Advection-diffusion coupling can enhance particle and solute dispersion by orders of magnitude as compared to pure diffusion, with a steady state being reached for confined flow regions such as a nanopore or blood vessel. Here, by using evanescent wave microscopy, we measure for the first time the full dynamics of Taylor dispersion, highlighting the crucial role of the initial concentration profile. We make time-dependent, nanometrically resolved particle dispersion measurements varying nanoparticle size, velocity gradient, and viscosity in submicrometric near-surface flows. Such resolution permits a measure of the full dynamical approach and crossover into the steady state, revealing a family of master curves. Remarkably, our results show that the dynamics depend sensitively on the initial spatial distribution of the nanoparticles. These observations are in quantitative agreement with existing analytical models and numerical simulations performed herein. We anticipate that our study will be a first step toward observing and modelling more complex situations at the nanoscale, such as target finding and chemical reactions in nanoconfined flows, dynamical adsorption and capture problems, as well as nanoscale drug delivery systems.

中文翻译：

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纳米粒子集合的对流-扩散耦合的时间依赖性

与纯扩散相比，对流-扩散耦合可以将粒子和溶质的分散提高几个数量级，并在纳米孔或血管等受限流动区域达到稳态。在这里，通过使用渐逝波显微镜，我们首次测量了泰勒色散的完整动态，突出了初始浓度分布的关键作用。我们在亚微米近表面流动中对不同的纳米颗粒尺寸、速度梯度和粘度进行时间相关、纳米分辨率的颗粒分散测量。这种分辨率允许测量完全动态方法和过渡到稳定状态，揭示一系列主曲线。值得注意的是，我们的结果表明，动力学敏感地取决于纳米粒子的初始空间分布。这些观察结果与此处执行的现有分析模型和数值模拟在数量上一致。我们预计我们的研究将是在纳米尺度上观察和模拟更复杂情况的第一步，例如纳米限制流中的目标发现和化学反应、动态吸附和捕获问题，以及纳米级药物递送系统。