Ion-Size Effect at the Surface of a Silica Hydrosol

Abstract

The author used synchrotron x-ray reflectivity to study the ion-size effect for alkali ions (Na${}^{+}$, K${}^{+}$, Rb${}^{+}$, and Cs${}^{+}$), with densities as high as $4\times 10^{18}-7\times 10^{18}$ m${}^{-2}$, suspended above the surface of a colloidal solution of silica nanoparticles in the field generated by the surface electric-double layer. According to the data, large alkali ions preferentially accumulate at the sol's surface replacing smaller ions, a finding that qualitatively agrees with the dependence of the Kharkats-Ulstrup single-ion electrostatic free energy on the ion's radius.

17 pages, 4 figures

References in corpus (3)

• Compact Layer of Alkali Ions at the Surface of Colloidal Silica
• X-ray study of the electric double layer at the n-hexane/nanocolloidal silica interface
• Crystals of Na+ ions at the surface of a silica hydrosol