Surface ordering in a concentrated suspension of colloidal particles investigated by x-ray scattering methods

The spatial arrangement of colloids near the free surface of a concentrated suspension of colloidal silica in water is investigated by means of x-ray scattering. The weakly charged particles are found to organize in layers along the surface normal direction. The degree of layering decreases with increasing distance from the surface and three layers are identified from the scattering profile. In the lateral direction, the scattering profile indicates a random spatial arrangement of particles at the surface. Based on the findings, a simple structural model for the near surface arrangement of colloidal particles in this system is proposed.