Interconnected assembly of ZrO₂@SiO₂ nanoparticles with dimensional selectivity and refractive index tunability

Self-assembled alignment of functional nanoparticles is an important strategy to create complexly architectured nanostructures. While there has been significant progress in nanoparticle self-assembly over the past decade, elaborate control over the assembled structures and long-term structural stability have yet to be fully realized. In this study, we have presented a novel synthetic approach for synchronizing the pre-assembly of primary nanoparticles and their subsequent shell-coating, eventually implementing dimensionally controlled ordering of nanoparticles while securing permanent structural stability. In particular, simply by adjusting the dielectric constant of the dispersion medium and accordingly varying the electrostatic repulsion between particles, the aligned structure of nanoparticles was modulated to have different dimensional orderings (i.e., 1D, 2D, or 3D-like assembly). The obtained results were successfully interpreted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Finally, to demonstrate the practical applicability of aligned structures of nanoparticles, 1D-like structured ZrO₂@SiO₂ was synthesized and incorporated inside a polymeric resin as a filler. By virtue of the tuning of the effective refractive index by varying the relative fractions of the ZrO₂ core and the SiO₂ shell, the optical transparency of filler-incorporating polyethersulfone composite films was retained even including a 3 wt% amount of ZrO₂@SiO₂. Also, due to the facilitated structural interconnectivity between the 1D-chain-like filler and the encompassing polymeric matrix, the thermomechanical properties of the composite films were also greatly improved.