Phthalate-Free Plasticization of Electrostrictive P(VDF−TrFE−CTFE) for Enhanced Actuation

Abstract

PVDF-based electroactive polymer (EAP) actuators offer large field-induced strains, high compliance, and simple and scalable processing, enabling novel applications in soft robots, wearable devices, and medical devices. This work investigates how blending the poly(vinylidene fluoride−trifluoroethylene−chlorotrifluoroethylene) [P(VDF−TrFE−CTFE)] terpolymer with three phthalate-free plasticizers (butyryl trihexyl citrate (BTHC), 1,2-cyclohexanedicarboxylic acid diisononyl ester (DINCH), and tris(2-ethylhexyl) trimellitate (TOTM)) affects the electromechanical transduction properties. Thin films of plasticizer/terpolymer blends were obtained via stencil printing. Film morphology (SEM), crystallinity (XRD), and mechanical and dielectric properties were investigated at different plasticizer contents, and unimorph actuators were fabricated and characterized to quantify the field-induced transverse strains. The maximum strain increased by 12.5× over the neat terpolymer in TOTM 10 wt % blends, reaching 1% at 33.2 V/μm. The largest tip deflections were achieved with TOTM 5 wt %, giving 246.6 μm at 0.1 Hz and 1.65 mm at resonance (33.7 V/μm). At a fixed field of 18 V/μm, blends with BTHC 15 wt % and TOTM 10 wt % produced 3.8 and 4× strain improvements, while DINCH 5 wt % and TOTM 5 wt % delivered 1.48 and 2.2× higher deflections. DINCH- and TOTM-based actuators withstood at least 60% higher fields than the neat terpolymer, likely due to plasticizer diffusion into the EAP film pores. These results show that the studied plasticizers can enhance transduction in P(VDF−TrFE−CTFE), with further improvements expected by reducing film porosity, establishing optimal annealing processes and plasticizer concentrations.