Fig. 4

Ferroelectric properties of pressed and folded poly(vinylidene fluoride) samples. a Bipolar current–electric field (I–E) and displacement–electric field (P–E) loops of P&F PVDF after seven cycles with different M_w of 180, 534 and 670 kg mol⁻¹. P₁ and P₁′ denote the peaks appeared during the application of electric field. P₂ and P₂′ denote the peaks appeared during the reversal of electric field. b A comparison of bipolar remnant polarization P_r and maximum polarization P_max of P&F films with different M_w, and schematic diagram of polar structure change during charging and discharging processes, where the green blocks represent the crystallites, red lines represent the polymer chains with arrows denoting the dipole moment and the dashed lines highlight the polar structure, which was enhanced and grew larger under electric field