Strong piezoelectric-like electromechanical response from single granular PMMA interface

Energy harvesting devices, namely triboelectric nanogenerators (TENGs) and piezoelectric nanogenerators (PENGs), are rapidly garnering interest. As such, a great deal of research is devoted to developing electromechanically responsive materials, particularly flexible polymers. State-of-the-art materials are typically from toxic fluoropolymers, which need to be avoided due to environmental contamination risks. In this work, we investigate the electromechanical response of a granular-based electromechanical device. Close-packed monolayers comprising polymethyl methacrylate (PMMA) beads with diameters of 0.5 or 3 $\mathrm{\mu }$$\mathrm{\mu }$m are assembled using a solvent-free rubbing method. Subsequently, the ordered monolayers are brought into contact, while a force is cyclically applied in a quasi-static mode and during buzzer testing. The beads enable the production of ultra-thin polymer layers (with a combined thickness of only 3.5 $\mathrm{\mu }$$\mathrm{\mu }$m) with controlled morphology (Set by the bead size), which is highly challenging for other polymers. Our findings show that we achieve a $d_{\text{33}}$$d_{\text{33}}$ value of 19 (in quasi-static mode) and 117 pC/N (buzzer test) for the granular-based PMMA electromechanical device, elucidating the great potential of such beads in mechanical energy harvesting devices, as it matches and outperforms most state-of-the-art polyvinylidene fluoride (PVDF) piezoelectric materials.