Macroporous morphology of titania films prepared by sol-gel dip-coating method from a system containing poly(ethylene glycol) and poly(vinylpyrrolidone)

Macroporous titania (TiO2) films were prepared by a sol-gel dip coating method from a system containing poly(ethylene glycol) (PEG) and poly(vinylpyrrolidone) (PVP). The thickness of the macroporous films increased with an increase in PVP concentration, but the excess incorporation of PVP suppressed the macroscopic phase separation and enhanced the formation of macroscopic cracks. The porosity and the domain size were simply determined by PEG concentration. Although both PEG and PVP are hydrogen-bonding polymers having proton-accepting ability, preparation of macroporous TiO2 films was unsuccessful in systems containing only PVP as a polymer. Macroporous TiO2 films having interconnected pore structure as thick as 1 mm were successfully prepared by repeating the deposition several times.