Orientation and lattice structure of microcrystals of colloidal silica particles in dispersions observed by ultra-small-angle X-ray scattering

By using the ultra-small-angle X-ray scattering technique, the influence of shaking on a single crystal (body-centered-cubic (bcc) lattice) in dilute dispersions of colloidal silica particles was studied in a preliminary manner. After being vigorously shaken, the single crystal was broken into microcrystals while the lattice structure and lattice constant were retained. The scattering profile after shaking always showed a 6-fold symmetry and was not due to single crystals or powder-like. This suggests that the (110) planes (the most densely packed in bcc) of the microcrystals were unexpectedly maintained parallel to, and in contact with, the container (capillary) surface. The preference of the (110) planes over other less densely packed planes contradicts the widely accepted double layer interaction theory and provides a positive support to the largely ignored attractive interaction between charged surface and colloidal particles and between particles.