Fullerene concentration

Researchers smdied the effect of fullerene in rubber composites with different temperature range [52]. There was no substantial influence of fullerene on Tg, tan 8, and G-modulus within the temperamre range from — 150°C to —50°C (glassy state), and properties increase at mbbery state (0°C-150°C). At temperamres between — 150°C and —50°C when rubber is rigid, G-modulus is virtually independent of the fullerene concentrations between 0.065 and 0.75 phr and a single major peak in Figure 28.26 shows that the fullerene does not influence the glass transition. 

The properties are evaluated at temperamres between —50°C and 250°C (high elastic state of mbber). For mbbers in a high elastic state, an increase in fullerene concentrations is followed by a rise in modulus. It is very lucid at temperatures between — 10°C and 150°C. Most likely, it is caused... 

A comparable addition pattern with as many as five attached groups allowing further functionalization is represented in pentaaryl-fullerenes like 25-27 (Troshina et al., 2007 Zhong et al., 2006). Whereas the free acids are virtually insoluble in pure water, the use of basic water in the case of 25 (Zhong et al., 2006) and conversion of the polyacids 26 and 27 to the corresponding potassium salts leads to stable aqueous solutions with high fullerene concentrations. 

The abovementioned data show that the spectral characteristics of C60/PVP complexes vary depending on the PVP molecular mass and fullerene content in the complex. Therefore, the quantitative determination of fullerene concentration in such complexes by measuring their absorbance at 336 nm without extraction (Lyon et al., 2006) can give non-reliable results. For quantitative analysis of fullerene in such complexes we used the heterophase and homophase methods, based on destruction and isolation of pure fullerene C60 (Krakovjak et al., 2006). The choice of the method was determined by fullerene concentration - at concentration less... 

Certainly, it is not very good when fullerene concentration in C60/PVP complexes is rather low, but let us keep in mind that the acting antiviral dose of fullerene itself in this complex is not high. The active quantity of fullerene, calculated with the neglecting of the polymer vehicle, against the influenza vims is about 7pM (Piotrovskii et al., 2001). 

The derived formula (38) determines the dependence of free energy of bcc fullerite on temperature, fullerene concentrations, hydrogen content, its activity, and energetic constants. 

Figure 15 shows the plots of temperature dependence of hydrogen solubility in bcc phase, constructed for fullerenes concentrations Cj = 0,85, c2 =0,15 and for the different values of activity and energetic parameters. 

Since their discovery in 1985 [1] and subsequent isolation in macroscopic quantities [2], fullerenes and related forms of carbon such as nanotubes have been the subject of enormous numbers of both theoretical and experimental studies. This chapter describes a series of theoretical studies of fullerenes, concentrated on buckminsterfullerene, the original and still the most common form, which are tied together by an underlying valence bond picture of chemical structure. This work has attempted to identify characteristics of fullerenes which are more easily discerned in a valence bond than in a molecular orbital picture, and to see how far these valence bond ideas can be pushed before they break down. 

Electric conduction of the toluene-fullerene-ethanol (TFE) solution depends upon the electrical properties of ethanol. The volume of ethanol added to the solution has been varied between 10 and 50 vol. % at fullerene concentrations 1.5 2.8 mg-ml"1. In this case the operating current density (0.4-0.9 mA-cm"2) has been achieved at the potential difference between electrodes from 200 to 1600 V [13]. However a strong electric field between electrodes can produce change in electrical properties of the solution or cause degradation of some of its components. 

Fig. 5.5. Luminescence quenching (bullets, right hand, axis) and short-circuit current Ac (black squares, left hand axis) vs. molar fullerene concentration in a bulk hetero junction composite. The different onsets for percolation for the two phenomena (exciton diffusion versus ambipolar carrier transport) can be clearly seen...

The kinetic studies make use of the unequally sized reaction partners (e.g. a large electron donor and a small electron acceptor couple) and benefit from the low viscosity of dichloromethane (DCM), both of which elevate the diffusion-controlled limit. To study the electron transfer, deoxygenated DCM solutions of, for example, w-terphenyl at high concentrations (0.02 m) were irradiated in the presence of different concentrations of fullerene (ca 10 m) [62]. This resulted in accelerated decay of (arene) + UV-Vis absorption, with rates linearly depending on fullerene concentration [62]. Formation of the electron-transfer product, fullerene", was confirmed spectroscopically by measurement of the NIR fingerprint (Amax = 1080 nm) [62, 65]. 

Figure 15-4 shows the intensity of the photoluminescence as a function of the fullerene concentration in MDMO-PPV/PCBM composites. The strong quenching... 

Fig. 33 Tapping mode AFM images of P3HT PCBM films without (a, b) and with aluminum top electrode (c, d) at different PCBM concentrations. Large crystalline PCBM dendrites are observed for the larger fullerene concentration. (Reprinted with permission from [175], 2004, Institnte of Physics Publishing)...

The cluster formation is strongly dependent on the concentration of fullerene and the solvent mixture composition in a correlated fashion. For fullerene in toluene-acetonitrile mixtures, the higher the fullerene concentration, the lower the acetonitrile composition required for the observation of cluster formation [80,81]. 

Addition of various concentrations of [60]fullerene, for example, to a ZnTPP solution, resulted in an accelerated decay of the 7t-radical anion (ZnTPP "). The observed rate was linearly dependent on the [60]fullerene concentration, which, in turn, has led to the assumption that the ZnTPP tt-radical anion reacts with [60]fullerene. To confirm a probable electron transfer, the formation of the characteristic C60 absorption in the NIR ( ax = 1080 run) was also monitored. The grow-in rate of the C o " absorption at various wavelengths in the 980-1060 nm range was nearly identical to the decay rate of the MP absorption at 650-750 nm. For example, in the case of ZnTPP 7t-radical anion (ZnTPP "), a bimolecular rate constant of (2.5+1.0) x 10 M s was derived from the ZnTPP " decay (720 nm) and (1.4 1.0) x 10 M s from the Ceo formation (970 nm). These two values are in reasonable agreement and confirm unmistakably the electron transfer from the one-electron reduced metalloporphyrin (ZnTPP) to the singlet ground state of the fullerene ... 

In contrast, one-electron reduction of Cr "MSP, Ni"TPP, and Cu"TPP is known to occur at the metal center yielding Cr MSP, Ni TPP, and Cu tPP, respectively. Reduction of the metal center results in only minor spectral shifts of the metalloporphyrins Soret-and Q-bands, and lacks, in particular, the intense absorption in the 600-800 nm region. The decay of these species upon reaction with [60]fullerene was monitored in the 500 nm range, where the reduced metalloporphyrin absorbs more intensely than the parent compound. The rate constants for these reactions were derived from the linear dependence of the decay rate upon [60]fullerene concentration. 

To study the electron transfer from [60]fiillerene to the arene radical cation, deoxygenated DCM solutions of, for example, m-terphenyl were irradiated in the presence of variable [60]fullerene concentrations (0.7 - 6.0) x 10 M. The short life-time of some of the (arene)", in combination with the unfavorably high ionization potential of [60]fiillerene limited the ability to measure the electron transfer process to, however, only a few (arene) . Formation of the electron transfer product, namely, was confirmed spectroscopically by measuring the NIR fingerprint at > max= 980 nm, which resembles that found upon direct oxidation of [60]fullerene. 

Similar to the [60]fullerene case, addition of [76]fullerene and [78]fullerene in the 10 M concentration range resulted in an accelerated decay of the arene radical cation s UV-VIS absorption, with rates linearly depending on the fullerene concentration. At the same time, formation of the fullerene radical cations became observable in the NIR... 

Solutions without Pc gave very weak luminescence at 7(X) nm, detected only when high fullerene concentrations and laser intensities were used. Addition of as little as 10 M Pc increased the intensity by an order of magnitude. Increasing the Pc concentration caused a further increase in intensity. The lifetime of the 700 nm luminescence was shorter than that at 1270 nm by a factor of 2 Fig. 1 shows the relationship in similar lifetime relationships occur in solvents with a wide range of singlet oxygen lifetimes and in the presence and absence of quenchers (Fig. 2). In all cases, the intensity at 700 nm was... 

It should be noted that even at a low energy of implanted species (100 keV) the size of nanopores that are formed in the implanted layer turns out to be enough to make the insertion of large molecules possible (for instance, the dicarbollyl complex of cobalt readily diffuses into polyethylene implanted with 150-keV ions [75]). In the case of energetic ions (with energies of several hundreds of MeV), the pore size increases and the implanted polymer can be doped with fullerenes [61]. Thus, the concentration of C o molecules that difhise into polyimide implanted with 500-MeV ions from toluene solution amounts to as much as 1.8 x 10 fullerene molecules per track (the fullerene concentration was evaluated by a neutron depth profiling technique using Li ions, known to form the insoluble adduct with Cfio as the tracer [61]). 

TABLE 1.1 Changes of Molar Absorption Coefficients Depending on Mono-Substituted 1,2-Dihydro-C -Fullerenes Concentration... 

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