Comprehensive Rheological Mapping: Flow, Dynamic, and Thermal of Multi-Walled Carbon Nanotube-Modified PEG/Fumed-Silica Shear-Thickening Fluids

Abstract Shear thickening fluids (STFs) are non-Newtonian materials that exhibit a reversible and substantial increase in viscosity under applied shear stress, enabling their use in advanced protective systems, damping technologies, and smart devices. However, optimizing their rheological performance for real-world applications remains a critical challenge. This study presents a systematic investigation into the effect of multi-walled carbon nanotube (MWCNT) reinforcement at varying weight fractions (0.5, 1.0, and 1.5 wt%) on the rheological behavior of STFs based on polyethylene glycol (PEG) and hydrophilic fumed silica (15 wt%). This work delivers a comprehensive assessment of how CNT loading influences key rheological parameters—shear-dependent viscosity, viscoelastic moduli (G′, G″), and complex viscosity—across varying strain, frequency, and temperature. A multistep fabrication strategy was employed to achieve stable, reproducible nanofluids. The results reveal that increasing CNT content enhances both shear thickening intensity and viscoelastic moduli, with the 1.5 wt% sample exhibiting the highest complex viscosity, critical shear rate, and quasi-solid-like behavior under stress. These findings demonstrate the effectiveness of CNTs in strengthening particle–matrix interactions and improving STF performance for energy-absorbing and adaptive material applications.