Over the past century, polymer nanocomposites (PNCs), formed through dispersing nanosized inorganic particles in polymer matrices, have become increasingly important functional and structural materials with various applications in energy, environment, healthcare, and infrastructure. Among the most fundamental aspects of PNCs for industrial purposes are the relationships between PNC processing, the microstructure of the composite material, and the macroscopic properties. However, some aspects of these relationships, including their origins, are still poorly understood and it remains a complex challenge to unravel the fundamental characteristics connecting these relationships. In this dissertation, the aim is to develop new techniques through a combination of small-angle scattering (SAS) and advanced microscopes to develop understandings of how external deformation influences the dispersion state of nanoparticles (NPs) in various industrially relevant processing conditions. Specifically, the target is to show how Scanning Electron Microscopes (SEMs) can be a powerful complimentary technology to aid in the understanding of spatial rearrangement of the NPs in high viscoelastic polymer medium. By breaking down how SEM adds an underutilized manner of inspecting the NP dispersion in direct space for PNCs, and adapting analytical techniques from other disciplines, this work develops a novel methodology with regard to polymers to study how NPs rearrange on the microscopic scale as a result of macroscopic deformation. In order to provide a more complete understanding, both tensile and shear deformation modes have been explored. In tensile deformation, the PNCs have been uniaxially extended to a series of elongation ratios acting as different stages of the NP rearrangement progress for rates well above and below a Weissenberg number, Wi = ı̀ØÏ⁴d = 1, where ı̀Ø is the Hencky strain rate and Ï⁴_d is the polymer's terminal relaxation time. Delaunay Triangulation analysis has been applied to quantify the spacing of the NPs relative to their nearest neighbor, and the results for NP rearrangement have been compared against projections of the macroscopic uniaxial deformation fields believed to hold microscopically for PNCs. This work shows strong deviation from the affine predictions, pointing to important long-missing features in understanding the relationship between the microstructural rearrangement and the macroscopic deformation of PNCs.Complex shear deformation has also been performed through capillary rheometry and the SEM has been used to observe the characteristics of the NP clustering of extruded PNCs. These results show a clear breakdown in the Cox-Merz rule for the flow behaviors of PNCs under capillary extrusion. Moreover, interesting features of microstructural rearrangement of PNCs have been observed, highlighting the strong influence of capillary flow to the final dispersion state of PNCs that also changes with the NP loadings and the applied stress. Given the high relevance of capillary extrusion to advanced manufacturing, the revealed results should have strong implications to future manufacturing of polymer nanocomposites with desired properties.
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