Central small-angle diffuse scattering from fibers is made of two components

Small-angle X-ray and neutron scattering from materials with fibrous texture generally includes a central diffuse scattering that is either diamond-shaped or shaped like a two-bladed propeller. The central scattering from fibers of polyacrylonitrile, nylon, and poly(ethylene terephthalate) and in particular the changes seen during deformation and heating have been examined. The result is that all types of central scattering from fibers are best described as having two distinct components, where these components are an extended equatorial streak and an inner nearly isotropic scattering. They arise respectively from objects that do and do not become aligned or elongated during fiber production. Examples of objects that do not become aligned are small spherical voids and solid particles. Objects that do become aligned include internal phase boundaries, and the surfaces of the fibers themselves. The equatorial streak arises from an assembly of such elongated objects preferentially oriented along the fiber axis.