Enhanced Piezoelectric Properties of Poly(Vinylidenefluoride-Co-Trifluoroethylene)/Carbon-Based Nanomaterial Composite Films for Pressure Sensing Applications

In this study, heat and polarization treatments were applied to poly(vinylidenefluoride-co-trifluoroethylene (PVDF-TrFE) films to improve their crystallinity and piezoelectric effect. Carbon-based nanomaterials (CBNs) of multiple dimensions (i.e., modified zero-dimensional (0D) carbon black (OCB), one-dimensional (1D) modified carbon nanotubes (CNT-COOH) and two-dimensional (2D) graphene oxide (GO)) were added to the copolymer to study the effects of different CBN dimensions on the crystallinity and piezoelectric effect of PVDF-TrFE films. Additionally, amphiphilic polymeric dispersants were added to improve the dispersibility of CBNs; the dispersant was synthesized by the amidation, and imidization reactions of styrene-maleic anhydride copolymer (SMAz) and polyoxyalkylene amine (M1000). Polymer solutions with different ratios of CBN to dispersant (z = 10:1, 5:1, 1:1, 1:5, 1:10) were prepared. The enhanced dispersibility enabled the fluorine atoms in the PVDF-TrFE molecular chain to more efficiently form hydrogen bonds with the -COOH group in the CBN, thereby increasing the content of the beta crystal phase (the origin of the piezoelectric effect) of the film. Therefore, the resulting film exhibited a higher output voltage on the application side and better sensitivity on the sensing element. The addition of CNT-COOH and polymeric dispersants increased the beta-phase content in PVDF-TrFE from 73.6% to 86.4%, which in turn raised the piezoelectric coefficient from 19.8 +/- 1.0 to 26.4 +/- 1.3 pC/N. The composite film-based pressure sensor also exhibited a high degree of sensitivity, which is expected to have commercial potential in the future.