Advanced X-Ray scattering methods for the study of structure and its evolution in soft materials with fiber symmetry

Abstract

Abstract. Three recently developed evaluation methods for the automated quantitative analysis of Xray scattering data (small-angle (SAXS) and wide-angle (WAXS)) are presented. They are applicable to extensive series of 2D patterns that are recorded in studies of polymer materials with uniaxial symmetry. The experiments comprise time-resolved studies (melting, crystallization, mechanical properties and fatigue) as well as microbeam-scanning for the study of nanostructure gradients. The methods appear suitable to manage the data flood from modern synchrotron radiation setups aiming at the extraction of quantitative information on the structure evolution inside the material.In microbeam-scanning experiments the recorded scattering patterns are smeared. It is proposed to reconstruct desmeared scattering patterns by an X-ray scattering fiber-computer-tomography (XS-FCT). Reconstruction aberrations yield additional structure information. The true structure variation along the fiber radius is established. Compared to general tomography the experiment is faster by a factor of 100, and reconstruction is faster by a factor of 10 4 . In WAXS fiber patterns should first be mapped into reciprocal space before analysis. After having corrected an erroneous tilt-angle equation, automatic tilt-angle tracking and mapping becomes possible. If polymers fail at low strain, the determination of strain and of structural parameters from the scattering patterns require very high accuracy because the observed variations are subtle. Suitable methods are presented both for the high-precision determination of the macroscopic strain, and for the determination of subtle variations of structure parameters.

Studying nanostructure gradients in injection-molded polypropylene/montmorillonite composites by microbeam small-angle x-ray scattering

“…Instead, they represent a superposition of the structure gradient along the path of the microbeam in the sample. Nevertheless, under certain conditions a computed-tomographic method [35, 36, 48, 49] can be utilized that desmears the scattering patterns from such ‘tomo-scans’ mathematically. Necessary assumptions for such ‘mathematical machining’ are, firstly, the presence of fiber symmetry in each volume element (‘voxel’) of the material (the voxel size given by the step-size of the scan) and secondly, the fiber axis must stay nearly parallel to the cylinder axis everywhere.…”