Shulgin Ivan L, Ruckenstein Eli
Department of Chemical and Biological Engineering, State University of New York at Buffalo, Amherst, New York 14260, USA.
J Phys Chem B. 2006 Oct 26;110(42):21381-5. doi: 10.1021/jp064545c.
Simple computer experiments in which various fractions of hydrogen bonds (H-bonds) in ice are allowed to break are presented in this paper. First, up to six million water molecules were used to build an artificial piece of ordinary hexagonal ice in the form of a cube, a monolayer, a bilayer, a trilayer, and thicker layers. Then, certain percentages of H-bonds were broken, and the obtained structures were examined. It was found that a large percentage of H-bonds must be broken in order to completely fragment the network of ice into clusters. For a cubic piece of ice, which can be considered bulk ordinary ice, this percentage is equal to 61% H-bonds, a figure also predicted as the threshold of the percolation theory for ice. If, as usually assumed, 13-20% of H-bonds are broken during melting (estimates based on the comparison between the heats of melting and sublimation of ice), the H-bond network of ice is not fragmented and the overwhelming majority of water molecules (>99%) belong to a new, distorted but unbroken network. The percentage of broken H-bonds required for full fragmentation of layers increases with the number of layers and reaches the bulk value of ice for 5-8 layers. This value is consistent with the literature observation that films of water thicker than 20-30 A have properties close to those of the bulk structure.
本文展示了简单的计算机实验，其中允许冰中不同比例的氢键断裂。首先，使用多达六百万个水分子构建了一块人工普通六方冰，其形态为立方体、单层、双层、三层及更厚的层状。然后，破坏一定比例的氢键，并对得到的结构进行检查。结果发现，为了将冰的网络完全破碎成簇，必须破坏很大比例的氢键。对于一块可被视为块状普通冰的立方冰，这个比例等于61%的氢键，这个数字也被预测为冰的渗流理论阈值。如果像通常所假设的那样，在融化过程中有13% - 20%的氢键被破坏（基于冰的融化热和升华热的比较估算），冰的氢键网络不会破碎，绝大多数水分子（>99%）属于一个新的、扭曲但未断裂的网络。层完全破碎所需的断裂氢键比例随层数增加而增加，对于5 - 8层达到冰的块状值。这个值与文献观察结果一致，即厚度超过20 - 30埃的水膜具有与块状结构相近的性质。
