Globular pattern formation of hierarchical ceria nanoarchitecture



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



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 CeIV complexes to CeO2 nanoparticles in an acidic aqueous solution, and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges, resulting in further pattern formation with opalescence. The hierarchically assembled structures in solutions were CeO2 colloids, viz. primary core clusters (1–3 nm) of crystalline ceria and secondary clusters (20–30 nm) 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-optimisation around the nearby free energy landscape prior to bifurcation.




Communications Chemistry: