Additive manufacturing of high-β phase poly(vinylidene fluoride) via precipitation printing

Additive manufacturing of poly(vinylidene fluoride) (PVDF) as a piezoelectric material gained wide research interests over the past decade. Promoting the most polar β phase of PVDF during or after the printing process is the key focus to enhance its piezoelectricity. In this paper, a novel additive manufacturing technique termed precipitation printing is developed to produce high-β phase PVDF with the advantages of achieving geometry complexity and fabrication scalability, which is based on the different solubility of PVDF in two mutually miscible solvents. Through dispensing the PVDF/N,N-dimethylformamide (DMF) solution into a water bath, PVDF is continuously precipitated to form a solid structure while DMF diffuses into water. The β phase fraction of printed PVDF is improved to 64.2%. By further hot pressing of precipitation printed PVDF to reduce internal porosity, the piezoelectric d31 and d31 coefficients are measured to be 1.95 pC·N^-1 and -6.42 pC·N^-1, respectively. Precipitation printing is also demonstrated to fabricate piezoelectric PVDF energy harvesters, such as a stretching mode strip energy harvester and a heel insole energy harvester. Therefore, precipitation printing provides a new additive manufacturing technique for producing high-β phase PVDF with strong piezoelectric effect, which can be potentially used to produce sensors, energy harvesters and actuators.