Scalable preparation of hollow ZrO2 microspheres through a liquid-liquid phase reunion assisted sol-gel method

Abstract This study demonstrates the use of a liquid-liquid phase reunion (PR) assisted sol-gel method to prepare hollow ZrO2 microspheres. The oil phase of trichloroethylene and isooctanol mixture (TCE/IO), aqueous phase of the ZrO2 precursor sol, and co-solvent phase propylene glycol monomethyl ether (PGME) were mixed and vigorously stirred to form an emulsion with dispersed sub-micron TCE/IO-rich droplets, which do not aggregate and are stable in the long term. This emulsion was further dispersed in pure TCE/IO to form multicore microdroplets, wherein the inner sub-micron droplets grew unstable and coalesced as one (PR), this led to the transformation of the microdroplets from being multicore to single core. The resultant core-shell structure was stable over the duration of the gelation and the aging processes. Subsequently, hollow ZrO2 microspheres with cavities that could be size controlled were obtained by sintering. The method presented in this study is scalable for achieving an increased productivity due to the self-assembly fabrication of the core-shell droplets by using the liquid-liquid PR method.