Improving Dielectric Properties and Thermostability of CaCu₃Ti₄O₁₂/Polyimide Composites by Employing Surface Hydroxylated CaCu₃Ti₄O₁₂ Particles

Surface hydroxylation was implemented on CaCu3Ti4O12 (CCTO) particles to improve their interface compatibility and dispersibility in polyimide matrix. The surface hydroxylated CCTO fillers (CCTO–OH) were obtained by treating the CCTO particles in the mixed solution of H2SO4 and H2O2. The experimental results showed that the CCTO–OH/polyimide (PI) composite films had higher dielectric permittivity and lower coefficient of thermal expansion (CTE) compared to those of the CCTO/PI composite films, which were mainly attributed to the good dispersion of CCTO–OH particles and the enhanced interfacial polarization between CCTO–OH particles and PI chains. Among these CCTO–OH/PI composite films, the composite film with 40 vol % CCTO–OH particle loading exhibited the highest dielectric permittivity (76.9, 102 Hz), and a low dielectric loss (0.2, 102 Hz) was maintained. The maximum discharge energy density of the CCTO–OH/PI composite film with 25 vol % CCTO–OH reached 1.31 J/cm3, which was almost twice that of pure PI (0.63 J/cm3). Further, the prepared CCTO–OH/PI composite films had excellent heat resistance and low CTE. The high-k property of the CCTO–OH/PI composites remained stable up to 300 °C, which is probably the most heat-resistant dielectric material reported in the literature and is absolutely critical for the manufacture of electronic devices facing extreme conditions.