(543b) Tg and Structural Recovery of 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 polystyrene nanorods using the Mettler Toledo Flash differential scanning calorimeter (DSC). The advantages of the Flash DSC include sufficient sensitivity to measure enthalpy recovery for nanogram samples, as well as extension of the measurements to aging times as short as 0.01 s and to aging temperatures as high as 15 K above nominal T_g since high fictive-temperature glass can be created by the fast cooling rates (1000 K/s). The T_g of polystyrene supported nanorods in 20 nm anodized aluminum oxide (AAO) is slightly elevated (~2 K) when compared to the bulk. On the other hand, the T_g of stacked nanorods without support is depressed by as large as 20 K for 20 nm rods at the slowest cooling rates of 0.1 K/s; whereas, T_g is only depressed 10 K at the highest cooling rates of 1000 K/s. These results differ somewhat from those of thin polystyrene films where no T_g depression was observed at the highest cooling rates. Structural recovery is performed as a function of aging time and temperature, and the evolution of the enthalpy is followed. The results will also be discussed in the context of current controversies in the field.