Nanostructured and Porous High Temperature Ceramics Using Block Copolymer Mesophases

Abstract

Nanostructured high-temperature ceramics offer great promise in various applications, because of their excellent thermal stability and mechanical properties. Despite advances in oxide materials, nanostructuring of high temperature non-oxide ceramics such as silicon carbonitrides (SiCN) or silicon carbides (SiC) has remained a major challenge. This dissertation describes a well controlled bottom-up approach to overcome this challenge. Block copolymer mesophases are used to structure direct polymer derived ceramic (PDC) precursors on the nanoscopic scale. Subsequent high temperature treatment enables, for the first time, the preparation of mesoporous ceramic materials stable up to 1500 ?C. By blending with an amphiphilic block copolymer, the PDC precursor is expected to selectively swell the hydrophilic block of the polymer. The hybrid morphology can be controlled by systematically increasing the PDC precursor/ block copolymer ratio or by changing characteristics, like the molecular weight of the block copolymer. In fundamental studies to establish hybrid composition structure correlations it is demonstrated that PUMVS is susceptible to reaction with water leading to replacement of nitrogen by oxygen, which can be circumvented by working under dry conditions. Finally, we combine this block copolymer based approach with micromolding and multi-component colloidal self-assembly to make three-dimensionally interconnected, high temperature ceramic materials structured on eight distinct length scales and integrating catalytic functionality from well-dispersed platinum nanoparticles.