Generating porosity in metal oxides thin films through introduction of polymer micelles

The generation of porosity in Nb 2 O 5 sol–gel films through introduction of polymer micelles of commercially available copolymer Pluronic PE6800 [poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)] was studied using direct observation of film morphology by Transmission Electron Microscopy and indirect calculations of free volume fraction by optical means. Mesoporous Nb 2 O 5 films were deposited by the sol–gel and spin-coating methods and templated with aqueous solutions of Pluronic PE6800 with concentrations below and above critical micelle concentration determined by the modified dye solubilization method. The influence of the duration of the postdeposition annealing on total pore volumes was investigated by reflectance measurements and consequent calculation of optical properties and free volume fraction by Bruggeman effective medium theory. The possible application of the films in optical sensing of vapors has been demonstrated through reflectance measurements prior to and after acetone vapors exposure.