Twice‐Functionalized Montmorillonite Nanosheets for Polymer‐Derived MMT‐SiOC Nanocomposites: Phase Formation and Porosity

In this study, montmorillonite (MMT) nanosheets are purified and exfoliated from a crude clay source and further twice-functionalized with cetritrimethylammonium bromide and [3-(2-aminoethylamino)propyl]trimethoxysliane (AEAPTMS) to promote dispersion in the preceramic polymer. Phase profiles and compositions of MMT nanoflakes and MMT-silicon oxycarbide (SiOC) are characterized with X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The microstructures are examined by scanning and transmission electron microscopy. MMT nanoflakes are randomly dispersed in the SiOC matrix with α-quartz forming at the MMT-SiOC interface. Pyrolysis to 1400 °C induced the formation of SiC nanowhiskers that are observed up to 20 µm in length and 200 nm in diameter. After selective etching of SiO₂ domains with HF, pore sizes and specific surface areas of MMT-SiOC are analyzed with nitrogen adsorption. The study provided a new fundamental understanding of MMT-SiOC interactions at different pyrolysis temperatures and also led to composites with specific surface areas reaching 120 m² g^-1 up to 1200 °C pyrolysis, and between 340 and 772 m² g^-1 at 1400 °C pyrolysis and pore size distributions between 2 and 5 nm. The methodology and results presented improve the understanding and viability of 2D nanomaterial-reinforced ceramic composites and MMT as a precursor for nanostructured SiC.