules can exist in several phase states characterized by different densities and degrees of ordering in the polymer matrix.     

Stability of C<Subscript>20</Subscript> fullerene chains

The stability of (C₂₀)_N metastable chains, where C₂₀ fullerenes are joined by tight covalent bonds, is analyzed by numerical simulation using a tight-binding potential. Various channels of losing the chain-cluster structure of the (C₂₀)_N complexes have been determined including the decay of the C₂₀ clusters, their coalescence, and the separation of one C₂₀ fullerene from a chain. The lifetimes of the (C₂₀)_N chains with N = 3–7 for T = 2000–3500 K are directly calculated by the molecular dynamics method. It has been shown that, although the stability of the chains decreases with an increase in N, it remains sufficiently high even for N ? 1. An interesting lateral result is the observation of new (C₂₀)_N isomers with the combination of various intercluster bonds with the maximum binding energy of fullerenes in the chain.     

Stepwise computational synthesis of fullerene C<Subscript>60</Subscript> derivatives. Fluorinated fullerenes C<Subscript>60</Subscript>F<Subscript>2<Emphasis Type="Italic">k</Emphasis></Subscript>

Reactions of fullerene C₆₀ with atomic fluorine are studied by the unrestricted broken spin symmetry Hartree-Fock (UBS HF) approach implemented in semiempirical codes based on the AMI technique. The calculations are focused on a successive addition of a fluorine atom to the fullerene cage following the indication of the highest chemical susceptibility of the cage atom, which is calculated at each step. The proposed computational synthesis is based on the effectively unpaired-electron concept of the chemical susceptibility of fullerene atoms. The obtained results are analyzed from the standpoints of energy, symmetry, and the composition abundance. A good fitting of the data to experimental findings proves a creative role of the suggested synthetic methodology.     

Photostability of a C<Subscript>60</Subscript> fullerene coating as a solid-phase photosensitizer of singlet oxygen

The stability of the optical properties and the generation efficiency of singlet oxygen of a solidphase photosensitizer based on fullerene in an aqueous suspension subjected to prolonged intense irradiation with visible light are studied in comparison with a photosensitizer based on methylene blue in an aqueous solution. Changes in the absorption spectra show that, as a result of 20-min irradiation, the content of fullerene decreases by 2% from its initial value, while that of methylene blue decreases by 19%. In both cases, the dynamics of the decrease in the photosensitizing ability of the photosensitizers in the course of their irradiation correlates with the changes in their spectra, but the magnitude of this decrease in the case of the solid-phase photosensitizer is greater than the magnitude of its spectral changes because of the surface nature of the photosensitization process. The study of the absorption spectra of fullerene coatings shows that their irradiation in water or in air causes the same photodegradation of fullerene. At the same time, studies with the help of the electron spin resonance (ESR) technique reveal differences in the nature of processes undergone by fullerene in water and in air.     

X-ray emission and X-ray photoelectron spectroscopic studies of fullerene fluoride C<Subscript>60</Subscript>F<Subscript>24</Subscript>

The structure of the fullerence fluoride C₆₀F₂₄ of the T _h symmetry contains two types of chemically different carbon atoms, namely, atoms of isolated double bonds and atoms of CF groups. X-ray photoelectron and x-ray emission spectroscopic studies of C₆₀F₂₄ revealed a difference in the widths of the x-ray bands corresponding to these types of atoms. Nonempirical quantum-chemical calculations performed for C₅₉NF ₂₄ ⁺ ions with a hole in the C 1s core level of the fullerence fluoride showed that the difference in the bandwidths may be due to the fact that the vibrational states of the system are different when 1s electrons are removed from chemically nonequivalent atoms.     

Dielectric properties of liquid-crystal azomethine polymer with a side alkyl-substituted chain,doped with fullerene C<Subscript>60</Subscript>

We studied the actual and imaginary components of the dielectric constant of liquid-crystal azomethine polymer with a side chain, doped with 0.5 wt % of fullerene C₆₀, over a wide range of temperatures and frequencies; measurements were made by means of dielectric spectroscopy. By analyzing the frequency dependence of the dielectric constant, we detected the relaxation processes (α, β₁, and β₂) in the nanocomposite, corresponding to certain modes of molecular motion and described them by the Arrhenius equations (β₁- and β₂-processes) and the Vogel–Fulcher–Tamman equation (α-process). An antiplasticization effect is discovered after doping the polymer with fullerene C₆₀, which manifests itself in increasing the glass transition temperature of the nanocomposite compared to this parameter typical of pure polymer.     

C<Subscript>60</Subscript> heat capacity anomaly at the orientational phase transition

An orientational phase transition in C60 crystals was studied by differential scanning calorimetry with the highest resolution provided by this method. The temperature dependence of the specific heat ΔC _p (T) was found to have a double peak in the range 250–270 K. An analysis of the temperature dependences of heat capacity in the region of the peaks revealed that the lower temperature peak follows a power law of the type ΔC _p = A/(T?T₀)^1/2 characteristic of order-disorder second-order phase transitions, while the high-temperature peak can be identified with a diffuse Λ-shaped first-order phase transition.     

Polymerization of solid C<Subscript>60</Subscript> under C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> cluster ion bombardment

The structure transformation occurring in fullerene film under bombardment by 50 keV C₆₀⁺ cluster ions is reported. The Raman spectra of the irradiated C₆₀ films reveal a new peak rising at 1458 cm⁻¹ with an increase in the ion fluence. This feature of the Raman spectra suggests linear polymerization of solid C₆₀ induced by the cluster ion impacts. The aligned C₆₀ polymeric chains composing about 5–10 fullerene molecules have been distinguished on the film surface after the high-fluence irradiation using atomic force microscopy (AFM). The surface profiling analysis of the irradiated films has revealed pronounced sputtering during the treatment. The obtained results indicate that the C₆₀ polymerization occurs in a deep layer situated more than 40 nm below the film surface. The deep location of the C₆₀ polymeric phase indirectly confirms the dominant role of shock waves in the detected C₆₀ phase transformation.     

Cluster <Emphasis Type="Italic">ab initio</Emphasis> calculations for the C<Subscript>60</Subscript>F<Subscript>24</Subscript>, C<Subscript>60</Subscript>Cl<Subscript>24</Subscript>, and C<Subscript>60</Subscript>Br<Subscript>24</Subscript> halofullerenes

This paper reports on ab initio cluster calculations of the equilibrium geometry, electronic structure, and vibrational properties of the C₆₀, C₆₀F₂₄, C₆₀Cl₂₄, C₆₀Br₂₄ molecules.     

Equilibrium state of C<Subscript>60</Subscript>, C<Subscript>70</Subscript>, and C<Subscript>72</Subscript> nanoclusters and local defects of the molecular skeleton

The stability of C₆₀ and C₇₀ fullerenes and C₆₀ and C₇₂ nanotubes devoid of 2–12 atoms of the cluster skeleton was theoretically studied. It was established that C_n molecules with an even number of atoms remain stable, which was confirmed by experimental studies of monomolecular decay of clusters with the number of atoms n≥30. The change in the internuclear distances and in the ionization potential of nanoclusters was determined depending on the number of eliminated atoms. Such defects were shown to decrease the ionization potential of nanoclusters by 0.5–0.8 eV. The electron spectrum was calculated within the Harrison semiempirical tight-binding model in the Goodwin modification. A new parametrization of interatomic matrix elements of the Hamiltonian and atomic terms for carbon nanoclusters was suggested.