Shear thickening characteristics and mechanism of nano-SiO₂/polyethylene glycol composite system

In order to analyze the influence of nano-solid particles in the thickening process of shear thickening fluid (STF) and its role in the environment of low-speed steady-state shear and high-speed dynamic impact, nano-SiO₂ and polyethylene glycol (PEG 200) were used as the dispersed and continuous phases, and different contents of nano-graphite and nano-diamond particles were used as additives to prepare several STF. The friction coefficient curve and the rheological properties at different temperatures were studied. Based on the critical shear rate, the length of the thickening period and the thickening ratio, the changes of shear thickening mechanism under different temperature environments and different nano-solid additive contents were analyzed. And the mechanical response of the STF under transient high-speed impact conditions was explore through the split Hopkinson pressure bar (SHPB) experiment. The experimental results of rheological properties show that the intermolecular repulsive force is enhanced under high temperature environment, and the formation of molecular clusters requires stronger intermolecular dynamic contact, so the length of the thickening interval is extended. Nano-diamond particles strengthen the contact coupling force and contact probability between the particle clusters, so that the maximum viscosity of the system reaches 1679 Pa·s, the thickening ratio is as high as 318 times, and the rheological properties of the STF are improved. The results of the SHPB experiment show that after being impacted, the STF can complete a dynamic response within a 50-75 μs time range, and the maximum stress can reach 78 MPa. The incident kinetic energy of the bullet is not only transformed into thermal energy and phase change energy of solid-liquid conversion, but also into frictional energy between particles. Therefore, by changing the parameters of the solid additive, the mechanical properties and thickening effect of the STF can be effectively controlled, to prepare the STF suitable for applications in different fields.