Induced formation of dominating polar phases of poly(vinylidene fluoride): positive ion-CF2 dipole or negative ion-CH2 dipole interaction.

The "ion-dipole" interaction has been the most widely accepted mechanism for the direct formation of polar phases (β, γ) of poly(vinylidene fluoride) (PVDF), which have been widely used as transducers, actuators, and sensors. However, the type of charged ions is still controversial. In order to throw light upon this issue, two types of charged small organic molecules that are in different physical states (melt or solid) during the crystallization of PVDF were melt-blended with PVDF resin. Results revealed that only the incorporation of positive charged molecules can lead to the formation of polar phases. Additionally, it is interesting to find that during the crystallization of PVDF, molten positively charged molecules resulted in β-phase dominating, while solid positively charged molecules exclusively induced γ-phase. These results lead to the understanding that the induced formation of polar phases of PVDF is due to the "positive ion-CF2 dipole" interaction.