Steady Shear and Dynamic Rheology of Pure and Hybrid Suspensions of Fumed Silica Nanoparticles and Nanocrystalline Cellulose

Nanomaterials such as fumed silica nanoparticles and nanocrystalline cellulose are emerging materials with many practical applications. One important application of these emerging materials is in the thickening and modification of the rheology of liquids. In this work, the rheological behavior of hybrid suspensions composed of fumed silica nanoparticles (T30) and nanocrystalline cellulose (NCC) was investigated to understand the combined effects of particle concentration and nanoparticle interactions on steady shear and viscoelastic properties. Steady shear measurements were conducted over a broad range of T30 concentrations, while oscillatory rheology was performed on selected high-silica formulations (7.06 and 8.1 wt% T30). The suspensions generally exhibited shear-thinning behavior, indicating progressive microstructural breakdown under increasing shear rate. The addition of NCC significantly increased the suspension consistency, suggesting enhanced particle–particle interactions and structural connectivity. Oscillatory measurements revealed elastic-dominated behavior (G′ ≫ G″) across the entire investigated frequency range for the selected formulations. The incorporation of NCC led to a substantial increase in both storage and loss moduli, with a more pronounced enhancement in the elastic response. For example, the storage modulus of 8.1 wt% T30 suspension increased from about 210 Pa to 8000 Pa as the NCC concentration was increased from 0 to 0.5 wt% at 1 rad/s, indicating the formation of a strongly interconnected viscoelastic network. The enhanced rheological behavior in hybrid suspensions is attributed to synergistic interactions between fumed silica aggregates and rod-like NCC particles, which promote network formation and mechanical reinforcement. Gap-dependent measurements showed negligible variation in the measured moduli, confirming the reliability of the rheological data. These findings demonstrate that small additions of NCC can transform fumed silica suspensions into strongly interconnected gel-like viscoelastic networks, which can be leveraged to enhance bulk rheological structuring and thickening of liquid systems.