Stretchable piezoelectric elastic composites for sensors and energy generators

The search for a piezoelectric elastomer that generates an electrical signal when pressed and stretched has increased significantly in the last decade as they hold great promise in harvesting energy from human motion and monitoring human activities. Here, the excellent elasticity of polydimethylsiloxane-based elastomers and the piezoelectric properties of lead zirconate titanate (PZT) were combined and, using a thermally activated poling process, elastic piezoelectric composites were obtained. For this, two polydimethylsiloxane (PDMS) matrices with a molar mass of 139 kDa and 692 kDa and PZT fillers with particle sizes of 2 and 20 μm were used. For the same poling conditions, an increase in the piezoelectric response with increasing amount of filler, filler size and molar mass of the polymer matrix was observed. Overall, d33 and d31 values of 2.7–40 pC N−1 and 16–48 pC N−1 were achieved in this work with filler contents ranging from 37–72 vol%. A composite material with a PZT filler content of 38 vol% (20 μm particle size) in a commercially available PDMS with a Mw = 139 kg mol−1 exhibited high flexibility, good elasticity with long-term mechanical stretchability and high longitudinal and transverse piezoelectric coefficients of 3.6 pC N−1 and 30 pC N−1, respectively. The higher transverse piezoelectric constant d*31 can be explained by an additional capacitor effect of the composite film structure. These properties are interesting features for energy conversion from human motion, monitoring human activities, and stretchable electronics. The functionality of the newly developed material is demonstrated in a pressed sensor.