UV-visible assessment of hydrocluster formation and rheological behaviour in bimodal and mono-disperse shear thickening fluids

When an applied shear to a fluid results in a steep rise in its viscosity, it is referred to as shear thickening fluid (STF). This study followed two aims: first, to investigate the hydrocluster formation in STF using a novel technique via UV-visible spectroscopy in bimodal and mono-dispersed systems and second, to study the rheological response of bimodal as against mono-dispersed nano-sized silica particles in an STF system. Two nano-sized silica particles (50-nm fumed silica and 12-nm colloidal silica) were dispersed in polyethylene glycol in various compositions and compared with mono-dispersed STF. Bimodal STF in 30 and 35 wt.% (with different ratios of the two nanoparticles) and mono-disperse in 35, 40 and 45 wt.% of OX50 silica particles were prepared. Results showed a lower critical shear rate for the shear thickening in bimodal STF than that in mono-dispersed STF. Also, bimodal system results in reduced amount of nanoparticle used. Higher viscosities were also observed in different composition of bimodal system.