Structure and electrophysical properties of materials based on nanoparticles of oil asphaltenes

Abstract

This paper is a generalization of the authors’ works in the field of asphaltene physics fulfilled in recent years. Specific features of the "insulator-semiconductor" phase transition in high-boiling hydrocarbon fractions are discussed. It is shown that the active resistance of the samples decreases with heating to (65 - 85)0 C. At the same time, the concentration of paramagnetic centers increases, which is confirmed by the EPR. The growth of electrical conductivity in high-boiling hydrocarbon fractions containing asphaltenes is caused by the temperature generation of charge carriers - free radicals (spins) formed as a result of the rupture of weak carbon-carbon bonds in molecules weakened by conjugation with aromatic rings. The energy of rupture of such bonds is rather low and can be as low as 40 kJ/mol. All these facts confirm the hypothesis of the authors that in the samples a phase transition occurs from the "insulator" state to the "semiconductor" state. The dielectric-semiconductor phase transition is also due to the generation of stable free radicals, since they are strong electron acceptors and reduce the width of the forbidden band of the material. Quantum-chemical calculations confirm this hypothesis. In addition, quantum-chemical calculations of the supramolecular, molecular, and electronic structure of asphaltene nanoparticles have been carried out. An experimental study of asphaltene crystallites by the AFM method was carried out. Theoretical calculations are reasonably confirmed by the AFM data.