Perets Yu. S.


Electrophysical and thermal properties of polymer composite materials with two-component filler.
01.04.07 – solid state physics
Doctor of Philosophy degree (Candidate of science in Physics and Mathematics)

Thesis for a Doctor of Philosophy degree (Candidate of science in Physics and Mathematics) by specialty 01.04.07 – Solid state physics. – Taras Shevchenko National University of Kyiv, MES of Ukraine, Kyiv, 2014.
The thesis is devoted to the investigation of the electrophysical and thermal properties of composite materials (CMs) with different types of carbon fillers and CMs with binary filler.
In the process of research the methods of fabrication of the ultrathin graphite nanoplatelets (GNPs) and polymer composite materials with two-component filler were developed. The changes in shape, size and morphology of the particles after functionalization thermoexfolited graphite have been studies by the methods of optical and electron microscopy. It was revealed that functionalization of thermoexfolited graphite leads to the destruction of the original structure of the particles of thermoexfolited graphite and reducing their sizes up to several nanometers.
The influence of the different types of nanocarbon and two-component filler on the transport characteristics of the CMs was analyzed. It is shown that using GNPs and carbon nanotubes (CNTs) as fillers makes it possible to obtain the composite materials with a low percolation threshold, and the addition of dielectric filler leads to a decrease of percolation threshold and an increase of the electrical conductivity and thermal conductivity in these CMs. Within the framework of model of the effective conductivity it is shown that in a case of the addition of the dielectric filler in CM polymer –nanocarbon with a chain structure of nanocarbon filler particles the improvement of electrophysical characteristics is related to a decrease of contact resistance between filler particles Rk, while in CM with highly branched skeleton structure of filler particles these changes are associated primarily with the increase of the number of the conductive chains.
It is shown that the thermal conductivity of epoxy-based CMs strongly depends on the structural and morphological characteristics of carbon fillers, the character of their distribution in the polymer matrix, and their orientation with respect to the heat flow in CM. The lower value of thermal conductivity of CMs MWCNT-epoxy in comparison with CMs GNP-epoxy can be explained by a significantly higher value of thermal contact resistance Pk between nanotubes in a chain in comparison with the value Pk for GNPs. It is established that the adding of BN particles in the CMs with carbon filler greatly enhances the effect of increasing the thermal conductivity of the epoxy matrix with increa-sing the content of carbon nanofillers.The models of the AC and DC conductivity and thermal conductivity of composite materials were proposed. The concentration and tempe-rature dependencies of the electrical and thermal conductivities which have been calcula-ted according to the proposed models are in good agreement with the experimental results.
Keywords: nanocarbon, boron nitride, barium hexaferrite, polymer composites with binary filler, AC and DC conductivity, thermal conductivity.

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