Aqueous suspensions of TiO2 nanoparticles (TNPs) with different inorganic salts and polyethylene glycol were analysed using dynamic light scattering and zeta potential measurement. Solutions of noncomplex mono and divalent inorganic ions were used. These suspensions were used to ascertain ion-specific effects of different inorganic counterions on the aggregation behaviour and size of TNPs. Counter ions of higher valence triggered faster destabilization of the suspension resulting in faster aggregation of particles under similar pH conditions. There were no major differences detected between different monovalent ions. The absolute value of zeta potential for all species approached zero with a higher concentration of salt. Multivalent ions also triggered an inversion of charge causing the zeta potential to become negative, despite the low pH in the suspension. Aqueous suspensions of TNPs, and polyethylene (PEG) were also analysed. They were used to ascertain the influence of a long-chain polymer (PEG) on the stability of given suspensions. Higher concentrations of both PEG with different chain lengths led to faster particle aggregation and a drop in zeta potential. The latter, we suggest, is due to the enlargement of particles during measurement. Suspension of TNPs, PEG, and salt resulted in even faster precipitation of aggregates due to the combination of both destabilizing effects. Monte Carlo computer simulations of rough particle model for suspensions of TNPs and salt confirmed experimental findings of the effect of salt on the stability of TNPs. Salt-free simulations resulted in free particles far apart from one another while the simulations with salt resulted in particles in close proximity, indicating destabilization. There were no differences observed between different concentrations of salt with this model. The lowering of the dielectric constant due to the presence of the PEG did not show in the simulation because of the small concentration of PEG used in the experiments.
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