This work presents a new process to print piezoelectric polymer-based sensors through additive manufacturing via 3D printing technology. 3D printing has become an efficient method to fabricate devices with complex geometric structures and embedded functionalities. The motivation of this research was to explore a path towards fully 3D printed multifunctional thin and flexible sensing devices. The 3D printed method used was Fused Deposition Modelling (FDM). A fully 3D printed sensor consisting of a (2.54 cm × 2.54 cm) polyvinylidene fluoride (PVdF) film with thicknesses in the range of ~250 to 350 μm was sandwiched between two fast-drying silver paint printed electrodes with thickness ranging from 10 to 50 μm. The arithmetic average roughness, Ra, of a typical printed PVdF profile with and without printed silver electrodes was 12.9 μm and 7.3 μm, respectively. Silver electrodes were printed to facilitate contact poling and to collect charge generated due to piezoelectricity. The average piezoelectric activity of printed unpoled films was 7.13 pC/N. To perform contact poling, PVdF films were immersed in mineral oil and a controlled voltage was applied to electrodes on one side while electrodes on the opposite side were grounded. Piezoelectric activity in the printed PVdF films was obtained by conventional contact poling at elevated temperatures (100, 110, 120 and 130 °C, respectively) with step increased electric fields, which were varied from 0.4 to 14 MV/m with 1 MV/m increments. The extruding process during 3D printing and the subsequent contact poling process enabled the phase transition from the thermal stable α-phase to the piezoelectric active β-phase and the rearranging of the dipole alignments. The efficiency of poling was evaluated through measurement of the average value of the charge generated by six poled PVdF films in response to mechanical input increasing from 0.29 to 1.91 N with 0.27 N increments. The highest average piezoelectric activity obtained was 56.53 pC/N after poling with an applied electric field of 14 MV/m for 240 minutes. The results demonstrate that by increasing the poling voltages and time, a higher piezoelectric activity (about 8x compared to unpoled films) was achieved, indicating improvement of the β-phase content. This study provides a new method for continuous and direct printing of piezoelectric devices from PVdF polymeric filament rods. This technology opens a new path towards fully 3D printed free-form structured functional materials for sensing applications.

Contact-Poling Enhanced, Fully 3D Printed PVdF Pressure Sensors: Towards 3D Printed Functional Materials

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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