Connectivity of PS-b-PEO templated spherical pores in titanium oxide films

Abstract

Titania films having relatively uniform spherical pores were successfully fabricated using polystyrene-block-poly(ethylene oxide) (PS_n-b-PEO_m) diblock copolymers. Depending on the molecular weight of PS_n-b-PEO_m, the spherical pores were varied from large mesopores (n = 40 000, m = 53 000; ∼40 nm) to macropores (n = 58 600, m = 71 000; ∼60 nm, n = 100 000, m = 150 000; ∼100 nm) in diameter. It was confirmed that the porous structures were thermally stable with crystallization of the titania frameworks. Interconnectivity between the spherical pores was reliant on the micellar arrangement of hydrophobic PS cores, while the amount of isolated pores was increased in the films prepared using low molecular weight PS_n-b-PEO_m. The presence of such isolated pores was confirmed on the basis of adsorption experiments by using a globular hemoprotein cytochrome c (ca. 3.1 nm). Highly interconnected spherical pores, which were preferentially fabricated using high molecular weight PS_n-b-PEO_m, were quite helpful for smooth diffusion–adsorption of bulky proteins inside the porous films.