Effect of processing factors on dielectric properties of BaTiO3/hyperbranched polyester core-shell nanoparticles

In our recent publication we have demonstrated that BaTiO₃/hyperbranched polyester/methacrylate hybrid nano-particles, with a filler fraction of 41 wt.% first dissolved in 2-butoxyethanol and crosslinked during 3 hours (at 125°C), exhibited highly promising dielectric constant as high as 85 at 1kHz. On the other hand, when the same hybrid nanoparticles have been diluted in methyl methacrylate (MMA) and then cured for 12 hours at the same temperature the permittivity of the material decreased significantly and reached 5 at 1 kHz. In the present work we have studied how processing factors, such as the employed diluent and crosslinking duration, affect the dielectric properties of the core-shell nanoparticles. In our first set of experiments we have studied the electrical properties of capacitors fabricated using the solution of hybrid nanoparticles diluted in 2-butoxyethanol. Curing has been monitored for 13 hours at 125°C. We have determined that the duration of thermal curing has a significant effect on dielectric properties of BaTiO₃/hyperbranched polyester/methacrylate nanocomposites. In the second set of experiments the diluent influence on the properties of hybrid nanoparticles was investigated. As had been expected, dielectric constants of particles diluted in MMA were lower than those of hybrid particles diluted in 2-butoxyethanol. The origin of this phenomenon was determined by comparing the chemical behavior of the diluents under thermal curing. 2-butoxyethanol characterized by a boiling point of 170°C was evaporated during the thermal curing process. Despite the boiling point of 100°C, MMA polymerization is predominant upon evaporation, and leads to the decrease in the initial filler fraction. This explanation has been validated by measuring the weight losses of samples oven-dried at 125°C for 13 hours. We discuss in detail the experimental data and results, as well as their use in understanding- the basic physical mechanisms underlying the observed electrical behaviors of hybrid nanoparticles.