Electric-field-assisted stagnation-swirl-flame synthesis of porous nanostructured titanium-dioxide films

Abstract

Mesoporous nanostructured titanium-dioxide (TiO2) films, with high uniformity and low packing density, are synthesized in a stagnation swirl-flame setup under an applied electric field, with voltage bias on the substrate and the burner grounded. The effects of uniform external electric-field strength and polarity are studied for different substrate temperatures and precursor-loading concentrations. The results manifest considerable differences in film characteristics, for differing electric fields, with more columnar structures and higher porosities produced under low-magnitude substrate voltages up to |±400|V. Interestingly, films have higher packing density at higher magnitude voltages of |±800|V. At low substrate temperatures, the morphology and structure are more prominent owing to less on-substrate sintering of the nanoparticles. At low-magnitude substrate voltages, oppositely-charged particles are attracted to the substrate, increasing their electrophoretic velocity but decreasing their in-flame growth and agglomeration, resulting in smaller particle size. Along with van der Waals forces and induced dipole–dipole interactions, more columnar-structured growth with lower packing density results. At high-magnitude voltages, the particles seem to acquire the same charge polarity as the voltage bias applied, being repelled and residing in the flame longer, thus increasing in-flame agglomeration and particle size. More branched-structured film growth with high packing density develops.