Rheology and colloidal structure of aqueous TiO 2 nanoparticle suspensions

Abstract

Rheological behavior and suspension structure of anatase titanium dioxide (TiO 2) nanoparticles dispersed in pure water have been investigated over a range of volumetric solids concentrations ( φ=0.05–0.12) and shear rates ( γ=10 1–10 3 s −1). The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregations in the liquid medium. The suspensions became apparently thixotropic as φ was increased above 0.1. Relative viscosity ( η r) of the suspensions followed an exponential form with φ, i.e., η r=13.47e 35.98 φ, revealing a pronounced increase in the degree of particle interactions as φ increased. Fractal dimension ( D f) was estimated from the suspension yield-stress ( τ y) and φ dependence, and was determined as D f∼1.46–1.78 for the flocculated nanoparticle suspensions. This suggested that the suspension structure was probably dominated by the diffusion-limited cluster–cluster aggregation, due mostly to the strong attractions involved in the interparticle potentials. Maximum solids loading ( φ m) of the suspensions was determined as φ m=0.146. This relatively low value of φ m (compared with the random close packing of monosized particles, φ m∼0.64) partially vindicated the existence of a porous, three-dimensional aggregate network of interconnected nanoparticles in the carrier liquid.