This study investigates the rheological properties of shear thickening fluids (STFs) formulated by dispersing silica particles in polyethylene glycol (PEG), with the incorporation of multi-walled carbon nanotubes (MWNTs). The influences of silica particle content, carbon nanotube (CNT) loading, and surface functionalization were systematically examined. Rotational rheometry demonstrated that CNT addition significantly reduced the critical shear rate while enhancing the maximum viscosity of the STF. Systematic analysis demonstrated that MWNT incorporation significantly reduces the critical shear rate and enhances the maximum viscosity of the STF by forming bridging networks that reinforce shear-induced hydro-clusters. Crucially, acid-functionalization was established as a viable technique to improve CNT dispersion and stability, allowing for higher loadings and stronger shear thickening responses necessary for designing lightweight, high-performance protective materials. Field emission scanning electron microscopy analysis provided microstructural evidence, confirming that the enhanced performance arises from the high-aspect-ratio CNTs forming a physical bridging network between the silica particles, which effectively stabilizes and reinforces the shear-induced hydro-clusters. These findings offer crucial design guidelines by defining the optimal concentration window and necessity of surface functionalization to maximize the high-performance potential of lightweight CNT-modified shear thickening fluids. Excessive CNT loading, however, induced agglomeration, leading to a deterioration of shear thickening.

Abstract
1. Introduction
2. Experimental Procedure
    2.1. Materials
    2.2. Preparation of Silica Suspensions
    2.3. Preparation of CNT-Silica Suspensions
    2.4. Characterization
3. Results and Discussion
    3.1. Rheological Behavior of Silica-Based STFs
    3.2. Effect of CNT Incorporation on RheologicalProperties
    3.3. Influence of Acid-Functionalized CNTs
    3.4. Microstructural Analysis of Silica-CNT Systems
4. Conclusion
Acknowledgement
References
Author Information

• Young Sil Lee(Industry-Academic Cooperation Foundation, Kumoh National Institute of Technology, Gumi 39177, Republic of Korea)
• Hyo-bin Nam(Department of Chemical Engineering, Kumoh National Institute of Technology, Gumi 39177, Republic of Korea)
• Kwan Han Yoon(Department of Chemical Engineering, Kumoh National Institute of Technology, Gumi 39177, Republic of Korea) Corresponding author