Two-dimensional assemblies of colloidal SiO2 and TiO2 particles prepared by the Langmuir-Blodgett technique

The colloidal particles Of SiO2 and TiO2 were arranged in a two-dimensional assembly on the solid substrate by using the Langmuir-Blodgett technique. The most favorable conditions for yielding uniform and dense packing of particles were examined. From scanning electron microscopy and atomic force microscopy images it was found that the quantity of deposited particles is dependent on the electrostatic interaction between the spreading monolayer and the particles, which could be controlled by changing the surface charge density of the monolayer as well as the pH of the subphase. The distribution of particle size markedly influenced the arrangement of spherical particles. The typical result for SiO2 particles, showing a monoparticle layer with a hexagonal packing arrangement, was obtained when the monodispersed particles with the mean diameter (d) of 110 nm were used at around neutral pH. On the other hand, the TiO2 (d = 45 nm) nanoassembly, revealing the high surface coverage with thin particle layer, was prepared in the pH 5.5-10.7 range at x(ODA) of ca. 0.1. (C) 2001 Academic Press.