Application of a Coupling Agent to Improve the Dielectric Properties of Polymer-Based Nanocomposites

It was proved that the using of commercial coupling agent could modify the surface of ceramic nanofillers, therefore, good wettability on the ceramic-polymer interface was achieved, and the enhanced energy storage performances were obtained by a suitable amount of coupling agent. The method developed by this work could be used in the preparation of flexible composites, which is highly desirable for the production of high-performance film capacitors. Prepare the solution of KH550 with 95 weight percent ethanol water solvent by 15 minutes ultra-sonication.

Treat the BT nanoparticles in KH550 solutions by 30 minutes ultra-sonication. In this process, measure the weights of KH550 and BT nanoparticles fillers coated with one, two, three, four, and five weight percent of coupling agent in the KH550 dilute solution with a volume of five milliliter. Evaporate the water-ethanol solvent from the matrix at 80 degrees C for five hours, and then to 120 degrees C for 12 hours in a vacuum oven.

Use the dry nanoparticles as the surface modified fillers in the preparation of BTVC-91 nanocomposites. One, the DMF-based polymer solution was prepared by dissolving 0.3 grams of polymer powders in 10 milliliter DMF at room temperature by a magnetic stirring for eight hours. Two, the barium titanate nanoparticles were added into the solution, then followed with 12 hours stirring to form homogeneous suspension and ultrasonicated for 30 minutes.

In the preparation process, both the unmodified barium titanate and the barium titanate coated with coupling agent were used. After that, the suspension was cast on a preheated class substrate to make films. Three milliliters of the suspension was dropped on each of the glass substrate.

Five, the glass substrate with suspensions was then kept in the oven at 70 degree for eight hours to evaporate the solvent. Six, finally, the as-cast films were released from the glass substrate and obtained free-standing films were annealed at 160 degrees C in air for 12 hours. The free-standing nanocomposite films was successfully fabricated according to the protocol.

It was confirmed from the SEM that the ceramic nanoparticles treated with a suitable amount of coupling agent that could be uniformly distributed in the nanocomposites during casting;while the excessive amount of coupling agent may cause interactions between ceramic nanoparticles and leading to the aggregation of fillers. For the nanocomposites with low filler content, the dielectric constant of the composites was basically unchanged with a small amount of coupling agent is used and slightly decreases with the future increasing coupling agent amount. For the nanocomposites with high filler content, the dielectric constant of the composites increase adversely with a small amount of coupling agent and sharply decrease with the future increasing coupling agent amount.

In terms of dielectric loss, the nanocomposites with coupling agent have a higher dielectric loss than the nanocomposites without coupling agent. The maximal breakdown strengths was obtained when two weight percent of coupling agent was used. A lower breakdown strengths was found from the nanocomposites with a higher amount of coupling agent.

Due to the enhanced breakdown strengths and our relatively high charge discharge efficiency, the maximal energy density of the nanocomposites with a small amount of coupling agent were improved. In this work, barium titanate, the most widely studied ferroelectric material with high dielectric constant were used as fillers. The PVDF-CTFE copolymer was used as a polymer matrix for the preparation of ceramic polymer composites.

To modify the surface of barium titanate nanofillers, the commercially available KH550 were purchased and used as coupling agent. They critical amount of the nanocomposite system was determined by the series of experiment. An easy, low-cost, and the widely applicative method to improve the energy density of nano-sized composite system was demonstrated.