Agapov A, Novikov V N, Kisliuk A, Richert R, Sokolov A P
Department of Chemistry and Joint Institute for Neutron Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
J Chem Phys. 2016 Dec 21;145(23):234507. doi: 10.1063/1.4972008.
A possible role of quantum effects, such as tunneling and zero-point energy, in the structural dynamics of supercooled liquids is studied by dielectric spectroscopy. The presented results demonstrate that the liquids, bulk 3-methyl pentane and confined normal and deuterated water, have low glass transition temperature and unusually low for their class of materials steepness of the temperature dependence of structural relaxation (fragility). Although we do not find any signs of tunneling in the structural relaxation of these liquids, their unusually low fragility can be well described by the influence of the quantum fluctuations. Confined water presents an especially interesting case in comparison to the earlier data on bulk low-density amorphous and vapor deposited water. Confined water exhibits a much weaker isotope effect than bulk water, although the effect is still significant. We show that it can be ascribed to the change of the energy barrier for relaxation due to a decrease in the zero-point energy upon D/H substitution. The observed difference in the behavior of confined and bulk water demonstrates high sensitivity of quantum effects to the barrier heights and structure of water. Moreover, these results demonstrate that extrapolation of confined water properties to the bulk water behavior is questionable.
通过介电谱研究了量子效应（如隧穿和零点能）在过冷液体结构动力学中的可能作用。给出的结果表明，液体（本体3-甲基戊烷以及受限的普通水和重水）具有低玻璃化转变温度，并且对于它们这类材料而言，结构弛豫（脆性）的温度依赖性具有异常低的陡度。尽管我们在这些液体的结构弛豫中未发现任何隧穿迹象，但它们异常低的脆性可以通过量子涨落的影响得到很好的描述。与早期关于本体低密度非晶态水和气相沉积水的数据相比，受限水呈现出一个特别有趣的情况。受限水表现出比本体水弱得多的同位素效应，尽管该效应仍然显著。我们表明，这可归因于由于D/H取代导致零点能降低而引起的弛豫能垒的变化。观察到的受限水和本体水行为的差异表明量子效应对于水的能垒高度和结构具有高敏感性。此外，这些结果表明将受限水的性质外推到本体水行为是值得怀疑的。
