Barium titanate (BaTiO3) nanoparticles were dispersed in ethanol–isopropanol mixtures and their rheological behaviors were examined in terms of surfactant concentration (0–5 wt.% of the solids) and volumetric solids loading (\documentclass[12pt]{minimal}
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\begin{document}$$ \phi = 0.10 - 0.35 $$\end{document}) over a shear-rate (\documentclass[12pt]{minimal}
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\begin{document}$${\mathop \gamma \limits^ \cdot }$$\end{document}) range 1 to 1,000 s−1. An oxyethylene-based polymeric surfactant was used to facilitate the nanoparticle dispersion. A pronounced viscosity reduction, >95% when compared to the suspensions without the dispersant, resulted with a surfactant concentration of 4 wt.% at a constant shear rate of 100 s−1. This finding was in parallel with a simultaneous reduction in the mean “floc” size of the suspensions. Shear-thinning flow character resulted over most of the shear-rate range examined, especially for the concentrated suspensions with ϕ ≥ 0.25. The concentrated suspensions were indeed flocculated. This increased instability was partly due to the compression of electrical double layer as the particulate solids became more crowded in the carrier solvents, and also to the increased “effective” solids concentration because of the preferential adsorption of the surfactant molecules on the nanoparticle surface.
