Department of Chemistry, Ecole Normale Supérieure, UMR ENS-CNRS-UPMC 8640, 24 rue Lhomond, 75005 Paris, France.
J Chem Phys. 2012 Jan 28;136(4):044513. doi: 10.1063/1.3679404.
The reorientation dynamics of water confined within nanoscale, hydrophilic silica pores are investigated using molecular dynamics simulations. The effect of surface hydrogen-bonding and electrostatic interactions are examined by comparing with both a silica pore with no charges (representing hydrophobic confinement) and bulk water. The OH reorientation in water is found to slow significantly in hydrophilic confinement compared to bulk water, and is well-described by a power-law decay extending beyond one nanosecond. In contrast, the dynamics of water in the hydrophobic pore are more modestly affected. A two-state model, commonly used to interpret confined liquid properties, is tested by analysis of the position-dependence of the water dynamics. While the two-state model provides a good fit of the orientational decay, our molecular-level analysis evidences that it relies on an over-simplified picture of water dynamics. In contrast with the two-state model assumptions, the interface dynamics is markedly heterogeneous, especially in the hydrophilic pore and there is no single interfacial state with a common dynamics.
利用分子动力学模拟研究了受限在纳米级亲水性二氧化硅孔内的水的重取向动力学。通过与没有电荷的二氧化硅孔（代表疏水性限制）和体相水进行比较，考察了表面氢键和静电相互作用的影响。与体相水相比，在亲水性限制中，水中的 OH 重取向明显减慢，并且在超过 1 纳秒的时间范围内呈幂律衰减。相比之下，水在疏水性孔中的动力学受到的影响较小。通过分析水动力学的位置依赖性，对常用于解释受限液体性质的两态模型进行了测试。虽然两态模型很好地拟合了取向衰减，但我们的分子水平分析表明，它依赖于对水动力学的过于简化的描述。与两态模型的假设相反，界面动力学明显不均匀，特别是在亲水性孔中，没有具有共同动力学的单一界面状态。
