JJAP Conference Proceedings

JJAP Conf. Proc. 2, 011203 (2014) doi:10.7567/JJAPCP.2.011203

Study of self-assembly for mechanochemically-milled saponite nanoparticles

Kazuomi Numata, Kiminori Sato, Koichiro Fujimoto

  1. Department of Environmental Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
  • Received May 06, 2014
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Abstract

The rheological mechanism of long-term self-assembly triggered by H2O molecules was studied for unmilled and mechanochemically-milled saponite nanoparticles by means of thermogravimetry and differential thermal analysis (TG-DTA), dilatometry (DLT), and positronium (Ps) lifetime spectroscopy. For unmilled saponite, the adsorption of H2O molecules due to hydration caused volume expansion arising from an increase in the basal spacing as well as weight gain with a time scale of ~10 h. Ps lifetime spectroscopy revealed two kinds of voids with sizes of ~0.3 and ~0.9 nm for unmilled saponite before hydration. The intensity of the larger void component in the annihilation spectra decreased from ~9 to ~5% with increasing time up to ~100 h and correspondingly the intensity of the smaller void component increased from ~5 to ~9% due to long-term rheological self-assembly. Both the weight gain and volume expansion were largely suppressed for milled saponite, indicating that the adsorption of H2O molecules is reduced. Furthermore, the larger void disappeared and a single void component, corresponding to a void size slightly larger than the original smaller void, was formed for milled saponite. The intensity of this void, created as a result of destruction, decreased with increasing time up to ~100 h.

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