Molecular glasses with high fictive temperatures for energy landscape evaluations

With an interest in obtaining data on laboratory glass samples to compare with simulated glasses produced by molecular dynamics computer simulations, we have explored, using calorimetric techniques, the fictive temperatures that can be obtained using different laboratory quenching methods. We describe some useful analytical methods for characterizing quenched samples and, in the process, demonstrate a modified graphical treatment of DSC data that directly yields the m fragility index ("steepness" index) and permits the assembly of enthalpy relaxation data on different liquids in a fragility plot. Using these methods, we provide evidence for the trapping of high-T_g molecular glasses at fictive temperatures up to 1.16T_g and show that fictive temperatures up to and even beyond the crossover temperature for fragile glass formers should be possible using refined electrospray and fiber-spinning techniques. We discuss the relation of the low-T/T_g enthalpy relaxation, found in all hyperquenched glasses, to topographic features of the energy landscape for glass-forming liquids.