Highly enhanced dielectric constants of barium titanate-filled polymer composites using polymer-grafted carbon nanotube matrix

The dielectric property of a composite system of poly(cyclohexyl methacrylate) grafted on multi-walled carbon nanotubes (PCHMA-CNT) and barium titanate (BT) powder was systematically characterized over the broad frequency range of 10–2–106 Hz. PCHMA-CNT served as a polymer matrix in the PCHMA-CNT/BT system. Because of the high dielectric constant εr’ and the quite low dissipation factor (tanδ) of the PCHMA-CNT matrix, the PCHMA-CNT/BT composites exhibited much higher εr’ than conventional BT-filled PCHMA composites (PCHMA/BT) with the tanδ low. The εr’ of PCHMA-CNT/BT was well consistent with the predicted one by Lichtenecker’s logarithmic mixing rule at high BT loading whereas smaller than the predicted value at low BT loading. This is because each BT particle tended to be isolated by the PCHMA-CNT matrix at the low BT loading in the PCHMA-CNT/BT system. The explanation was strongly supported by the results for the εr’ of a BT particle-isolated model system (PCHMA-BT), where the PCHMA chains were grafted on the BT particles in order to compel to isolate the BT particles each other