Rheology of concentrated bimodal suspensions of nanosilica in PEG

Abstract

In this work, we investigate the linear viscoelastic properties, yielding, and shear-thickening behaviors of highly concentrated bimodal suspension of nanosilica in poly(ethylene glycol) with a molecular weight of 400 g/mol at volume fractions, ϕ, of 0.59 and 0.61 and particle size ratio of δ = 3.4. Studied bimodal suspensions have a negligible depletion attraction, whereas they show the re-entrant behavior. The viscoelastic responses are studied as a function of the large particles fraction with respect to total loaded particles (R). A strong reduction in the normalized elastic modulus, liquidlike behavior (no yield strain and stress), and the lowest viscosities are observed in the bimodal sample with R = 0.6. When the relative volume fraction of small spheres exceeds that of large spheres, the elastic modulus, yield stress, and viscosity of the system increase. It was found that the Mode-Coupling theory and the Herschel–Bulkley model can predict the behavior of studied bimodal suspensions at ϕ = 0.61. Additionally, we have modeled the shear thickening behavior to determine the critical Peclet number for the onset of hydrocluster formation, PeHC. The lowest PeHC and the weakest shear thickening are observed for bimodal suspensions with the re-entrant behavior.