When an applied shear to a uid results in steep rise in its viscosity, it is referred to as Shear Thickening Fluid (STF). In this study, we investigate rheological response of bimodal against mono-dispersed nano sized silica particles in an STF system. Two sizes of nano-silica particles (50 nm fumed silica and 12 nm colloidal silica) were dispersed in polyethylene glycol in various compositions and were compared with monodispersed STF. Results showed lower critical shear rate for shear

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... g in bimodal nanoparticle containing STF than mono-dispersed STF. Higher viscosities were also observed in di erent compositions of bimodal system. Examination of both STF systems under oscillatory stress condition revealed faster response by the bimodal system. Results also indicated that the storage and loss modulus for the bimodal STF system had low critical angular frequency compared to mono-dispersed STF. Study of relaxation time spectrum diagram for the two STFs showed that relaxation time for mono-dispersed STF was faster than that for bimodal STF system.