Djikaev Y S, Ruckenstein Eli
Department of Chemical and Biological Engineering, SUNY at Buffalo, Buffalo, New York 14260, USA.
J Chem Phys. 2009 Mar 28;130(12):124713. doi: 10.1063/1.3098555.
Water molecules, belonging to the first hydration shell around a hydrophobic particle, form fewer hydrogen bonds than bulk molecules. On the other hand, the former (boundary) bonds may be slightly stronger than the latter. When two hydrophobic particles are sufficiently close to each other, the disruption of water-water hydrogen bonds in their first hydration layers can give rise to an additional contribution to their overall interaction potential. Here we present a probabilistic approach to studying this phenomenon. The proposed method allows one to determine the average number of hydrogen bonds per water molecule in the first hydration shell. Numerical evaluations show that in the interplay between a decrease in the number of boundary bonds per water molecule and the enhancement of such a bond the former effect is clearly predominant. As a result, the disruption of boundary hydrogen bonds, which occurs when the first two hydration shells of two particles overlap, leads to an attractive contribution to the overall particle interaction. This contribution is naturally short range, appearing only when the separation between the two particles becomes smaller than four lengths of a hydrogen bond. It is greater than the overall van der Waals interaction potential of the same hydrophobic particles (with typical Hamaker constants) by at least an order of magnitude.
围绕疏水颗粒的第一层水化层中的水分子形成的氢键比本体分子少。另一方面，前者（边界）键可能比后者略强。当两个疏水颗粒彼此足够接近时，它们第一层水化层中水分子间氢键的破坏会对它们的总相互作用势产生额外贡献。在此，我们提出一种概率方法来研究这一现象。所提出的方法能够确定第一层水化层中每个水分子的平均氢键数。数值评估表明，在每个水分子的边界键数量减少与这种键增强之间的相互作用中，前者的影响明显占主导。结果，当两个颗粒的前两层水化层重叠时发生的边界氢键破坏，会对颗粒的总相互作用产生吸引作用。这种作用自然是短程的，仅在两个颗粒之间的间距小于氢键长度的四倍时出现。它比相同疏水颗粒（具有典型的哈梅克常数）的总范德华相互作用势至少大一个数量级。
