Influence of coupling agent on the microstructure and dielectric properties of free-standing ceramic-polymer composites

The influence of a commercial coupling agent on the dielectric properties and microstructure of ceramic-polymer nanocomposites are studied. Free-standing BaTiO _3 -P(VDF-CTFE) films were fabricated using a simple solution-casting process, and the good wettability between fillers and polymer matrix was obtained by using 3-Aminopropyltriethoxysilane as coupling agent. It is found that the coating of a small amount of coupling agent on the surface of BaTiO _3 fillers results in an enhanced dielectric constant, a higher breakdown strength and a larger energy-storage efficiency. When an excessive amount of coupling agent was used, the non-attached coupling agent molecules participated in the complex reactions and result in the aggregation of fillers and the reduction of dielectric constant. It is also found that the surface modification of fillers has a complicated influence on its dielectric behavior which leads to an increase in the dielectric loss of the nanocomposites. When an appropriate amount of coupling agent is coated on fillers, the energy storage density of the nanocomposite is improved due to the enhanced dielectric constant and higher breakdown strength. A maximal discharged energy-storage density of about 4.0 J cm ^−3 was obtained from the nanocomposite film containing 15 vol% of surface modified BaTiO _3 fillers with 1 wt% of KH550, which is about 3 times of that for the nanocomposite without coupling agent.