Nanodielectrics are promising materials that can efficiently store a large amount of electrical energy that aredesirable for many electronic and power devices. Control of polymer–particle interface in nanodielectrics is very critical innot only obtaining the improved quality of dispersion but also in altering the dielectric properties. Various surface modifyingagents with linear (alkyl), aromatic (phenyl) and extended aromatic (naphthyl) chemical nature were employed at the epoxy–nanoTiO$_2$ interface. All the surface-modifying agents were successful in passivating the nanoparticles surface and in obtaining the improved quality of polymer–particle dispersion and improved glass transition temperature comparatively. However, allthe surface modifiers were not successful in obtaining the improved dielectric properties of the nanodielectrics, especiallydielectric breakdown resistance. Only the extended aromatic group at the polymer–particle interface, which is more electronwithdrawing in electronic nature than phenyl and alkyl structures, was successful in improving the dielectric breakdownresistance. Thus, the choice of surface-modifying agent based on its chemical and electronic nature is very important inoptimizing the dielectric properties of nanodielectrics. Naphthyl phosphate-modified nanoTiO$_2$–epoxy composite films of$\sim$90–100 $\mu$m thick at 5 vol% particle concentration yielded higher dielectric breakdown resistance than pure epoxy polymer and thereby resulted in about 90% higher electrical energy storage density than the pure epoxy film.