Phase Separation in Sodium Silicate Thin Films Prepared by Sol-Gel Method

Abstract

Liquid-liquid phase separation in glassy thin films prepared by a Sol-Gel method has been studied in Na₂O-SiO₂ systems. 18Na₂O-82SiO₂ (mol%) films were coated on SiO₂ substrates using a spin coating method. The effects of the heat treatment, sodium content and thickness of the coatings on the morphology of the phase separation were examined. The distribution of sodium concentration in-depth profiling in the film was measured by X-ray photoelectron spectroscopy (XPS). Although the phase separation was not observed on the surface of the annealed film, it was observed on the surface of the film etched by HF solution. The microstructure of the phase separation was different from that of the bulk glasses with similar composition and was strongly influenced by the Na distribution along the depth of the film. It was noted that the diameter of the droplets prepared by phase separation increased with the thickness of the films.