Surface silanized MWCNTs doped PVDF nanocomposite with self-organized dipoles: an intrinsic study on the dielectric, piezoelectric, ferroelectric, and energy harvesting phenomenology

Abstract

Tailoring the dispersion of nanoparticles (NPs) and simultaneously enhancing the polar β-phase of a PVDF polymer is a pivotal issue for developing a high-performing dielectric, ferroelectric and piezoelectric nanocomposite. Inadequate dispersion of NPs and fabrication methods can hinder polar β-phase formation. This study reports a novel strategy to boost and self-organize the polar β-phase by the coalescing role of surface-functionalized (3-aminopropyl triethoxysilane – APTES) multiwalled carbon nanotubes (MWCNTs) and low-temperature phase-inversion. A comprehensive study was implemented to investigate the consequences of surface silanization of MWCNTs on enhancing the polar β-phase and congruently the dielectric, ferroelectric and piezoelectric properties. Also, the capacitance, electrical conductivity, and leakage current of the nanocomposite were investigated. The incorporation of MWCNTs showed an increment of ∼24% in the β-phase fraction. However, the incorporation of MWCNT-APTES NPs showed ∼103% improvement in the polar β-phase. The boosted electroactive β-phase integrally enhanced the dielectric, ferroelectric and piezoelectric properties. Surface functionalized MWCNTs with APTES moieties have improved the relative permittivity of the prepared nanocomposite up to ∼167%. Furthermore, the dielectric loss decreased, and a 233% increase in capacitance was recorded. The integration of MWCNT-APTES NPs inside the polymer matrix reduced the electrical conductivity and leakage current. The J–E curve obtained for the nanocomposite resembled a typical butterfly loop, indicating that the nanocomposite is ferroelectric. In addition, the produced nanocomposites exhibited a typical butterfly loop, which is similar to the bipolar strain against the electric field (S–E) curves, indicating the piezoelectric nature of the nanocomposite. The PVDF/MWCNTs-APTES nanocomposite showed a much higher piezoelectric response of 464 mV in the amplitude signal. In addition, a phase hysteresis loop of the nanocomposite suggested the ferroelectric nature of the material. The incorporation of MWCNTs and MWCNT-APTES NPs enhanced the remanent polarization and piezoelectric charge constant (d₃₃). For practical application a piezoelectric nanogenerator was fabricated using neat PVDF, PVDF/MWCNTs, and PVDF/MWCNTs-APTES nanocomposite. The PVDF/MWCNTs-APTES nanocomposite with a higher β-phase fraction exhibited a closed-circuit peak voltage of ∼13 V across a 10 MΩ resistor and a power density of ∼456 μW cm⁻² across a 1 KΩ resistor. The current investigation confirms that low temperature and surface silanization both contributed to the enhancement of the electroactive polar β-phase. The improved and organized electroactive β-phase intrinsically improved the overall dielectric, ferroelectric, piezoelectric properties of the PVDF/MWCNTs-APTES nanocomposite. The fabricated device shows an excellent energy harvesting method that can be used for practical application.