Self-organization of ferroelectric polymer crystals and enhanced dielectric responses

Abstract For the ferroelectric polymer, poly (vinylidenefluoride-co-trifluoroethylene)(PVDF-TrFE), the enhanced secondary crystallization above Curie temperature has been evaluated able to prevailingly yield drawing effects on dangling chains of dispersed crystals, and thus results in crystal association and sequential coalescence. Multiple thickening of lamellar crystals and in-between amorphous regions are identified therefore. As the balance of mutual drawing among evolving crystals is able to be gradually reached, rarely recognized self-regulated assembly of polymer crystals occurs, which eventually led to several-micrometer spread of oriented stacking arrays of lamellar crystals. As a result, considerable in-between molecular segments are enduringly stretched, and aligned electric dipoles are thus widely created by applied electric fields. The dipolar polarization of both ferroelectric crystals and stretched molecular segments surprisingly makes films less than 80 nm thick yields the record dielectric constant of 84 at room temperature. As the self-regulated crystal assembly is precluded, much lower thin-film dielectric constants and higher dissipation factors are yielded instead, although similar crystallinity and alignment of dipolar polarization have been attained. The persistent stretching of molecular segments related to unveiled crystal self-organization is thus understood as a new direction to create superior directional dipolar polarization, and thus to substantially improve dielectric properties of polymer materials.