Effects of Polystrene (PS) Molecular Weight and Metal Oxide (TiO2) Content of PS Latex/TiO2 Nanocomposites on Their Film Formation Behavior

Abstract

Our aim for the research described here was to investigate the effects of the molecular weight (Mw) of the polystrene (PS) latex and the nano-metal oxide (TiO2) content of PS latex/TiO2 nanocomposites on their film formation behavior. With the steady-state fluorescence (SSF) and UV-visible (UVV) techniques, the film formation was monitored through a pyrene-based fluorescence probe. Two instruments were utilized to observe the morphological alterations of the composite films: an atomic force microscope (AFM) and a scanning electron microscope (SEM). Prior to the results experiments, the composite films were prepared in two sets consisting of the latex particles with high Mw (HM) or low Mw (LM), and a dip-coating technique was used at room temperature in order to form multiple layers in each film with TiO2. Then these samples were annealed within the range of 100-280 degrees C, above the glass transition temperature (T-g) of PS. Throughout the annealing process, the film formation was monitored stage by stage based on the fluorescence intensity (I-p) emitted from added pyrene and the transmitted light intensity (I-tr) levels. All the measurements resulted in completion of film formation, independent of the Mw of the PS latexes or the TiO2 content. However, while the void closure process was not observed in the LM films, whose packaging structure was much simpler than that of the HM films, it was observed in the HM films. At the end of the process, a porous structure was obtained by extracting the PS polymer using toluene as the solvent. The surface appearance of the sample films varied according to both the different amounts of TiO2 layers in the composite films and the molecular weight of the PS latexes. For the HM films, interconnected porosity was produced at all TiO2 contents, whereas interconnected pores were not observed for more than 5 TiO2 layers contents in the LM samples. Furthermore, the spectroscopic measurements and the SEM/AFM images indicated that the film formation of the PS latexes took place primarily in the PS layers on the top and bottom film surfaces.