Tuning Polymorphism of Poly(vinylidene fluoride) Thin Films via Capillary Pen 3D Printing

The β-phase crystal structure of poly(vinylidene fluoride) (PVDF) exhibits superior ferroelectric properties relative to other PVDF polymorphs. Therefore, promotion of this phase via processing is an ongoing pursuit in the field of energy storage, especially for polymer-based dielectric capacitors. However, the β-phase is not thermodynamically favored, requiring implementation of non-equilibrium techniques including stretching, electric field poling, ultrafast quenches from the melt, and filler addition. Here, we demonstrate a method to tune β-phase crystal content in PVDF thin films via capillary pen 3D printing. This allows for fabrication of thin-films of highly controllable thickness and geometry through simple modification of print conditions. By balancing flows within the PVDF solution during printing coupled with solvent evaporation kinetics and controlled substrate temperature, β-phase crystal content can be tuned in stable films of 80-500 nm thickness. Thus, capillary pen 3D printing is a simple, one-step method that allows for precise control over polymer microstructure and demonstrates promise as a technique to prepare thin-films used in polymer-based dielectric materials with increased energy capacitance.