Poly(vinylidene fluoride)/Organic Salt Blends for Improved Optical and Piezoelectricity Performance

Lightweight low-cost solutions to control the focus of light are highly desirable for Augmented Reality (AR) and Virtual Reality (VR) wearables. The piezoelectric polymer poly(vinylidene fluoride) (PVDF) is an attractive candidate for deformable lenses and mirrors with its lightweight, flexible, and transparent properties. However, mechanical stretching of the polymer film is required to increase the piezoelectric performance. Typically, this step cavitates microvoids leading to haze and poor optical quality, unusable for AR/VR applications. This work investigates four different tetrabutylammonium (TBA) organic salts to modify both the PVDF microstructure and stretching process to reduce cavitation and improve optical performance while retaining piezoelectric performance. Among the salts tested, tetrabutylammonium trifluoromethanesulfonate (TBATFSI) was found to be best as a clear additive, reducing cavitation with no impact on piezoelectricity and coloration. By quenching the PVDF films with TBATFSI prior to stretching, films were further improved to reach a haze/per thickness of 0.008 ± 0.001%/μm and a d31 piezoelectricity of 35.8 ± 1.9 pC/N with no change in coloration. This ionic salt additive approach demonstrates a scalable process to reduce cavitation in PVDF, resulting in improved optical and piezoelectric films for use in wearable deformable lenses or mirror applications.