A model for the nanodomains in polymer-derived SiCO

The polymer-based synthesis of ceramics such as SiCO (and SiCN) leads to the incorporation of significant amounts of carbon into their molecular structure. A key feature of the nanostructure of these polymer-derived ceramics is the revelation of persistent, 1-5 nm size domains by small-angle X-ray scattering. Here we present a model for these nanodomains, which is consistent with the nuclear magnetic resonance (NMR) data and with the phenomenological properties of SiCO (high resistance to creep and viscoelastic behavior). The model consists of clusters of silica tetrahedra encased within an interdomain wall constituted from mixed bonds of SiCO, and from a network of sp(2) carbon. The model predicts the domain size as a function of the carbon content. These predictions are in reasonable agreement with the measurements of the nanodomains in SiCO synthesized with varying carbon contents (the domain size decreases with higher carbon). Simple maps are developed for easy reading of the domain size and the width of the interdomain boundary in the composition diagrams.