Confinement and substrate-driven polymorph selection in PVDF thin films

The polar polymorphs of poly(vinylidene fluoride) (PVDF) exhibit ferroelectric properties, making polymorph selection of interest for applications such as dielectric capacitors and piezoelectric devices. Adoption of the polar phases often requires mechanical stretching, electric field poling, ultrafast quenches from the melt, or filler addition. Here, we show that polar phase content in PVDF thin films can be tuned via confined crystallization during blade coating, producing a stable film with controlled thickness (~30 - 900 nm) through simple processing modifications. We map the nanoscale phase distribution using atomic force microscopy-based infrared spectroscopy (AFM-IR), revealing depth-dependent polymorph selection. Substrate-driven polar phase nucleation dominates at the film bottom, while nonpolar phase growth leads at the top surface for films greater than ~100 nm in thickness. We also find that substrate chemistry strongly dictates nucleation density and polymorph stability; certain 2D materials promote dense polar nuclei across sufficiently thin films. These findings demonstrate how confinement and interfacial interactions govern PVDF crystallization and inform strategies to design thin-films and nanocomposites with tuned polymorph selection.