Measuring the Glass Transition in Dense 2D Colloidal Fluids

We use Total Internal Reflection Fluorescence Microscopy (TIRF) to analyze dense colloidal fluids fully restricted to two dimensions near their glass transition. Our experiments use 40-100 nm diameter phospholipid vesicles (nanospheres) produced in the lab and commercially manufactured 500 nm and 1000 nm diameter fluorescent polystyrene spheres (microspheres). The microspheres are individually resolvable under TIRF, which allows us to measure their instantaneous positions in both a fluid and a glass state. For both the nanospheres and the microspheres, the position of the colloidal particles is tracked as a function of time, which allows us to measure the viscosity of the colloidal fluid at a range of particle densities. We are thus able to obtain both structural and dynamical information about two-dimensional dense fluids near their glass transition.