Compression of cross-linked poly(vinylidene fluoride-co-trifluoro ethylene) films for facile ferroelectric polarization.
ABSTRACT In this study, we demonstrated a facile route for enhancing the ferroelectric polarization of a chemically cross-linked poly(vinylidene fluoride-co-trifluoro ethylene) (PVDF-TrFE) film. Our method is based on thermally induced cross-linking of a PVDF-TrFE film with a 2,2,4-trimethyl-1,6-hexanediamine (THDA) agent under compression. The remanent polarization (P(r)) of a metal/ferroelectric/metal capacitor containing a cross-linked PVDF-TrFE film increased with pressure up to a certain value, whereas no change in the P(r) value was observed in the absence of THDA. A film cross-linked with 10 wt % THDA with respect to PVDF-TrFE under a pressure of 100 kPa exhibited a P(r) of approximately 5.61 μC/cm(2), which is 1.6 times higher than that in the absence of pressure. The enhanced ferroelectric polarization was attributed to highly ordered 20-nm-thick edge-on crystalline lamellae whose c-axes are aligned parallel to the substrate. The lamellae were effective for ferroelectric switching of the PVDF-TrFE when a cross-linked film was recrystallized under pressure. Furthermore, compression of a PVDF-TrFE film with a topographically prepatterned poly(dimethyl siloxane) mold gave rise to a chemically cross-linked micropattern in which edge-on crystalline lamellae were globally oriented over a very large area.