Development of PVDF nanocomposite with single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT) for soft morphing actuator

Abstract

Soft morphing actuators can deliver a range of displacements whilst being flexible and lightweight, making them advantageous over traditional mechanical actuators. Piezoelectric polymer polyvinylidene fluoride (PVDF) is combined with nanofillers to achieve superior soft actuator with the nanocomposite than with solely the polymer. This paper investigates and compares the distinctive effects of 1D nanofillers: single-walled carbon nanotubes (SWCNTs) and boron nitride nanotubes (BNNTs), through the promotion of crystal structures and polar β crystals of PVDF, and consequently its actuation ability. Results showed that 80 µm thick 2 wt.% SWCNT/PVDF clamped at both ends with a 10 mm span achieved a high deflection per applied electric field of 414 µm (V mm−1)−1 and deflection of 570 µm. This was due to a combination of fabrication method, physical geometry, and large surface area of SWCNTs leading to enhanced degree of crystallinity, β crystals, dielectric constant, and conductivity. The increase in both overall crystal formation and targeted β crystals lead to a high total β crystal content of 35%, and the conductivity lead to a low applied electric field of 1.3 V mm−1. BNNT/PVDF was able to undergo electric poling due to its insulating nature. BNNT/PVDF achieved a deflection magnitude per applied electric field of 2.9 µm (V mm−1)−1, due to a much higher electric field (90–150 V mm−1). This corresponded to a deflection magnitude of 260 µm, which was a 520% increase from only stretched BNNT/PVDF samples. Both nanocomposites displayed large scale actuation that is greater than the 70 µm deflection (0.9 µm (V mm−1)−1) observed for pure PVDF of same geometry and setup.