Kyzyma O. Dynamics of fullerene C60 cluster formation in the polar solvents

The thesis concerns the research of cluster formation in a liquid system of fullerenes based on polar solvents as observed by small-angle neutron scattering (SANS), mass-spectroscopy and UV-Vis spectroscopy. The main attention is paid to investigation of influence of water addition in the C60-N-methyl-2-pyrrolidone (C60-NMP) system on the structure of fullerene clusters and research of the stabilization mechanism of fullerene cluster in polar solution. Absorption spectra were obtained using Shimadzu UV-2401PC and Hitachi U-2000 UV/Vis spectrophotometers. Laser desorption/ionization time-of-flight mass spectrometry was used for ion production. Measurements were conducted using the Bruker Daltonics Autoflex II instrument. SANS experiments were performed on the small-angle diffractometers at the IBR-2 pulsed reactor of the Joint Institute for Nuclear Research, Dubna, Russia, and at the research steady-state reactor of the Budapest Neutron Centre, Hungary. The effect of cluster reorganization in the systemC60-NMP after addition of water was observed by small-angle neutron scattering and mass spectroscopy. Results of the SANS experiments indicate that large stable clusters in the C60-NMP solution are partially dissociate into smaller ones with the addition of water. The effect has a sharp character when the water content in the system approaches 40 vol. %. This effect depends on the time interval between preparation of C60-NMP solution and its dilution with water: the size of the clusters formed in the final C60-NMP-H2O solution increases with the age of initial C60-NMP solution. A change in UV-Vis spectrum with time (temporal solvatochromic effect) within one month after preparation of the C60-NMP system and sharp solvatochromic effect after water addition to the fresh C60-NMP system were observed. When water was added into the system C60-NMP, solvatochromic effect took place depending on the time interval between the preparation of the initial C60-NMP solution and the addition of water. The most pronounced changes in the UV-Vis spectrum took place if water was added to the fresh C60-NMP solution. The growth of scattering particles in the C60-NMP system leads to an increase in the Mie scattering contribution into the absorption spectrum. Estimation of the Mie scattering contribution into the UV-Vis spectrum was performed. The results of the calculations showed that the Mie scattering contributes insignificantly to the UV-Vis spectrum. Therefore the changes in the UV-Vis spectrum are due to absorption, which relates to electronic state of fullerene molecules. The mass-spectroscopy investigations of the C60-NMP system are showed that fullerenes form large scale clusters with strong bonds between molecules with time. The addition of water in this system leads to the decomposition of fullerene clusters in the solutions. It should be noted that dilution of the old (age more than 1 month) C60-NMP system results in appearing of monomer peak whereas small fullerene clusters (up to 13 monomers in the cluster) were not observed. This fact indicates that the decomposition of clusters in the solutions occurs as a result of the monomer detachment. The investigation of the coagulation process in the liquid system water-fullerene C60 revealed strength stabilizing water shell, which is formed on the surface of the fullerene clusters.