Effect of triblock copolymer non-ionic surfactants on the rheology of 3 mol% yttria stabilised zirconia nanosuspensions

The effect of three different molecular weights of a triblock copolymer nonionic surfactant composed of poly(ethylene oxide) and poly(propylene oxide) have been investigated on the zeta potential, stability and rheology of a commercial nanosuspension of 3 mol% yttria stabilised zirconia (3YSZ). Whilst the surfactants showed some evidence of being adsorbed onto the nanoparticle surfaces, it was in insufficient quantities to achieve complete coverage and measurement of the total organic carbon content suggested that the bulk of the surfactants remained in the liquid medium. As a result, there was only a small effect on the zeta potential. Nevertheless, the stability of the suspension was not affected up to solids contents as high as 54 wt%. Whilst the viscosity of the nanosuspension increased slightly with increasing surfactant concentration due to the presence of the polymer molecules, for the lowest molecular weight surfactant the effect was relatively small. Finally, it was observed that if the ionic strength of the suspension was reduced via the removal of free electrolytes in the suspension by dialysis, the viscosity decreased significantly. The reverse behaviour was also observed when extra NH4Cl electrolyte was added to the nanosuspension.