Characterizing the Viscosity of a Dense Two-Dimensional Colloidal Fluid

Experiments intended to study the colloidal glass transition in two-dimensions often employ quasi-two-dimensional samples, where colloidal particles are several layers thick and the particles are not constrained to move in-plane. This methodology limits observation times and could lead to deviations from the theoretical behavior of a purely two-dimensional system. To avoid these limitations, we have developed an experiment with a true two-dimensional colloidal system in which we measure the viscosity of the colloidal fluid at varying densities near the glass transition.

Our experimental set-up consists of a supported lipid bilayer with fluorescent particles attached to the surface. We use light microscopy to image the Brownian motion of the particles in samples of varying densities. We then use the Stokes-Einstein relation to determine viscosity as a function of particle density for this two-dimensional colloidal system.