| This dissertation involves development of organic/inorganic hybrids utilizing supercritical carbon dioxide (s0002), wherein at least one component has a characteristic length scale below 10 mum. One of the systems studied is a block copolymer (BC) comprising CO2-philic (polydimethylsiloxane) and metallated (polyferrocenylsilane) (PFS) blocks. The BC dissolves into the CO2-phase and forms soft nanostructures of varying size, shape and complexity depending on the pressure, temperature and time of exposure. The nanostructures were "harvested" upon depressurization and analyzed via transmission electron microscopy. Systems such as these are of particular relevance to the microelectronics sector, and this work is intended to open new avenues to novel materials that can be used therein.; Another composite system focused not on the CO2-rich phase, but the polymer-rich phase and CO2-induced swelling and plasticization. Thin films of functionalized PFS homopolymer, a ceramic precursor, were exposed to S0002 in a high-pressure batch vessel at varying temperatures and pressures and for differing saturation times. Isotropic microcellular polymeric foams were produced similar to that for commodity polymers like poly(methylmethacrylate) and polystyrene (PS). Additionally, judicious parameter selection produced bimodal distributions of pore cells and anisotropic pore cells termed "V-directional" cells from the neat homopolymer.; The final composite system comprised silicate (clay) platelets that serve as hard fillers with either nano- or micro-size scales depending on the platelet dispersion. Various fabrication techniques and formulations were explored and this dissertation describes a mechanism for producing intercalated or exfoliated nanocomposites (NCs) from an immiscible system. Exposure of the immiscible NC to an oxidative environment (i) breaks up polymer chains bridging the edges of the silicate platelets allowing a less obstructed pathway for intercalation and (ii) induces chain scission near the periphery of the platelets to provide chains of reduced molecular weight that have more favorable intercalation capability. scCO2 treatment of an immiscible NC system may be postulated to increase the diffusion of chains into the clay gallery, change interfacial tensions or swell the interlayer spacing to increase the d-spacing, all of which might promote intercalation. However, our results indicate that scCO2 behaves similar to inert environments like vacuum and nitrogen for our particular system comprising PS and organically-modified montmorillonite (OM-MMT). To better understand our system, an analysis of the individual polymer and clay properties and stability were undertaken. Insight was gained on the limited thermal stability of OM-MMT and the extreme alignment of clay platelets after processing. The latter may help in the development of impermeable membranes when the platelets are aligned with their surface normal parallel to the diffusive direction. |
