Structural study of silica particle dispersions by ultra-small-angle x-ray scattering

An ultra-small-angle x-ray-scattering study showed several orders of Bragg diffraction for an aqueous colloidal silica dispersion in a vertically held glass capillary, the first peak being at 150’ ’. The same profile was observed when the capillary was rotated around its axis by (60×m)° (where m is an integer). A different profile was found at (30+60×m)° with the first peak at 85’ ’. This showed that a bcc lattice was maintained with the (110) plane parallel to the capillary wall and with a lattice constant =3000 Å, ${\mathit{d}}_{110}$=2100 Å, and ${\mathit{d}}_{020}$=1500 Å. The closest interparticle distance (2${\mathit{D}}_{\exp }$) was 2600 Å while the average distance from the overall concentration (2${\mathit{D}}_0$) was 2900 Å, indicating the non-space-filling nature of the crystal.