We have investigated the stability of TiO2 nanoparticles in media with different
dielectric constants at different pH values. The zeta potential of TiO2 nanoparticle
suspensions was measured by measuring the electrophoretic mobility and hydrodynamic
radius using the dynamic light scattering (DLS) method. We expected a higher stability
of the suspensions with a medium that has a lower dielectric constant. We proved that the
opposite is true, as lowering the dielectric constant of the medium also increases the
electrostatic attraction between the counterions and the nanoparticles. The counterions
accumulate on the surface of the nanoparticles and shield the charge of the nanoparticle,
which is responsible for the repulsive interaction between two nanoparticles. The stability
of the suspensions was higher at a pH further away from the isoelectric point of the
nanoparticles, as the charge of the particles was greater and consequently the repulsion
between them. In this case, the charge shielding has no significant influence on the
stability as in the case of the dielectric constant. We performed five more Monte Carlo
simulations, in each of which we changed the dielectric constant of the medium in the
system. The simulations yielded results that agree with the experimental measurements.
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