Piezoelectric Flexible Materials Enabled by Hierarchically Porous Graphite ^†

Piezoelectric materials, mainly ceramics, have extensively been used in sensing and energy harvesting due to their capacity to transform mechanical energy into electrical energy. Piezoelectric composites composed of piezoceramic embedded in an insulator polymer were found to conjugate mechanical flexibility and high electro-mechanical coupling constants [1]. The polarization process may be hampered due to the polymer’s low dielectric constant and the non-continuity of the ceramic [1]. Conductive carbon nanoparticles can counteract dielectric discrepancies, while the low connection between the piezoelectric particles remains unknown. State-of-the-art highly porous 3D networks of carbon have recently been developed and are believed to overcome these setbacks [2]. The purpose of this work is to fabricate an innovative piezoelectric material using a 3D graphite network filled with barium titanate, all impregnated by a biobased polymer.

A barium titanate synthesis was perfected through hydrothermal synthesis (conventional and microwave-assisted) at mild temperatures (200 °C) by studying the effect of different reaction times on the tetragonality of the particles. The evaluation of the structural phase was conducted using X-ray diffraction and Raman spectroscopy, while the morphology was studied using scanning electron microscopy. The barium titanate particles were impregnated into the carbon foam using an optimized water suspension, with and without the assistance of voltage, which is thought to accelerate and facilitate the impregnation flow. A chitosan/zein polymer was used to incorporate the resulting apparatus to provide the flexibility needed in the final device. Built-in electrodes were used to test the electrical output given by this device. Piezoresponse force microscopy (PFM) was used to characterize the piezoelectric response of the particles after impregnation. The relationship between structure and overall piezoelectric output will be discussed.