hBN and BaTiO3 reinforced PVDF-HFP matrix piezoelectric nanocomposites for flexible energy storage and harvesting applications

This PhD dissertation introduces poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix piezoelectric nanocomposites reinforced with diverse ceramic nanoparticles for flexible energy storage and harvesting applications. A new process route was demonstrated to form boron nitride nanosheets (BNNSs) through the surface modification of hexagonal boron nitride (hBN) nanoparticles (NPs) with vinyltrimethoxysilane (VTS) as a silane coupling agent. PVDF-HFP matrix nanocomposites were produced by solution casting and melt crystallization by reinforcing unmodified hBN NPs and surface modified BNNSs (BNNS-VTSs) by 0-10 wt.% and unmodified barium titanate (BaTiO3; BT) NPs and surface modified BT (BT-VTS) NPs by 0-25 wt.%. Porous 25% BT-VTS/ PVDF-HFP nanocomposites were prepared for the first time using various phase separation methods. Novel sandwich-structured nanocomposites in BN-BT-BN configuration were fabricated by hot-pressing of solid 4% hBN/PVDF-HFP and solid or interconnected porous 25% BT-VTS/PVDF-HFP nanocomposites. All findings indicated that solution casted 4% hBN/PVDF-HFP nanocomposites presented the highest energy storage performance (641 MVm-1 breakdown strength, 23.2 Jcm-3 energy density, 92% energy efficiency) as a flexible dielectric capacitor due to the insulating nanofillers, which exceeds the previously reported BN incorporated PVDF-based nanocomposites. Furthermore, the energy harvesting performance was improved by a 3D porous microstructure. The porous sandwich-structured 4% hBN/25% BT-VTS/PVDF-HFP nanocomposites gave a power density of 22.11 uWcm-3, indicating their potential for use as flexible piezoelectric nanogenerators in self-powered wearable sensors and actuators to supply harvested biomechanical energy or signals for sensing and bio-electric stimulation.