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Abstract
This study investigates the effect of different cooling rates on the dielectric constant and loss tangent of a system of TiO2 nanoparticles dispersed in a PVC matrix. Experimental results show that at high frequencies, the dielectric loss tangent of nanocomposites increases sharply due to the increased energy dispersions at high frequencies and a sharp increase in alternating electrical conductivity. On the other hand, the sharp decrease in dielectric constant is explained by the decrease in the polarizing ability of nanocomposites at high frequencies. It was found that for PVC/3%TiO2 based nanocomposites photoluminescence intensity strongly changes depending on the temperature-time mode of crystallization. PL intensity at all wavelengths increases sharply at the cooling rate of film β1 = 2°/min, as compared with the samples obtained at the cooling rate of β2= 200°/min and in the case of cooling rate β3 = 2000°/min. The increase of PL intensity depending on the β is explained by the fact that the supramolecular structure of the polymer changes forming large crystallites in the polymer, resulting in stronger interfacial interaction between the nanoparticles and the matrix which in turn increases the luminescence intensity. SEM images indicated that for the samples obtained at different cooling rates, the size of TiO2 nanoparticles are practically unchanged, but the supramolecular structure of the matrix changes.