It is well known that water inside hydrophobic nano-channels diffuses faster than bulk water. Recent theoretical studies have shown that this enhancement depends on the size of the hydrophobic nanochannels. However, experimental evidence of this dependence is lacking. Here, by combining two-dimensional nuclear magnetic resonance diffusion–relaxation ($D$–$T_{2eff}$) spectroscopy in the stray field of a superconducting magnet and molecular dynamics simulations, we analyze the size dependence of water dynamics inside Carbon Nanotubes (CNTs) of different diameters ($1.1$–$6.0$ nm), in the temperature range of $265$–$305$ K. Depending on the CNT diameter, the nanotube water is shown to resolve in two or more tubular components acquiring different self-diffusion coefficients. Most notably, a favorable CNT diameter range ($3.0$–$4.5$ nm) is experimentally verified for the first time, in which water molecule dynamics at the center of the CNTs exhibits distinctly non-Arrhenius behavior, characterized by ultrafast diffusion and extraordinary fragility, a result of significant importance in the efforts to understand water behavior in hydrophobic nanochannels.

中文翻译：

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用二维核磁共振扩散松弛D -T 2eff光谱研究了碳纳米管中水扩散的特殊尺寸和温度依赖性。

众所周知，疏水性纳米通道内部的水比散装水扩散得快。最近的理论研究表明，这种增强取决于疏水性纳米通道的大小。但是，缺乏这种依赖性的实验证据。在这里，通过结合二维核磁共振扩散松弛$d$–${Ť}_{2ËFF}$）在超导磁体的杂散场中的光谱学和分子动力学模拟，我们分析了不同直径的碳纳米管（CNT）内部水动力学的尺寸依赖性（$1.1$–$6.0$ nm），在 $265$–$305$ K.根据CNT的直径，显示出纳米管水会分解为两个或更多的管状组件，从而获得不同的自扩散系数。最值得注意的是，CNT的直径范围合适（$3.0$–$4.5$ nm）首次通过实验验证，其中CNT中心的水分子动力学表现出明显的非阿伦尼乌斯行为，具有超快扩散和非凡的脆弱性，这对于理解疏水性中的水行为具有重要意义。纳米通道。