The self-diffusion of a single large particle in a fluid is usually described by the classic Stokes–Einstein (SE) hydrodynamic relation. However, there are many fluids where the SE prediction for nanoparticles diffusion fails. These systems include diffusion of nanoparticles in porous media, in entangled and unentangled polymer melts and solutions, and protein diffusion in biological environments. A fundamental understanding of the microscopic parameters that govern nanoparticle diffusion is relevant to a wide range of applications. In this work, we present experimental measurements of the tracer diffusion coefficient of small and large nanoparticles that experience strong attractions with unentangled and entangled polymer melt matrices. For the small nanoparticle system, a crossover from suppressed to enhanced diffusion is observed with increasing polymer molecular weight. We interpret these observations based on our theoretical and simulation insights of the preceding article (paper 1) as a result of a crossover from an effective hydrodynamic core–shell to a nonhydrodynamic vehicle mechanism of transport, with the latter strongly dependent on polymer–nanoparticle desorption time. A general zeroth-order qualitative picture for small sticky nanoparticle diffusion in polymer melts is proposed.

中文翻译：

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粘性纳米颗粒在聚合物熔体中的扩散：从抑制到增强运输的交叉。

通常通过经典的斯托克斯-爱因斯坦（SE）流体力学关系来描述单个大颗粒在流体中的自扩散。但是，在许多流体中，对于纳米粒子扩散的SE预测都失败了。这些系统包括纳米粒子在多孔介质中，在纠缠和非纠缠的聚合物熔体和溶液中的扩散，以及蛋白质在生物环境中的扩散。对控制纳米粒子扩散的微观参数的基本理解与广泛的应用相关。在这项工作中，我们提出了对大小不一的纳米粒子的示踪扩散系数的实验测量，这些粒子在未缠结和缠结的聚合物熔体基质中具有很强的吸引力。对于小纳米粒子系统，随着聚合物分子量的增加，观察到了从抑制扩散到增强扩散的过渡。我们是根据前一篇文章（论文1）的理论和模拟见解来解释这些观察结果的，这是由于有效的流体动力核-壳向非流体动力的运移机制交叉转换的结果，后者强烈依赖于聚合物-纳米粒子的解吸作用时间。提出了一般的零级定性图片，用于在聚合物熔体中的小粘性纳米颗粒扩散。后者在很大程度上取决于聚合物-纳米粒子的解吸时间。提出了一般的零级定性图片，用于在聚合物熔体中的小粘性纳米颗粒扩散。后者在很大程度上取决于聚合物-纳米粒子的解吸时间。提出了一般的零级定性图片，用于在聚合物熔体中的小粘性纳米颗粒扩散。