The orientation of the crystalline regions in the vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer with molecular ratio 70:30 has been studied by wide-angle X-ray diffraction. This copolymer crystallizes in the fl-phase or form I upon compression moulding. Dumb-bells 90 mm wide by 50 mm long were drawn at 0.25 mm min-1 and 80-85°C to the natural draw ratio of 7; the oriented sheets were void-free, and the crystal phase remained form I. Some samples were then poled at 200 MV m- 1. Strips 0.5 mm wide of both unpoled and poled samples were examined in a two-circle X-ray diffractometer, and all equatorial co scans corrected for absorption of the X-ray beam. Both (200/1 10) and (3 1 0/020) composite reflections then showed six distinct intensity maxima round the draw direction, separated by 60 ° from each other, indicating a high degree of uniplanar-axial orientation within the drawn sheets. Calculation of the structure factors from two crystal models and comparison with the measured intensity ratios round the draw direction by curve-fitting methods showed that most of the polar b axes of the unpoled material are in the sheet plane (bc sheets), and that poling increases the number of these axes taking on positions 60 ° from this plane, in line with similar results in the poly(vinylidene fluoride) homopolymer
Посилання на статтю:
X-ray structural study of oriented vinylidene fluoride/trifluoroethylene copolymers / J. A. Day, E. L. V. Lewis* and G. R. Davies // Polymer. – 1992. – Vol 33. – P. 1571-1578.