Rheological behavior of silica based suspensions for shear thickening applications

This thesis focuses on the fabrication and optimization of shear thickening fluids (STFs) for impact protection applications. STFs were prepared by dispersion of fumed silica nanoparticles (NPs) in a polyethylene glycol (PEG) medium. In order to fully understand the shear thickening behavior, the suspensions were varied in the suspended particle size, surface chemistry, and weight fraction. First, the microstructural characteristics of suspensions were investigated by oscillatory rheological techniques. Cryo-scanning electron microscopy was used to link the rheological observations to the microstructural features of suspensions. Then, the shear thickening behavior of suspensions was explored. No thickening behavior was observed for suspensions with a smaller particle size due to increased surface functional group density. Our results proved that the solvation phenomenon, which is the main mechanism for stability/flocculation of suspension and therefore resultant shear response behavior, is not applicable in all cases. Additionally, at the same particle size, increasing the hydrophobicity of particles reduced the thickening extent and delayed the thickening behavior to higher shear values. It was also found that a critical value of 20 wt. % particle is required in order to observe shear thickening behavior. A deep insight is provided into how hydrocluster formation is the most likely explanation for the shear thickening mechanism among other mechanisms (i.e., contact rheology and order−disorder transition). Considering that developed STFs should be able to operate in various service conditions, the effects of temperature and shear history on the performance of STFs were studied. It was unraveled that surface chemistry greatly affects the temperature-dependent behavior of STFs. The findings of this study have significant implications for understanding the effects of various parameters on shear thickening behavior as well as assisting in tailoring STFs for specific applications.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat