Filler size effects on the microstructure and properties of polymer-ceramic nanocomposites using a semicrystalline matrix

Size effects of ceramic nanofiller on polymer-ceramic nanocomposites in terms of microstructure and related properties were studied using P(VDF-CTFE) matrix filled with BaTiO₃ (BTO) nanoparticles in the sizes of 50, 100, 150, and 200 nm respectively. The experimental results show that the dielectric constant (ε_r) of the P(VDF-CTFE)-BTO nanocomposites significantly increases with increasing size of the nanofiller. Based on Lichtenecker’s mixing law, the ε_r of the BTO nanoparticles was calculated from the ε_r of the nanocomposites and the results indicate that the ε_r of the BTO nanoparticles increases with increasing size from 50–200 nm. The XRD and DSC results suggest that the crystals of P(VDF-CTFE) matrix are of α and γ phases, and the presence of BTO nanofiller favors the formation of the γ phase. Regarding the dielectric responses associated with the chain movement of a polar matrix, the smaller the nanofiller the stronger the influence on the mobility of polymer segments (i.e., glass transition), while the larger the nanofiller the higher the mobility of long polymer chains at high temperatures. Lichtenecker’s mixing law was also used to calculate the ε_r of the BTO nanoparticles from the ε_r of the nanocomposites at different temperatures. It is found that the applicability of a mixing law used in the polymer-ceramic nanocomposites is strongly related to the dielectric loss of the polymer matrix that is associated with the mobility of polymer chains for the polar polymers, especially at high temperatures. In addition, the dielectric strength (E_b) decreases significantly with increasing size of the nanofiller while the polarization under a same electric field does not change much, which experimentally suggests that smaller ceramic nanofiller is preferred to obtain a high E_b.