THE GLASS-TRANSITION OF COLLOIDAL POLYSTYRENE MICRONETWORK SPHERES - A DYNAMIC LIGHT-SCATTERING STUDY

The collective dynamics of highly concentrated polystyrene micronetwork spheres of 200 nm diameter as measured by photon correlation spectroscopy (PCS) show a glass transition at phi(g) = 0.64 which is indicated independent of any theory through specific changes in the intensity fluctuation pattern. On the 'liquid' side, the same qualitative features as known for molecular liquids or colloidal suspensions close to the glass transition are found. A two-step decay of the density fluctuations is observed with PCS which can be quantitatively interpreted by mode coupling theory (MCT) with a critical volume fraction phi(c) of 0.64, and the analogon of the time-temperature superposition principle holds. However, above phi(c), the density fluctuations do not decay to a finite plateau indicating the freezing of the alpha-process, but show a remnant decay at long times, leading to a dynamical behaviour that cannot be treated within the idealized MCT.