Colloidal Diffusion and Hydrodynamic Interactions near Boundaries

Holographic optical tweezers allow trapping of colloidal spheres in fluid in three dimensions. In-line digital holographic microscopy yields time-resolved information on the three dimensional distribution of material in a sample. Analysis of in-line holographic images of diffusing colloidal spheres provides their three dimensional positions with nanometer resolution. We studied diffusion of colloidal spheres in three dimensions as a function of distance from boundary by analyzing particle trajectories generated by blinking optical tweezers and digital holographic microscopy. From the trajectories we calculated the particle-particle and particle-wall hydrodynamic interactions as a function of distance from the boundary. The results will help in understanding interactions between micron-sized colloidal particles near a boundary.