Ice-templated poly(vinylidene fluoride) ferroelectrets

TL;DR

This paper demonstrates a novel, simple, and eco-friendly freeze casting method to produce aligned pore structures in poly(vinylidene fluoride) ferroelectrets, enhancing their piezoelectric properties for sensor and energy harvesting applications.

Contribution

First application of freeze casting to create polymeric ferroelectrets with controlled pore morphology and improved piezoelectric performance.

Findings

Aligned pore channels improve polarization after corona poling.

Porosity volume fractions from 24% to 78% analyzed.

Enhanced piezoelectric charge coefficient (d33) observed.

Abstract

Ferroelectrets are piezoelectrically-active polymer foams that can convert externally applied loads into electric charge. Existing processing routes used to create pores of the desired geometry and degree of alignment appropriate for ferroelectrets are based on complex mechanical stretching and chemical dissolution steps. As a simple, cost effective and environmentally friendly approach, freeze casting is able to produce aligned pores with almost all types of the materials, including polymers. In this work, we present the first demonstration of freeze casting to create polymeric ferroelectrets. The pore morphology, phase analysis, relative permittivity and direct piezoelectric charge coefficient (d33) of porous poly(vinylidene fluoride (PVDF) ferroelectrets with porosity volume fractions ranging from 24% to 78% were analysed. The long-range alignment of pore channels produced during directional freezing was shown to be beneficial in forming a highly polarised structure after breakdown of air in the pore channels via corona poling. This new method opens a way to create tailored pores and voids in ferroelectret materials for transducer applications related to sensors and vibration energy harvesting.