Comparison of intensity profile analysis and correlation function methods for studying the lamellar structures of semi-crystalline polymers using small-angle X-ray scattering

Changes in the lamellar structure during heating and cooling of a nylon 6,6 polymer were characterized using synchrotron small-angle x-ray scattering (SAXS). The SAXS data were analyzed using two different methods and the derived structural parameters were compared with each other. The first met hod was the conventional correlation function analysis in real space, and the second method was a direct intensity profile fitting in reciprocal space. Both methods yielded similar values of long period, lamellar thickness and amorphous layer thickness. The thickness of the inter-lamellar amorphous layer was smaller in the intensity analysis than by the correlation analysis. It could be that the crystal-amorphous boundary layer is a part of the crystal thickness in the intensity profile analysis. The linear crystallinity obtained by the two methods was similar, and was higher than the bulk crystallinity indicating the presence of significant amorphous material outside the lamellar stacks. However, coherence length of the lamellar stacks and the integrated intensity can be obtained in the intensity profile analysis and not in the correlation function method.