Hyperquenched glassy water and hyperquenched glassy ethanol probed by single molecule spectroscopy.

It is still unclear whether hyperquenched water (i.e., amorphous glassy water) heated to about 140−150 K remains glassy until it crystallizes near 154 K or whether instead it turns into a supercooled and very viscous liquid. It has been proposed that the glass transition temperature (Tg) for water is 165 K and not, as previously thought, 136 K [V. Velikov et al., Science, 294, 2335 (2001)]. Support for both interpretations exists in the literature, since the Tg of water is difficult to measure due to the formation of metastable cubic ice (Ic) near 154 K. To address the nature of water in the 110−160 K temperature range, a confocal microscopy approach is used to study whether single-probe molecules (i.e., Rhodamine 700, Rh-700) embedded in hyperquenched glassy water (HGW) rotate in the temperature range of 110−160 K. If Tg is 136 K and the liquid above this temperature is fragile (or strong with the fragility index m > 7), then rotation of the Rh-700 molecules should be observed several degrees above Tg. I...