Influence of H-bonding on the crystalline structures and ferroelectric and piezoelectric properties of novel nanogenerators of the lithium salt of 6-amino hexanoic acid incorporated poly(vinylidene fluoride) composites

Abstract

The lithium salt of 6-amino hexanoic acid (Li–AHA) was melt-mixed with poly(vinylidene fluoride) (PVDF), wherein the Li–AHA concentration was varied between 1–15 wt% with the aim of establishing hydrogen bonding between the NH₂ functionality of Li–AHA and the –CF₂ moieties of PVDF. This was followed by compression-moulding as well as solution-casting to make PVDF/Li–AHA composite thin films. FTIR analysis established interactions between the –CF₂ groups in PVDF with amine functional moieties of Li–AHA. Moreover, FTIR analysis estimated that the solution-cast PVDF/Li–AHA composite of 15 wt% Li–AHA exhibited the highest polar phase fraction of ∼60%. Furthermore, ferroelectric analysis showed that the solution-cast PVDF/Li–AHA composite of 15 wt% Li–AHA exhibited the highest remnant polarization of 0.07 μC cm⁻² (at 50 Hz, 1000 V) from the polarization versus electric field loop. Finally, energy harvester devices were fabricated using compression-moulded and solution-cast PVDF/Li–AHA composite films, in which a maximum output voltage of ∼110 V was obtained in the solution-cast PVDF/Li–AHA composite of 15 wt% Li–AHA. The devices also displayed a maximum power density of 75 μW cm⁻² and 85 μW cm⁻² for those fabricated via compression-moulding and solution-casting, respectively. Three different capacitors were efficiently charged by the tapping of the devices made from solution-cast and compression-moulded composite films of 15 wt% Li–AHA. An interrelationship between processing, structure and properties was successfully established in the PVDF/Li–AHA composites with greatly enhanced piezoelectric properties.