Globular pattern formation of hierarchical ceria nanoarchitectures

Aoyagi, Noboru   ; Motokawa, Ryuhei   ; Okumura, Masahiko   ; Ueda, Yuki   ; Saito, Takumi*; Nishitsuji, Shotaro*; Taguchi, Tomitsugu*; Yomogida, Takumi   ; Sazaki, Gen*; Ikeda, Atsushi  

Dissipative structures often appear as an unstable counterpart of ordered structures owing to fluctuations that do not form a homogeneous phase. Even a multiphase mixture may simultaneously undergo one chemical reaction near equilibrium and another one that is far from equilibrium. Here, we observed in real-time crystal seed formation and simultaneous nanocrystal aggregation proceeding from tetravalent cerium complexes to ceria nanoparticles in an acidic aqueous solution and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges. The hierarchically assembled structures in solutions were ceria colloids, viz. primary core clusters of crystalline ceria and secondary clusters assembled through surface ions. Such self-assembly is widespread in multi-component complex fluids, paradoxically moderating hierarchical reactions. Stability and instability are not only critical but also complementary for co-optimization around the nearby free energy landscape prior to bifurcation.