Identification of mutual polarization between dispersed inorganic crystals and surrounding ferroelectric polymer crystals
In our recent research interests, ferroelectric polymer, poly (vinylidenefluoride-co-trifluoroethylene)(PVDF-TrFE), are able to evolve unique polar crystalline phase below curie transition temperature via the lattice packing of all-trans conformers, which allocates most of substituted fluorine atoms on one side of molecular segments and hydrogen atoms on the other side.Therefore, PVDF-TrFE with intrinsic electric fields enable to explore the mutual interaction among different materials, such as ZnO. As the piezo-response of PVDF-TrFE lamellae near ZnO nanorods greatly increase, we suggest that mutual polarization effect is involved.
After annealing, the PVDF-TrFE lamellar crystals are developed as shown on TEM images left. When the annealing temperature increases, the segregation of PMMA will occur since PMMA molecules cannot participate in the crystal growth of PVDF-TrFE. The redistribution and the formation of PMMA domains with a relatively uniform size can be observed. In addition, PMMA domains will increase at higher annealing temperature, due to the strong aggregation tendency of zinc acetate crystals coated by PMMA.
As annealing time increase at 130 °C, the arrangement of PVDF-TrFE lamellar crystals can be achieved, as shown on TEM images right. After the hydrothermal process, the distribution of ZnO nanorods among PVDF-TrFE network is developed, as shown on SEM images right. Upon annealing at 130 °C, the aggregation tendency of the precursors will be decreased. Therefore, the precursors of ZnO can diffuse into the amorphous regions among the lamellar crystals, so called the entropy-driven process, and then obtain uniformly distributed organic-inorganic hybrid thin films.
Mutual polarization of PVDF-TrFE and ZnO nanorods
As only the PVDF-TrFE areas are selected, the tremendous value of piezoelectric constant is identified. The involved effect of mutual polarization is considered and therefore enhance the piezo-response of PVDF-TrFE. The extent of mutual interaction will decrease with the distance between nanorods region and PVDF-TrFE lamellae region increase.
Point A
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Point E
Pristine PVDF-TrFE
Evolved ZnO nanorods are illustrated to have opposite polarization orientations compared with that of surrounding PVDF-TrFElamellar crystals, which means the dipole moments of ZnO nanorods are opposite to that of lamellae. Together with the increase of piezoelectric responses, mutual polarization between dispersed crystals has been further unveiled therefore.