Understanding the Influence of Nanoparticle Core Size on the Rheology and Ceramic Yield of Preceramic Polymer-Grafted Nanoparticles: Implications for Thermal Protection Systems and Aerospace Propulsion Components

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Preceramic polymer-grafted nanoparticles (PCP GNPs) offer a promising route for improving the processability and ceramic yield of polymer-derived ceramics by combining the attractive attributes of grafted polymers and inorganic cores. The ability to tune polymer characteristics, core type, and overall size of PCP GNPs provides handles to control the resultant properties (e.g., rheology and conversion to ceramic) and hence adapt these systems to desired applications. Though initial studies have explored the influence of polymer chemistry and particle core type on PCP GNP properties, the effect of nanoparticle core size on rheological and pyrolysis behaviors remains underexplored. In this work, a systematic study was performed to determine the role of core size using silica nanoparticles grafted with a model polycarbosilane under identical synthesis conditions. Successful grafting was confirmed by dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). Rheological measurements revealed that smaller cores formed stronger networks resulting in higher storage modulus (factor of ∼1019), higher yield stress (factor of ∼259), and were more shear thinning with higher viscosity (factor of ∼139). TGA studies demonstrated size-dependent increases in char yield, with smaller PCP GNPs achieving the highest mass retention. X-ray diffraction (XRD) analysis confirmed the transition from amorphous silicon oxycarbide (SiOC) to crystalline β-silicon carbide (SiC) at elevated temperatures for all core sizes. The influence of PCP GNP core size on rheological properties suggests that these hybrid systems can be tailored in an application-dependent manner, including extrusion-based additive manufacturing of ceramic components or ceramic matrix composite processing. These findings demonstrate that core-size tuning can support the design of polymer-derived ceramics for demanding aerospace applications, including thermal protection systems and SiC-based parts relevant for propulsion systems.