Study on the Curie Transition of P(VDF-TrFE) Copolymer

• Main Authors: Devi Eka SeptiyaniArifin, 阿芬朵維
• Other Authors: Jr-Jeng Ruan
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/2t2u8r

碩士 === 國立成功大學 === 材料科學及工程學系 === 104 === A systematic study was carried out to decipher the mechanism of Curie transition of piezoelectric crystals of poly(vinylidene fluoride trifluoroethylene) P(VDF-TrFE). The unique polarity of P(VDF-TrFE) crystalline phase below curie transition temperature is attributed to the lattice packing of all-trans molecular chains, which allocates all the substituted fluorine atoms on one side of molecular chains and hydrogen atoms on the other side. Therefore a net dipole moment is created across the lateral packing of molecular chains. Nevertheless, due to the mutual repulsion among fluorene atoms, this all-trans conformation is not stable, and ready to change above Curie temperature, where thermal kinetic energy is sufficient to cause segmental rotation. As being illustrated by in-situ recorded X-ray diffraction and thermal analysis, the concerned curie transition is deciphered as a two-step process different from conventional one-step solid-solid transitions. The lattice expansion and change of molecular conformation are derived to take place first and appears as a progressive process, which is followed by the thermal axial rotation of molecular stems within lattice packing. This thermal axial rotation of molecular stems is similar to what has been found in plastic crystals. Accompanied with this two-step process during heating, the occurrence of lamellar bending is inferred for elucidating the decline of stacking regularity of crystalline lamellae, which reversibly recover during subsequent cooling. However, as the crystalline lamellae of P(VDF-TrFE) are confined in between the stacking of crystalline lamellae of PVDF, lamellar bending is restricted accordingly. As a result, a certain fraction of the piezoelectric crystalline lamellae were found to survive through the Curie transition. Thus, in addition to the suggestion of a two-step process as a new concept for understanding the Curie transition, the relationship between the lamellar stacking and transition of molecular packing is unveiled as well in this research.