The normal X-ray fibre pattern of polyacrylonitrile (PAN) consists of just two sharp equatorial peaks (dl ~ 0.53 nm and d2 ~ 0.30 nm), and very diffuse meridional and off-axis scattering. This has been attributed to a hexagonal packing of chains, with no periodicity along the chain axis. In this work, we have investigated the effect of a tensile stress on this fibre pattern. It was found that both dl and d2 decreased with increasing stress, but the ratio d~/d 2 remained constant within experimental error at x/~/1. This indicated that the 'molecular rods' decreased in diameter on application of the stress, but their packing remained essentially hexagonal. The normal meridional scattering from PAN shows a two-component broad peak; when stress was applied, there was no shift in the positions of either component, but there was a transfer of intensity from high to low 20 values. This was also consistent with a slight extension of the rod. By adopting a simple model of extending rods, it was possible to compute an X-ray stress-strain curve and a modulus from the change in the two equatorial peaks
Посилання на статтю:
The variation of the d-spacings with stress in the hexagonal polymorph of polyacrylonitrile / R. A. Allen and I. M. Ward // Polymer. – 1994. – Vol 35. – P. 4035-4040.