Orthokinetic heteroaggregation with nanoparticles: Effect of particle size ratio on aggregate properties

Three different aggregation methods were employed in this work: the addition of HMW polymer, the addition of silica particles (4.3, 105 and 285 nm diameter) and adjustment of suspension pH to 9. Stable alumina dispersions (310 nm) were flocculated using these three methods and each method was found to aggregate the alumina causing equilibrium between formation and destruction of aggregates. The equilibrium size of the aggregates (from largest to smallest) was found to follow the order: HMW Polymer, MP3040, STZL, STXS (285 nm, 105 nm, 4.3 nm) and pH 9. The use of light scattering simulations showed the effect of a second particle species (silica) on the scattering intensity versus wave vector relationship (I versus Q). It was still feasible to obtain a fractal relationship from the light scattering data, even with the complications arising from a two particle asymmetrical system. The fractal dimension increased slightly (2.04, 2.06, 2.19) with an increase in particle size ratio (0.014, 0.339, 0.92) suggesting stronger particle interactions between particles of similar size. The strength of the aggregates was rated from strongest to weakest: HMW Polymer, 285 nm, 105 nm, 4.3 nm and pH 9. Particle–particle interaction energy calculations showed the strongest interaction potential for the larger silica. The particle–particle interaction energy was found to be weaker the smaller the silica particles become.