Even though KCl facilitated aggregation, nanoparticles were initially separated further away from each other. We found that the new interactions limited the number of nanoparticles present at the surface, which was not reported before. Using the Langmuir trough, we explain the observed behavior of PSiFe upon compression at the KCl-containing subphase by analyzing the interactions within the system. Significant changes in the assembly of relatively large particles (around 60 to 70 nm) were caused by modulating the interactions within the 5 nm PNIPAM capping layer in the presence of varying concentrations of ions.