Modeling the Glass Transition with a 2D Colloid

The dynamics of molecular solids near the glass transition cannot be readily observed using conventional light microscopy. To overcome this limitation, colloidal systems whose larger dispersed particles are analogous to the molecules of a dense fluid are often used to mimic molecular glasses. Experiments using colloids to investigate the glass transition in two dimensions have generally employed quasi-two-dimensional systems where a thin layer of colloidal particles is sedimented on a solid surface. In this work, we study a fully two-dimensional dense colloidal fluid tuned near the glass transition. The system consists of a two-dimensional supported fluid lipid bilayer with small lipid vesicles adhered to it via biotin-avidin bonds. The supported lipid bilayer is a two-dimensional fluid that allows the bound vesicles to move laterally while they remain constrained in-plane as a monolayer. The density of bound vesicles can be tuned by modifying the density of biotin-avidin bonds. We report measurements of the viscosity of the dense colloid, determined via Stokes-Einstein, as the system approaches the glass transition.