Scanning X-ray ScatteringStudies of Mechanically Processed Polymers
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- Institutt for fysikk 
Employing raster-scanning small- and wide-angle X-ray scattering (SAXS and WAXS), morphological variations in weakly scattering polymers have been mapped. These techniques inherently yield information on multiple length scales, making it possible to correlate structural changes on the atomic, molecular and mesoscale to changes in the micrometer regime, with the former being defined by the dimensions of the scatterers yielding the scattering signal and the latter by the step length of the scan. Solid-state processed poly(3-hexylthiophene) of two different molecular weights was investigated. A clear dependence of the molecular and mesoscopic structure on molecular weight was found. At low molecular weight the polymer backbone exhibited no significant preferred orientation, while the crystalline domains were of sufficiently narrow size distribution to form periodic structures on the mesoscale. At high molecular weight the polymer crystallites were strongly oriented with respect to the film plane, with the side chains preferentially oriented along the surface normal. The crystallites were shown to be periodically arranged both in-plane and outof- plane, with a shorter periodic repetition out-of-plane than in-plane. The increased order in the high molecular sample was attributed to the existence of tie-molecules that exist for sufficiently high molecular weights, connecting neighbouring crystallites and thus providing a certain rigidity to the structure. Injection-molded isotactic polypropylene (PP), with and without talcreinforcement, was investigated. Maps of cross-sectional cuts taken perpendicular to the flow revealed an unexpected, slightly asymmetric orientation distribution of both talc and PP, which is consistent with a temperature gradient across the channel during molding. We hypothesized that this gradient stemmed from an external temperature gradient in molding fixture. Scattering results from samples prepared at different mold temperatures and shear rates, together with simulations of the molding process, indicated that a more complicated explanation, involving an initernal temperature gradient stemming from asymmetrical flow was the cause of the asymmetry. The asymmetric flow was shown to stem from an asymmetrically positioned inlet to the mold. Heterogeneities in the injection molded samples were also shown to correlate well with variations in the shear rate within the mold during solidification. A method for modelling grazing-incidence small-angle X-ray scattering from highly organized mesoporous 3D structures is presented, combining established crystallography formalism with the Distorted Wave Born Approximation. The method is demonstrated by extracting structural information on pore shape and size, by taking advantage of the extinction of certain reflections by variations in the form factor of the pores.