How contact-line pinning affects the dynamics of colloidal particles at fluid interfaces

Using digital holographic microscopy, a fast 3D imaging technique, we measure the motion of colloidal particles near a liquid interface. We find that micrometer-sized polymer particles take a surprisingly long time -- weeks or even months -- to relax to equilibrium. This behavior can be understood in terms of a dynamic wetting mechanism involving thermally-activated hopping of the contact line over surface defects. I will present results that probe the nature of the pinning sites and how they can affect the pathway to equilibrium.