Fluorescence Study of Film Formation from PS Latex-TiO2 Composites: Effects of TiO2 Content, Film Thickness and Particle Size

Abstract

Steady-state fluorescence (SSF) technique in conjunction with UV-visible (UVV) technique, atomic force microscope (AFM) and scanning electron microscope (SEM) is used for studying film formation from TiO2 covered polystyrene (PS) latex particles. The effects of TiO2 content, film thickness and PS particle size on film formation and structure properties of PS/TiO2 composites are studied. For this purpose, in the first part, two different sets of PS films with thicknesses of 5 and 20 mu m were prepared from pyrene-(P-) labeled PS particles (320 nm) and covered with various layers of TiO2 with the use of dip-coating method. These films were then annealed at elevated temperatures above glass transition temperature (T-g) of PS in the range of 100-280 degrees C. Fluorescence emission intensity, I-p from P and transmitted light intensity, I-tr were measured after each annealing step to monitor the stages of film formation. The results show that film formation from PS latexes occurs on the top surface of PS/TiO2 composites and thus develop independent from TiO2 content for both film sets. However, the surface morphology of the films was found to vary with both TiO2 content and film thickness. After removal of PS, thin films provide a quite ordered porous structure while thick films show nonporous structure. In the second Part, two film series were prepared from PS particles with diameters of 203 nm (SmPS) and 382 nm (LgPS) covered with different layers of TiO2 and annealed at elevated temperatures. Results reveal that, SmPS/TiO2 films undergo complete film formation independent of the TiO2 content. However, no film formation occurs above a certain TiO2 content in LgPS/TiO2 films. SEM images demonstrate that SmPS/TiO2 films have highly well-ordered microporous structures with increasing TiO2 content after extraction of PS polymer, whereas LgPS/TiO2 composites show no porous structure for high TiO2 content. Our experiments also show that porous TiO2 films with different sizes could successfully be prepared with this technique.