Preparation and Characterization of Macroporous Silicate Films

A straightforward procedure for engineering porosity in thin silicate films has been demonstrated. Macroporous silicate films were fabricated by doping a silica sol prepared from the acid-catalyzed condensation of tetramethoxysilane with polystyrene latex spheres of diameter ranging from 0.3 to 1 μm. After film formation, the polystyrene spheres are etched out the film using chloroform so that the pores are completely exposed on both top and bottom surfaces of the film. The size and distribution of pores in the film and the extent at which the pores are accessible to species in solution were characterized using atomic force microscopy (AFM) and electrochemical methods. AFM reveals that the pores are uniform in size with dimensions defined by the diameter of the particles. The number density of pores in the silica surface was varied from 10 to 150 pores/100 μm 2 by controlling the concentration of microspheres in the sol. Cyclic voltammetry with probe compounds (ruthenium hexaammine, potassium ferricyanide, ferrocene methanol, and ferrocenylmethyl trimethylammonium ion) shows that the extent of pore penetration is a strong function of the ionic charge of the redox probe and the size of the pores.