Long-term stability of silane-passivated zirconia nanoparticles with low surface energy

The performance of zirconia nanoparticles (ZrO2 NPs) is critically dependent on their dispersion and stability. Effective control of NP dispersion is crucial for achieving a high refractive index, transparency, and exceptional mechanical properties in organic-inorganic hybrid films that incorporate ZrO2 NPs. In this study, we compared the crystalline properties and stability of ZrO2 NPs synthesized via two distinct methodologies: solvothermal synthesis using a zirconium isopropoxide isopropanol complex (ZII, Zr(OCH(CH3)2)4·(CH3)2CHOH) and sol-gel synthesis using zirconyl chloride octahydrate (ZC, ZrOCl2·8H2O). Both solutions exhibited precipitation, and the particles showed aggregation behavior. Despite being in a suspended state, the particles synthesized using the ZII precursor (T-ZrO2) exhibited hard-sphere behavior, distinct interparticle boundaries, and a tetragonal crystalline phase. However, the particles produced using the ZC precursor (A-ZrO2) were nearly amorphous without well-defined sizes and morphologies. Further, the hydroxyl end groups of both particle types were exchanged using a silane coupling agent (3-(trimethoxysilyl)propyl methacrylate, TMSPM) via hydrolysis and condensation reactions. The presence of the TMSPM groups on the surface of ZrO2 NPs afforded surface-modified TMSPM-T-ZrO2 with enhanced stability and prevented particle aggregation, thus maintaining the dispersion stability for up to one year under ambient conditions. The low surface energy and stabilization of the TMSPM-T-ZrO2 NPs were influenced by the tetragonal crystalline phase, which was conducive to surface modification using a silane coupling agent.