Effect of interfaces on thermophysical properties and block copolymer self-assembly in polymer thin films
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When materials are tailored for use at the nanoscale, thermophysical properties can deviate from their bulk values, and these phenomena are broadly referred to as nanoconfinement effects. In thin films, one of the critical factors of nanoconfinement effects is interfacial interactions; as the film thickness decreases, the interfacial area to volume ratio increases dramatically, often causing interfacial effects to dominate the properties of the entire film. As polymers continue to be leveraged in nanotechnology, from nanocomposites to lithography, understanding the effects of interfaces is highly desired. While numerous studies have revealed how thermophysical properties, (e.g., glass transition temperature (Tg), self-diffusion coefficient (D), and effective viscosity (η [subscript eff]) change with film thickness, correlations between these parameters are still unclear. Herein, the Tg, D, and η [subscript eff] are measured for a model system of unentangled poly (isobutyl methacrylate) (PiBMA, 16-300 nm thick) supported by SiOx. The non-bulk-like correlation between Tg, D, and η [subscript eff] is successfully explained using a three-layer model. To further investigate the effect of confining interfaces, the Tg and D of PiBMA are studied for four multilayer geometries, where the interfacial interactions are varied from strong to weak. The Tg-D relationship of thin films deviates from bulk behavior, and the magnitude of the deviations depends on the polymer-substrate interactions. A friction analysis reveals that this deviation originates from heterogeneous dynamics near the confining interfaces. Engineering interfaces between polymers and substrates is also crucial for BCP lithography, especially on non-traditional substrates (e.g. flexible or 2D materials). In particular, precise control of the surface energy of the underlying substrate is required to produce lithographically useful structures, such as lamellar domains oriented perpendicular to the substrate. In this study, polydopamine is first exploited as a universal adhesive to enable BCP nanopatterning on a variety of flexible materials. In addition, we developed a potentially scalable graphene nanoribbon fabrication method using wetting-transparency assisted BCP lithography. Lastly, inspired by the wetting transparency phenomenon, possible techniques to control the microdomain orientations of BCPs through thin layers are explored using a model bi-layer substrate made from homopolymers of each block, along with a theoretical model based on van der Waals forces.