Dielectric behaviour of plasma hydrogenated TiO₂/cyanoethylated cellulose nanocomposites

The interface between the polymer and nanoparticle has a vital role in determining the overall dielectric properties of a dielectric polymer nanocomposite. In this study, a novel dielectric nanocomposite containing a high permittivity polymer, cyanoethylated cellulose (CRS) and TiO₂ nanoparticles surface modified by hydrogen plasma treatments was successfully prepared with different weight percentages (10%, 20% and 30%) of hydrogenated TiO₂. Internal structure of H plasma treated TiO₂ nanoparticles (H-TiO₂) and the intermolecular interactions and morphology within the polymer nanocomposites were analysed. H-TiO₂/CRS thin films on SiO₂/Si wafers were used to form metal-insulator-metal (MIM) type capacitors. Capacitances and loss factors in the frequency range of 1 kHz to 1 MHz were measured. At 1 kHz H-TiO₂/CRS nanocomposites exhibited ultra-high dielectric constants of 80, 118 and 131 for nanocomposites with 10%, 20% and 30% weight of hydrogenated TiO₂ respectively, significantly higher than values of pure CRS (21) and TiO₂ (41). Furthermore, all three H-TiO₂ /CRS nanocomposites show a loss factor <0.3 at 1 kHz and low leakage current densities (10^-6 A cm^-2-10^-7 A cm^-2). Leakage was studied using conductive atomic force microscopy (C-AFM) and it was observed that the leakage is associated with H-TiO₂ nanoparticles embedded in the CRS polymer matrix. Although, modified interface slightly reduces energy densities compared to pristine TiO₂/CRS system, the capacitance values for H-TiO₂/CRS-in the voltage range of -2 V to 2 V are very stable. Whilst H-TiO₂/CRS possesses ultra-high dielectric constants (>100), this study reveals that the polymer nanoparticle interface has a potential influence on dielectric behaviour of the composite.