Estimation of microstructure of titania particulate dispersion through viscosity measurement

Aggregate structure and its variation with shear rate are investigated using viscosity data of titania (TiO2) dispersion consisting of anatase titania particles of 200 nm in diameter and ethylene glycol. The particle volume fraction ϕ ranges from 0.01 to 0.1 and the viscosity measurement is performed at shear rates 1–201 s− 1. The viscosity data exhibit that the dispersion is shear-thinning and titania particles exist in the form of aggregates in the dispersion. The Krieger–Dougherty equation is used to obtain the intrinsic viscosity which is related with the aggregate structure and size. It is found that the intrinsic viscosity for ϕ ≤ 0.04 is different from that for ϕ ≥ 0.05 where gel-like behavior is observed in sedimentation test. A scaling relation is applied to correlate the intrinsic viscosity at low ϕ with the aggregate structure characterized by fractal dimension df and exponent for shear dependence of aggregate size m. Logarithmic linearity between the intrinsic viscosity and shear rate indicates that the aggregates are rigid and thus m is close to 1/3. Therefore, df is 1.9813. Yield stress as a function of ϕ also provides information on m and df at the shear rate just above yield point. The fractal dimension df from the yield stress data is 1.9818 when m = 1/3, which is nearly equal to 1.9813 from the intrinsic viscosity data.