Thursday, 26 October 2006
OLCC-McClain (Oakley-Lindsay Center)
119

On the nature of water between 130 K and crystallization as probed by single molecule spectroscopy

Nhan C. Dang1, Tonu Reinot2, and Ryszard Jankowiak1. (1) Kansas State University, Manhattan, KS, (2) BioCrystals, LLC, Ames, IA

It has been recently 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)]. Unfortunately, the Tg of water is difficult to measure due to formation of metastable cubic ice (Ic) at T = 154 K. To address the nature of water in the 130-152 K temperature range, a confocal microscopy approach is used to study whether single-probe molecules (i.e. Rhodamine 700) embedded in hyperquenched water rotate in the above temperature range. If Tg is 136 K and the liquid above this temperature is fragile, rotation of the dye molecules should be observed above 136 K. However, single-molecule spectroscopy using confocal microscopy did not reveal any rotation of single-probe molecules above 136 K, thus eliminating “fragile liquid” as a possible description of water between 136 K and crystallization. This finding is in agreement with recent dielectric relaxation studies [A. Minoguchi et al. Phys. Rev. Letters 93, 215703-1 (2004)] and suggests that the substance above 136 K is not a liquid at all.

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