Ion-Boosting the Charge Density and Piezoelectric Response of Ferroelectrets to Significantly High Levels

Ion-Boosting the Charge Density and Piezoelectric Response of Ferroelectrets to Significantly High Levels

Wang, Ningzhen (University of Connecticut)
van Turnhout, J. (TU Delft Team Jilt Sietsma)
Daniels, Robert (University of Connecticut)
Wu, Chao (University of Connecticut)
Huo, Jindong (University of Connecticut)
Gerhard, Reimund (University of Potsdam)
Sotzing, Gregory (University of Connecticut)
Cao, Yang (University of Connecticut)

2022

In contrast to molecular-dipole polymers, such as PVDF, ferroelectrets are a new class of flexible spatially heterogeneous piezoelectric polymers with closed or open voids that act as deformable macro-dipoles after charging. With a spectrum of manufacturing processes being developed to engineer the heterogeneous structures, ferroelectrets are made with attractive piezoelectric properties well-suited for applications, such as pressure sensors, acoustic transducers, etc. However, the sources of the macro-dipole charges have usually been the same, microscopic dielectric barrier discharges within the voids, induced when the ferroelectrets are poled under a large electric field typically via a so-called corona poling, resulting in the separation and trapping of opposite charges into the interior walls of the voids. Such a process is inherently self-limiting, as the reverse internal field from the macro-dipoles eventually extinguishes the microdischarges, resulting in limited density of ions and not too high overall piezoelectric performance. Here, a new method to form ferroelectrets with gigantic electroactivity is proposed and demonstrated with the aid of an external ion booster. A laminate consisting of expanded polytetrafluoroethylene (ePTFE) and fluorinated-ethylene-propylene (FEP) was prefilled with bipolar ions produced externally by an ionizer and sequentially poled to force the separation of positive and negative ions into the open fibrous structure, rendering an impressive piezoelectric d33 coefficient of 1600 pC/N an improvement by a factor of 4 in comparison with the d33 of a similar sandwich poled with nonenhanced corona poling. The (pre)filling clearly increases the ion density in the open voids significantly. The charges stored in the open-cell structure stays at a high level for at least 4 months. In addition, an all-organic nanogenerator was made from an ePTFE-based ferroelectret, with conducting poly(3,4-ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) coated fabric electrodes. When poled with this ion-boosting process, it yielded an output power twice that of a similar sample poled in a conventional corona-only process. The doubling in output power is mainly brought about by the significantly higher charge density achieved with the aid of external booster. Furthermore, aside from the bipolar ions, extra monopolar ions can during the corona poling be blown into the open pores by using for instance a negative ionic hair dryer to produce a unipolar ePTFE-based ferroelectret with its d33 coefficient enhanced by a factor of 3. Ion-boosting poling thus unleashes a new route to produce bipolar or unipolar open-cell ferroelectrets with highly enhanced piezoelectric response.

bipolar and unipolar charging
corona charging
ePTFE ferroelectret
ion boost
piezoelectric response
wearable energy harvester

http://resolver.tudelft.nl/uuid:49663411-1fa3-4294-89ea-cd80664dc6cc

https://doi.org/10.1021/acsami.2c12185

2023-03-13

1944-8244

ACS applied materials & interfaces, 14 (37), 42705-42712

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2022 Ningzhen Wang, J. van Turnhout, Robert Daniels, Chao Wu, Jindong Huo, Reimund Gerhard, Gregory Sotzing, Yang Cao