Sogami-Ise Theory

According to old Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and the more accurate Sogami-Ise theory, 16, 17 The agglomeration and the stability of particle dispersions are determined by the sum of the attractive and repulsive forces between the individual particles. And also it suggest that higher ionic strength of the electrolyte solution diminish interparticle repulsion due to the attractive Van der Waals force, which indicates that the above hydrodynamic diameter of the CeO2 nanoparticles dispersed in a water medium is due to the dominant attractive force over the electrostatic repulsive force, resulting in a highly agglomerated particles, in which case the particle surface charge (Zeta potential) have been noticed that 39.91 mV at pH 6.

Similarly, agglomerated particles were appeared in CeO2 nanoparticles dispersed in an ethanol medium but slightly increasing hydrodynamic diameter approximately 250 nm, with decreasing zeta potential (36.54 mV) was measured at pH 6, resulting that an increase in the ionic strength owing to the compression of the electrical double layer decrease their zeta potential, and therefore promote agglomeration.

Under these conditions, the average hydrodynamic size was 620.3 nm is still higher than the primary particle size 2-3 nm and the deliberate zeta potential was -1.39 mV at pH 7, which indicates that increasing ionic strength leads to increasing hydrodynamic diameter. And also it suggests that at the highest investigated pH i.e. larger than 6 gave rise to the most negative zeta potential. These results are well correlated with the previous results. Gilbert et al., 18 who reported micron-sized