Study of a shear thickening fluid: the dispersions of silica nanoparticles in 1-butyl-3-methylimidazolium tetrafluoroborate

The dispersions was prepared by dispersing hydrophilic silica nanoparticles with an average diameter of 50 nm in 1-butyl-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]), and investigated under the steady shear and oscillatory shear, respectively. Experimental results indicate that all of the dispersions present shear thinning, notable shear thickening, and shear thinning successively with increasing shear rate; the shear thickening behavior is derived from silica nanoparticle clusters and strongly controlled by silica nanoparticle content and temperature. The shear thickening fluid (STF) exhibits reversible property and transient response ability, and the time of transient response is no more than 100 ms. The conductivity of the STF is increased with increasing silica nanoparticle content, and the conductivity of 27 wt% dispersions is even two times as big as that of pure [C₄mim][BF₄]. The dispersions with high solid content dilate and present a phase transition changing from a liquid-like to a solid-like soft material in the shear thickening region. A theoretical model is developed to imitate the mechanism of shear thickening in the dispersions.