Thompson Helen, Soper Alan K, Ricci Maria Antonietta, Bruni Fabio, Skipper Neal T
ISIS Facility, Rutherford Appleton Laboratory, Didcot, OXON, OX11 0QX, United Kingdom.
J Phys Chem B. 2007 May 24;111(20):5610-20. doi: 10.1021/jp0677905. Epub 2007 May 2.
Neutron diffraction data, in conjunction with isotopic substitution of deuterium (D) for hydrogen (H), have been analyzed to determine the three-dimensional structure of water confined in vycor, an archetypal hydrophilic porous silica glass containing channels or pores of approximately 40 A diameter. The data have been incorporated into a Monte Carlo computer simulation of the confined water system, and the site-site potentials have been iteratively refined in order to produce a model ensemble which is consistent with both the neutron diffraction data and two possible geometries of the vycor pores (cylindrical and spherical). This approach has allowed us to investigate in detail the contributions to the experimentally accessible partial pair correlation functions, and ascertain whether particular features arise from interactions of the water molecules with the substrate surface, or from purely geometrical confinement effects. We observe a significant decrease in the first shell water oxygen-oxygen co-ordination number, and a decrease in the number of hydrogen bonds per water molecule from approximately 3.6 in bulk water to approximately 2.2 in confinement. In addition, we observe a significant shift inward of the second peak in the water oxygen-water oxygen coordination shell. Overall, we therefore find that the structure of the water in vycor is strongly perturbed relative to the bulk.
结合用氘（D）取代氢（H）的同位素替代法，对中子衍射数据进行了分析，以确定限制在Vycor中的水的三维结构。Vycor是一种典型的亲水性多孔石英玻璃，含有直径约为40埃的通道或孔隙。这些数据已被纳入受限水系统的蒙特卡罗计算机模拟中，并且对位点 - 位点势进行了迭代优化，以生成一个与中子衍射数据以及Vycor孔隙的两种可能几何形状（圆柱形和球形）均一致的模型系综。这种方法使我们能够详细研究对实验可获取的部分对关联函数的贡献，并确定特定特征是源于水分子与基底表面的相互作用，还是源于纯粹的几何限制效应。我们观察到第一壳层水的氧 - 氧配位数显著降低，并且每个水分子的氢键数量从体相水中的约3.6个减少到受限状态下的约2.2个。此外，我们观察到水氧 - 水氧配位壳层中第二个峰明显向内移动。因此，总体而言，我们发现Vycor中的水结构相对于体相水受到了强烈扰动。
