Effects of solvents on synthesis of piezoelectric polyvinylidene fluoride trifluoroethylene thin films

Polyvinylidene Fluoride (PVDF) and its co-polymer formulations, such as tri-fluoroethylene (TrFE) have been extensively researched as a thin flexible piezoelectric material for a wide range of applications, and new methods of synthesizing the material are continuously being investigated. Researchers have used various solvents to synthesize the PVDF film, yet the effects of these solvents on the piezoelectric properties have not been systematically investigated. The selection of an optimized solvent for polymer dissolution can affect film properties, which could lead to enhanced device performance for piezoelectric-based microsystems. Herein, several solvents were screened for the dissolution of PVDF-TrFE polymer to investigate the effect of solvents and to determine key properties of the solvents that influence the piezoelectric response, so further enhancements can be made in the future. This study investigated 14 different solvents with varying physicochemical properties. The thin films were characterized via X-ray diffraction and quasi-static piezometer measurements. This paper reports that the piezoelectric coefficient of the thin film was highly dependent on the solvent's dipole moment. Our observation revealed that the solvent with the highest dipole moment that was able to completely dissolve the PVDF-TrFE powder produced the film with the highest piezoelectric coefficient. The spin coated film decreased thickness with increasing spin speed, and the piezoelectric coefficient was not affected by the thickness of the film in the range of 1-5 mu m.