Controlled morphology and crystalline phase of poly(ethylene oxide)-TiO₂ nanohybrids

Poly(ethylene oxide) (PEO)-titania (TiO₂) organic-inorganic hybrid powder having different microstructures was synthesized through a sol-gel process and crystallized by subsequent heat treatments at elevated temperatures. As-precipitated hybrid powder showed two distinct morphologies, one of which is spherical and the other is platelike depending upon aging time. It is presumed that the structural variation was highly related with the formation of hydrogen bonds between a chelating agent (2,4-pentanedione: AcAc) and a polymer component (poly(ethylene oxide): PEO). Also, microspherical particles with nanocrystalline anatase core/rutile shell structure were prepared through heat treatment at 800°C. The mechanism of core/shell structure formation was elucidated by the shrinkage during anatase-to-rutile phase transformation, the difference in thermal expansion coefficient (TEC) of two crystals, and further decomposition of remaining organic components trapped in the core. In addition, the powder with platelike structure showed retardation in anatase-rutile phase transformation kinetics compared to that with spherical structure.