Highly Efficient Piezoelectrets through Ultra-Soft Elastomeric Spacers.

Heinz Von Seggern,Sergey Zhukov,Claas Hartmann,Gerhard M Sessler,Omar Ben Dali,Mario Kupnik

doi:10.3390/polym13213751

Heinz Von Seggern, Sergey Zhukov + Show 4 more

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https://doi.org/10.3390/polym13213751

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Journal: Polymers	Publication Date: Oct 29, 2021
Citations: 11	License type: CC BY 4.0

Affiliation: Technical University of Darmstadt, Merck (Germany)

Abstract

Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N−1) and dynamic (7500 pC N−1) coefficients were achieved. The isothermal stability of the coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic coefficient on seismic mass and acceleration showed high coefficients, even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static coefficients of the suggested structure indicating a potential for further optimization.

Highlights

Charged microporous foams or voided polymer structures, commonly referred to as ferroelectrets or piezoelectrets [1,2], were introduced several decades ago and were reported to show a high longitudinal piezoelectric effect, the magnitude of which was much higher than the response of classical ferroelectric polymers such as PVDF [3,4] and even comparable to the best lead-based piezoceramics such as lead–zirconate–titanate (PZT) [5]
TheInsatnhdiswwicohrkes, aconnewsisstterdatoefgytwfoorftuhnreceti-olanyaelrspegiemzoeenltesctbroethsabnedinwgicshaensdwwaischinetdrobdeutwceede.n The sandwiches consisted of two functional segments both being sandwiched between layers of 25 μm thick fluoroethylene propylene (FEP) films
The thermoplastic polyurethane (TPU) stripes were responsible for the mechanical properties, whereas the air-filled regions were responsible for the piezoelectric properties after corona poling in an electric field exceeding the Paschen breakdown of air

Summary

Introduction

Charged microporous foams or voided polymer structures, commonly referred to as ferroelectrets or piezoelectrets [1,2], were introduced several decades ago and were reported to show a high longitudinal piezoelectric effect, the magnitude of which was much higher than the response of classical ferroelectric polymers such as PVDF [3,4] and even comparable to the best lead-based piezoceramics such as lead–zirconate–titanate (PZT) [5]. Along with other favorable characteristics, including mechanical flexibility, easy processability, good matching to water and, to the human body, as well as relatively low production costs, these materials represent a new type of electroactive polymers [6].

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