Synergistic Improvement in γ-Phase Content and Dielectric Properties of PVDF/Deep Eutectic Solvent/Montmorillonite Composite Films

The high dielectric constant of PVDF is very important for its high-performance energy storage dielectrics, but it is more critical to strike a proper balance between high dielectric constant and low dielectric loss. In this work, deep eutectic solvent (DES) and montmorillonite (MMT) have been used together to prepare γ-phase PVDF composite films with excellent dielectric properties. It is found that DES significantly induces crystallization of γ-phase and increases the dielectric constant of the composite due to the incremental ion motion. Meanwhile, DES greatly promotes the stripping and dispersion of MMT layers, which in turn inhibits the long-range ion migration and therefore suppresses the dielectric loss of the composite to a very low level. The dielectric constant of PVDF/MMT/DES composite films can increase to 32, while the dielectric loss remains as low as 0.06 at 1 kHz. Moreover, the synergistic effect of MMT/DES also contributes to enhancing the toughness and optical transmittance of composite films.