Neutron diffraction study of cubic ice nucleation in a porous silica network
Neutron diffraction study of cubic ice nucleation in a porous silica network
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多孔二氧化硅网络中立方冰成核的中子衍射研究
DOI：
10.1021/j100237a003
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
C. Wright
中科院分区：
文献类型：
--
作者：
D. Steytler;J. Dore;C. Wright
引言在过去的十年中，相当多的注意力已经提请“异常”的物理性质的水接近亲水界面。1为了在该区域中获得显著比例的水，需要高表面积的载体，并且经常使用可以制备具有特定孔径分布的多孔二氧化硅。各种实验技术2已被应用于多孔二氧化硅中吸收的水，虽然表面效应被普遍承认，但关于它们渗透到液体中的范围的程度仍存在相当大的争议。特别是，关于结构变化得出的结论不一致，可能在某种程度上反映了从结构角度解释动力学性质的模糊性。在以前的中子衍射实验中，我们获得了关于填充在表征良好的二氧化硅Spherisorb S20 W（平均孔径90 μ m）5和Gasil 200（平均孔径20 μ m）的孔隙中的水（D20）的直接结构信息。我们的研究结果表明，在孔隙中的水具有基本上类似的散装液体的结构和任何修改被限制在一个区域内的几个分子层的二氧化硅surfaces.Due毛细管效应的液体的熔点可能会显着降低在微孔二氧化硅6，因此可以用来研究过冷和成核的水在分散状态。在这封信中，最近从这样的实验中获得的数据，显示在Spherisorb在-13 ℃时立方冰Ic的成核。已建立的制备立方冰的方法包括在-140 ℃和-120 ℃之间进行汽相沉积或使应变的高压多晶型物松弛。人们认为立方冰是一种亚稳形式，在超过-120 ℃的温度下迅速恢复为六方冰。因此，我们的结果被认为是独特的，在两个方面，因为他们肯定（a）从液态水立方冰的成核（B）接近环境温度的稳定性可观的程度。
Introduction Over the past decade considerable attention has been drawn to the “anomalous” physical properties of water in close proximity to hydrophilic interfaces. 1 So that sig-nificant proportions of water in this region can be obtained high-surface-area supports are required and porous silicas, which may be prepared with specific pore size distribu-tions, have often been employed. A variety of experimental techniques2 have been applied to water absorbed in porous silicas and, although surface effects are universally ac-knowledged, considerable controversy3 remains concerning the extent of their range of penetration into the liquid. In particular it is likely that inconsistencies in conclusions drawn about structural modifications reflect to some extent the ambiguity involved in interpretation of dynamic properties in terms of structure. In a previous neutron diffraction experiment4 we have obtaineddirect structural information on water (D20) filling the pores of the wellcharacterized silicas Spherisorb S20W (mean pore diam-eter 90Á) 5 and Gasil 200 (mean pore diamter 20 Á). Our results indicate that the water in the pores has a structure essentially similar to that of the bulkliquid and any modification is restricted to a region within a few molecular layers of the silica surface.Due to capillary effects the melting point of liquids may be significantly depressed in microporous silicas6 which therefore can be utilized to investigate supercooling and nucleation of water in a dispersed state. In this Letter, data recently obtained from such an experiment are presented, showing the nucleation of cubic ice Ic in Spherisorb at-13 C. The established methods of pre-paring cubic ice have involved either vapor deposition between-140 and-120 C7 or relaxation of the strained high-pressure polymorphs8 and it is thought to be a metastable form reverting rapidly to hexagonal iceIh at tem-peratures exceeding~-120 C. Our results are therefore considered to be uniquein two respects as they affirm (a) nucleation of cubic ice from liquid water with (b) an appreciable degree of stability close to ambient temperature.