论文标题
二氧化硅上的水纳米膜中的时间无关的延伸表明近地表粘弹性
Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity
论文作者
论文摘要
我们使用单分子跟踪来探测界面水的局部流变学。荧光若丹明分子在二氧化硅表面上跟踪，这是环境相对湿度的函数，该杂志控制了冷凝水纳米膜的厚度。在低湿度下，分子在以结合刚度常数的广泛分布为特征的孤立吸附位点附近表现出约束扩散。随后的化学或物理表面钝化选择性地消除了结合位点。在湿度增加时，分子薄膜凝结，允许若丹明分子的近表面转运。运动是延伸的，异常指数随纳米厚度而增加。分子轨迹在时间上是反相关的，千古的，但也具有瞬时结合和间歇性扩散。统计模型表明，水纳米膜中的这种复杂运动具有分数布朗运动的特征，并连续时间随机行走。这与粘弹性纳米膜内的扩散是一致的，这表明在二氧化硅表面附近的持续分子结构。
We used single-molecule tracking to probe the local rheology of interfacial water. Fluorescent rhodamine molecules were tracked on silica surfaces as a function of ambient relative humidity, which controlled the thickness of condensed water nanofilms. At low humidity, the molecules exhibited confined diffusion in the vicinity of isolated adsorption sites characterized by a broad distribution of binding stiffness constants; subsequent chemical or physical surface passivation selectively eliminated stiffer binding sites. At increased humidity, molecularly thin water films condensed, permitting near-surface transport of rhodamine molecules. Motion was subdiffusive, with an anomalous exponent increasing with the nanofilm thickness. Molecular trajectories were temporally anticorrelated, ergodic, but also featured transient binding and intermittent diffusion. Statistical modeling demonstrated that this complex motion in water nanofilms had the characteristics of fractional Brownian motion combined with a continuous time random walk. This was consistent with diffusion within viscoelastic nanofilms, suggesting persistent molecular structuring in the vicinity of the silica surface.
