Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 208996-6100, USA.
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev Lett. 2018 May 11;120(19):196001. doi: 10.1103/PhysRevLett.120.196001.
Individual water molecules or small clusters of water molecules contained within microporous minerals present an extreme case of confinement where the local structure of hydrogen bond networks are dramatically altered from bulk water. In the zinc silicate hemimorphite, the water molecules form a two-dimensional hydrogen bond network with hydroxyl groups in the crystal framework. Here, we present a combined experimental and theoretical study of the structure and dynamics of water molecules within this network. The water molecules undergo a continuous phase transition in their orientational configuration analogous to a two-dimensional Ising model. The incoherent dynamic structure factor reveals two thermally activated relaxation processes, one on a subpicosecond timescale and another on a 10-100 ps timescale, between 70 and 130 K. The slow process is an in-plane reorientation of the water molecule involving the breaking of hydrogen bonds with a framework that, despite the low temperatures involved, is analogous to rotational diffusion of water molecules in the bulk liquid. The fast process is a localized motion of the water molecule with no apparent analogs among known bulk or confined phases of water.
个体水分子或包含在微孔矿物中的小水分子簇呈现出极端的约束情况，其中氢键网络的局部结构从体相水显著改变。在硅锌矿纤锌矿中，水分子与晶体骨架中的羟基形成二维氢键网络。在这里，我们呈现了对该网络内水分子结构和动力学的组合实验和理论研究。水分子在其取向构型中经历连续的相变，类似于二维伊辛模型。非相干动态结构因子揭示了两个热激活弛豫过程，一个在亚皮秒时间尺度上，另一个在 10-100 ps 时间尺度上，在 70 到 130 K 之间。慢过程是水分子的面内重取向，涉及与骨架的氢键断裂，尽管涉及低温，但类似于体相液体中水分子的旋转扩散。快过程是水分子的局域运动，在已知的体相或约束相的水中没有明显的类似物。
