Hyperquenching strategies for researching the energetics and dynamics of liquids

We describe studies, both laboratory and simulation, that take advantage of the intrinsic slowness of relaxation to arrest liquids in unusually "excited" (high potential energy) states by hyperquenching. After such trapping at high "fictive" temperatures we observe vibrational, structural, and energetic properties as the system evolves at low temperatures, during a controlled annealing procedure. In this manner, events that normally occur during change of temperature may be observed occurring during passage of time, at much lower temperatures. At these low temperatures, the smearing effects of vibrationally excited modes may be greatly reduced. We find that the high fictive temperature states are characterized by short relaxation times (already known) and considerably more intense boson peaks (less well known) [1]. The thermodynamic consequences of the increased populations of these low frequency modes are examined with the help of computer simulation and normal mode calculations on model glassformers. Behavior in the vibrational DOS at constant pressure is strikingly different from that at constant volume. For glassformers that can exhibit liquid-liquid transitions, one can use the cold equilibration approach to determine the fragility of the high temperature phase, and the enthalpy of the liquid-liquid transition [2]. References. 1. C. A. Angell, Yuanzheng Yue, Limin Wang, John R. D. Copley, Steve Borick and Stefano Mossa. J. Phys. Cond. Matt. 15, S1051-S1068 (2003) 2. M. C. Wilding, P. F. McMillan, Polyamorphic transitions in yttria-alumina liquids, J. Non-Cryst. Solids 293, 357 (2001).