Investigation of Phase-Separated Polymeric Materials via X-ray Scattering Techniques

Abstract

This dissertation presents a discussion of a variety of polymeric materials and their characterization via ultra-small, small, and wide-angle X-ray scattering methods (USAXS/SAXS/WAXS). Specifically, these experimental techniques are employed to investigate the phase separated morphologies that impart unique properties to each class of materials and allow for their use in advanced applications. It is crucial that the morphologies of polymeric materials are thoroughly characterized so that robust structure-property-processing relationships can be constructed. Chapter 2 of this dissertation discusses the fundamental principles of X-ray scattering, which form the basis for more complex experiments discussed throughout this dissertation. While historical, these foundational concepts of X-ray scattering are critical to highlight, due to instruments become increasingly more accessible and user-friendly. In Chapter 3, the origins of X-ray scattering in ion-containing polymers are discussed as it pertains to their unique hydrophilic/hydrophobic phase separated morphologies. These morphologies are becoming increasingly important to understand as ion-containing polymers increase in their commercial use. Chapter 4 discusses the use of USAXS experiments to understand the droplet size distributions of a filler in a polymer matrix and reveals that the liquid droplets in these composites can uniquely change size depending on their volume fraction in the composite. Chapter 5 discusses the use of SAXS and WAXS experiments to investigate the morphology of proton exchange membranes in hydrogen fuel cells. Ultimately, the results from X-ray scattering experiments provide strong evidence that commercial polymers used to make these membranes can mix at the molecular level to form robust membranes. Chapter 6 presents the application of SAXS and WAXS experiments to probe morphologies of 3D-printed polyimide materials. Using a combination of scattering, microscopy, and computational methods, the differences between two chemical variants could be understood, and the origins of void formation were uncovered. Finally, in the Chapter 7 of this dissertation, a selection of other polymeric systems were studied via X-ray scattering methods. Since most of the work presented in this dissertation was collected on a laboratory scale instrument, these experiments display the capability of benchtop instruments to characterize a range of different materials without the need to access a beamline.