skip to main content

Search for: All records

Creators/Authors contains: "Zhu, Lei"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Free, publicly-accessible full text available April 21, 2023
  2. Free, publicly-accessible full text available February 24, 2023
  3. Free, publicly-accessible full text available February 24, 2023
  4. Free, publicly-accessible full text available November 9, 2022
  5. Abstract Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with | d 33  | < 30 pC/N. We prepare a highly piezoelectric polymer ( d 33  = −62 pC/N) based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals are achieved, which show a high spontaneous polarization ( P s ) of 140 mC/m 2 . Given the theoretical limit of P s,β  = 188 mC/m 2 for the neat β crystal, the high P s cannot be explained by the crystalline-amorphous two-phase model (i.e., Pmore »s,β  = 270 mC/m 2 ). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d 33 for the poled BOPVDF. The plausibility of this conclusion is supported by molecular dynamics simulations.« less
    Free, publicly-accessible full text available December 1, 2022
  6. Free, publicly-accessible full text available November 1, 2022
  7. Poly(vinylidene fluoride) (PVDF) and its random copolymers exhibit the most distinctive ferroelectric properties; however, their spontaneous polarization (60–105 mC m −2 ) is still inferior to those (>200 mC m −2 ) of the ceramic counterparts. In this work, we report an unprecedented spontaneous polarization ( P s = 140 mC m −2 ) for a highly poled biaxially oriented PVDF (BOPVDF) film, which contains a pure β crystalline phase. Given the crystallinity of ∼0.52, the P s for the β phase ( P s,β ) is calculated to be 279 mC m −2 , if a simple two-phase modelmore »of semicrystalline polymers is assumed. This high P s,β is invalid, because the theoretical limit of P s,β is 185 mC m −2 , as calculated by density functional theory. To explain such a high P s for the poled BOPVDF, a third component in the amorphous phase must participate in the ferroelectric switching to contribute to the P s . Namely, an oriented amorphous fraction (OAF) links the lamellar crystal and the mobile amorphous fraction. From the hysteresis loop study, the OAF content was determined to be ∼0.28, more than 50% of the amorphous phase. Because of the high polarizability of the OAFs, the dielectric constant of the poled BOPVDF reached nearly twice the value of conventional PVDF. The fundamental knowledge obtained from this study will provide a solid foundation for the future development of PVDF-based high performance electroactive polymers for wearable electronics and soft robotic applications.« less