Superlattice epitaxy of vinylidene fluoride/frifluoroethylene copolymer crystals on highly oriented pyrolytic graphite

Vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer crystals were grown from the dilute solution on cleaved (0001) surface of highly oriented pyrolytic graphite (HOPG). Using transmission electron microscopy, the orientational relation between the copolymer crystals and cleaved (0001) surface of HOPG is clarified, as well as the supperlattice matching. Electron diffraction (ED) patterns with 6-fold symmetry were observed for the copolymer crystals with VDF molar contents of 59, 65, and 71%. It suggests that a rectangular array of (20 (1) over bar) plane for the high-temperature phase (HP) of the copolymer crystal faces HOPG(0001) plane, from which the molecular chains tilt by 46.7 degrees. The ED pattern with such 6-fold symmetry is attributed to superposition of diffractions from the HP crystallites with three different orientations on HOPG. Such results suggest that epitaxial growth of HP occurred and it was frozen or stabilized even at room temperature due to epitaxial effect or interaction between copolymer molecules and substrate atoms.