Microscopic structure and dynamics of a dense fluid near a smooth wall-video microscopy of colloidal spheres

The authors measure the instantaneous atomic structure and dynamics of a three dimensional (3D) fluid near crystallization in contact with a smooth wall. The 'atoms' are monodisperse highly charged submicrometre spheres in colloidal suspension in water. The authors simultaneously follow the positions of about 2000 spheres using video microscopy, taking snapshots at intervals close to the collision time of the fluid. They find that the dense fluid is layered in the direction perpendicular to the wall, with at least four distinct layers. They compare the microscopic particle dynamics of the first layer of fluid with those of a two dimensional (2D) layer of spheres at the same density but rigidly confined between two smooth walls, on a time scale at which over 96% of the spheres remain in the first 3D layer. They find dramatic differences in the correlation lengths and times, the defect structure and dynamics, the particle trajectories and the self-diffusion times for the two cases.