Three-dimensional morphology of PVDF single crystals forming banded spherulites

We have examined the morphology of poly(vinylidene fluoride) (PVDF) single crystals grown from melt and from blends with poly(ethyl acrylate) (PEA), P VDF/PEA = 0.5/99.5 and 30/70 by weight. The single crystals, of relatively higher molecular weight, were grown isothermally in the temperature range w here banded spherulites are formed with sufficient crystallization time. Th e crystals were extracted by dissolving amorphous PEA and PVDF crystals for med on quenching. The three-dimensional morphology of the single crystals w as examined by transmission electron microscopy (bright field, dark held an d diffraction) with a tilting stage. For all cases, the tilting of chains ( similar to 25-27 degrees) to the fold surface has been confirmed. The three -dimensional shape of all the crystals was chair type for the 30/70 blend a nd pure PVDF. In chair crystals, spiral terraces keep the handedness in eac h growth direction. From these evidence, it is proposed that the chair crys tals with consecutive creation of spiral terraces of the same sense are res ponsible for the twisting relationship between crystallites in the radial d irection of the banded spherulites. (C) 2000 Published by Elsevier Science Ltd.