Application of a CCD-based X-ray diffractometerto polymer fibre diffraction

Abstract

A new diffractometer has been built incorporating a small-area charge-coupled device (CCD) as the X-ray detector. The diffractometer is suitable for studying uniaxially oriented polymer fibres, and produces high resolution fibre diffraction data considerably faster than is possible using a conventional scintillation counter. The sample and detector are mounted on a 3-circle goniometer, and a fibre pattern is constructed from a series of separate diffraction ‘snapshots’, each centred on a different point in reciprocal space. The advantages of the new system are the ability: (1) to produce an undistorted representation of the fibre diffraction pattern; and (2) to access reflections close to the reciprocal fibre axis which are often missing from normal incidence X-ray fibre diffraction photographs. These features make it particularly useful for studying diffuse scattering from partially ordered materials. The operation of the diffractometer is demonstrated using fibres of polyethylene, polypropylene and a copolymer of 1.4-hydroxybenzoic acid with 2,6-hydroxynaphthoic acid. In the latter case a detailed examination of the shapes of the meridional reflection is possible, demonstrating them to be consistent with predictions from current crystallization theories. The effect of imperfect molecular orientation on the appearance of the fibre diffraction patterns is also discussed.