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STRUCTURE-PROPERTY RELATIONSHIPS OF HIERARCHICAL POLYMER MATERIALS

Abstract
Structure-property relationships are central to the analysis and understanding of material systems. The exploration of such relationships for the known material systems and further creating new material systems are essential to solve the existing problems and guide the development of advanced technologies. In this thesis, structure-property relationships at different length scales and material systems are studied. We first study the structure-property relationships of fluid/air interfaces. Capillary interactions occurring at the water/air interface are experimentally quantified with a model containing a superhydrophobic floating object, a liquid marble, and a wall (Chapter 2). The overlapping of interfacial deformations is realized to be crucial for the capillary interactions. We further propose a new explanation of capillary interaction-driven motion of floating objects from the perspective of pressure-induced hydraulic motion of water. Then the structure-property relationships of assembled silica nanoparticles (NPs)/polyimide (PI) composites are explored (Chapter 3). A new fabrication route for integrating assembled silica NP micro-structures into PI is demonstrated. Thermal-mechanical properties of the composite films show the advantageous enhancements of the continuous silica NPs micro-structures for PI. Additionally, the composite films, which provide exposed silica NPs on one surface, were found to be able to be modified post-production to introduce new surface properties. In Chapter 4, we describe the structure-property relationships of a MDA3-NaCl complex, formed from methylenedianiline (MDA) and sodium chloride (NaCl), in polyurethane curing. It can dissociate to release MDA to achieve controllable formation of urea links from amine and isocyanate groups. The curing behavior was found to be heterogeneous and localized, and the size and dispersity of the complex particles are essential for the efficiency and thermo-mechanical properties of the resultant polyurethane elastomers. Finally, structure-property relationships are considered for a silicone coating system. The fracture mechanics of silicone coatings are studied (Chapter 5). Mismatches between thermal expansion coefficients of silicone coatings and silicon substrates were used to introduce thermal strains. The release of the residual elastic strain energy supports the propagation of an initiated crack to form various crack patterns which is influenced by the modulus and thickness of the silicone coating, and the surface property of the coating/substrate interfaces.
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