C60one- and two-dimensional polymers, dimers, and hard fullerite: Thermal expansion, anharmonicity, and kinetics of depolymerization

Abstract

We report on high-resolution thermal expansion measurements of high-temperature-pressure treated C 60 ͓one-dimensional ͑1D͒ and ͑2D͒ polymers and ''hard fullerite''͔, as well as of C 60 dimers and single crystal monomer C 60 between 10 and 500 K. Polymerization drastically reduces the thermal expansivity from the values of monomeric C 60 due to the stronger and less anharmonic covalent bonds between molecules. The expansivity of the ''hard'' material approaches that of diamond. The large and irreversible volume change upon depolymerization between 400 and 500 K makes it possible to study the kinetics of depolymerization, which is described excellently by a simple activated process, with activation energies of 1.9Ϯ0.1 eV ͑1D and 2D polymers͒ and 1.75Ϯ0.05 eV ͑dimer͒. Although the activation energies are very similar for the different polymers, the depolymerization rates differ by up to four orders of magnitude at a given temperature, being fastest for the dimers. Preliminary kinetic data of C 70 polymers are presented as well.

Stability at high temperature and decomposition kinetics of the fullerene dimers and photopolymers

“…The experimental data exhibit a good linear dependence in logarithmic scale, yielding an activation energy of E A = (1.71 ± 0.06) eV/molecule. This value is close to the E A = (1.75 ± 0.05) eV/molecule obtained from the X-ray thermal expansion studies of powdered dimeric samples, synthesized by a solid-state mechanochemical reaction of C 60 with potassium cyanide, as well as to the activation energy E A = (1.9 ± 0.1) eV/molecule of the 1D and 2D polymers decomposition [9]. It is interesting to compare these data with the decomposition kinetics of fullerene photooligomers (C 60 ) n .…”

“…The constant A, related to the characteristic phonon frequency, is measured in time units [9]. The corresponding Arrhenius plot is included in the Fig.…”

“…The decomposition kinetics of polymers was studied by X-ray thermal expansion and Raman measurements [7,9]. In the case of photopolymers, the small amount of the photo-transformed material on the surfaces of samples makes the DSC and X-ray measurements inappropriate, so the Raman spectroscopy becomes a unique tool in the study of the photopolymer decomposition.…”

Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures

“…Because the sample is a mixture of all chiralities, the average α d should also be very similar to the average axial expansion coefficient of the tubes. The thermal expansion of a bundle should thus probably be dominated by α g , which should be similar to the out-of-plane thermal expansion of graphite or, considering the curvature, to the thermal expansion of fullerenes or linear fullerene polymers [26].…”

Microstructure, nucleation and thermal properties of high-pressure crystallized MWCNT/nylon-6 composites

“…As an example, the fullerene C 60 shows both glass and phase transitions under pressure [1]. It can be irreversibly cross-linked into various polymeric structures [2] and it has been reported to form super-hard carbon structures under pressure [3]. In the cases of polymers and their composites, HP&HT treatments are particularly useful for irreversibly changing two of the most important polymer characteristics:…”