The Glass Transition Behavior and Structural Recovery of 2D Stacked Polystyrene Nanorods

The behavior of glass-forming materials confined at the nanoscale has been of considerable interest over the past two decades with conflicting results sparking debate. Here the focus is on the glass transition and associated structural relaxation kinetics of 20 and 350 nm stacked polystyrene nanorods using the Mettler Toledo Flash differential scanning calorimeter (DSC). The T_g of 20 nm stacked polystyrene nanorods is depressed by 20 K and 10 K at cooling rates of 0.1 and 1000 K/s, respectively, whereas bulk-like behavior is observed for 350 nm stacked polystyrene nanorods. Structural recovery is also performed on 20 and 350 nm stacked polystyrene rods as a function of aging time and temperature, and the evolution of the enthalpy is followed. The structural recovery rate is found to be enhanced in the case of 20 nm stacked polystyrene rods when compared to the 350 nm stacked rods. The effect of spatial dimensionality on T_g and structural recovery is also evaluated; in addition, a relaxation time map is constructed to better understand the glass transition and structural recovery kinetics. The results will also be discussed in the context of current controversies in the field.