The hydrodynamic radius was constant with the rising KCl concentration (Table ). experimentally. This was also coherent with a report by Weiss et al., who showed increased hydrodynamic radii of polyoxometalate ions, which are inorganic charged nanoparticles, upon salt addition and by charge increase. Weiss et al. also showed that as a consequence of changes in hydrodynamic radius, the normalized friction coefficient increases upon salt addition and by charge increase. The friction factor of an expansion in the hydrodynamic radius with an increase in charge is called electrostatic friction. This stems from interactions with water molecules and small ions. We analyzed the mobility of the studied PSiFe particles (Table ) in terms of this report. The observed leveling-down (in terms of magnitude) of the mobilities µe suggested that the ionic shell was forming around the particles. This was sufficient to make friction the main factor of PSiFe's motion resistance. Considering the particles at the interface required to involve drag coefficients that were related to forces between the charged boundary phase and the charged particles. Both salt concentrations and zeta-potential (in the case of PSiFe, negative but temperature dependent) could additionally influence and blur the conclusions.