Polymerization-induced phase separation in the preparation of macroporous TiO2/SiO2 thin films

Macroporous TiO2/SiO2 (TS) composite thin films deposited on glass substrates were successfully prepared through a versatile template-free sol–gel approach based on the hydrolysis and polycondensation of tetrabutyl titanate and tetraethyl orthosilicate. A theoretic explanation for the formation of porous morphology was discussed in relation to the polymerization-induced phase separation and the concurrent sol–gel transition. The mechanism of phase separation was attributed to the spinodal decomposition. The field emission scanning electron microscope (FESEM) results indicate that the surface morphologies of TS thin films strongly depend on the amount of SiO2 sols (mole fraction) and aging time before spin-coating. A systemic method of long-range pore size tailoring for macroporous TS composite thin film was achieved by adjusting mole ratio of TiO2 to SiO2 and the aging time.