Probing nanoscale interactions at the solid-liquid interface via liquid-phase electron microscopy

纳米物体在液体环境中的相互作用对基于胶体系统、自组装过程、界面扩散运动的各种应用的功能至关重要，例如在储能材料中，也与理解生物学中涉及生命分子机械的过程有关。纳米尺度的真实情况通常远不是对称的，导致势的高度复杂性，因此对支配纳米尺度空间组织的物理规则的基本理解仍然不完整，意外/特殊现象不断被发现。该项目的总体目标是研究纳米粒子在固-液界面上的动态行为。原位液相电子显微镜的最新进展使直接成像纳米粒子在纳米尺度上的运动成为可能。利用这个新的“观察窗”，我们和其他人发现了金纳米颗粒在液体中出人意料的缓慢移动，比根据布朗运动预测的速度慢了三个数量级。对于正确描述固-液界面上的动态相互作用，潜在的机理可能是至关重要的。一种可能的机制是，有序的液层导致了超粘性，从而减缓了纳米颗粒的运动。该研究计划包括以下四个工作包：WP 1：建立纳米粒子运动的液体STEM。拟议的研究将首先建立和优化观察不同类型纳米颗粒在液体中缓慢运动的实验条件。将测试纳米颗粒的规格，并评估电子束密度的影响。WP 2：布朗运动的研究。我们将考察纳米粒子运动的布朗运动特征，在布朗运动中，均方位移MSD与时间成线性比例关系，且随温度和纳米粒子半径的变化符合比例定律。将改变几个参数，并分析平移运动。工作组3：其他运动机制的调查。我们还将测试是否存在其他可能的机制，在这些机制中，运动将被驱动或部分驱动，例如，由粘滑机制或静电阻碍。我们还将研究旋转运动。WP 4：研究长程有序液层。最后，我们将研究从固-液界面延伸出几十纳米的长程有序液层的预期存在，并表现出异常高的粘度。作为替代的实验方法，还将用原子力显微镜检查界面液层。

The interactions between nanometer-sized objects in liquid environments are key to the functioning of a variety of applications based on colloidal systems, self-assembly processes, diffusive motion at interfaces, for example, in energy-storage materials, and are also of relevance for understanding processes in biology involved in the molecular machinery of life. The true situation at the nanoscale is typically far from symmetric, leading to a high complexity of the potentials so that the basic understanding of the physical rules governing spatial organization at the nanoscale is still incomplete and unexpected/special phenomena continue to be discovered. The overall goal of this project is to study dynamic nanoparticle behavior at the solid-liquid interface. Recent advances in in situ liquid-phase electron microscopy made it possible to directly image nanoparticle movement at the nanoscale. Using this new “viewing window”, we and others have discovered an unexpected exceptional slow movement of gold nanoparticles in liquid, three orders of magnitude slower than predicted on the basis of Brownian motion. The underlying mechanism is possibly of key importance for a correct description of dynamic interactions at the solid-liquid interface. One possible mechanism is that an ordered liquid layer leads to super-viscosity thus slowing down the nanoparticle motions. The research plan entails the following four work packages:WP 1: Establish Liquid STEM of nanoparticle movement. The proposed research will start out by establishing and optimizing the experimental conditions for observing slow movement of different types of nanoparticles in liquid. The specifications of the nanoparticles will be tested and the effect of the density of the electron beam will be evaluated. WP 2: Investigation of Brownian motion. The movement of nanoparticles will be examined for the characteristics of Brownian motion in which the mean square displacement MSD scales linear with time and a scaling law applies with the temperature, and the nanoparticle radius. Several parameters will be varied and translational movements will be analyzed. WP 3: Investigation of other mechanisms of motion. We will also test the presence of other possible mechanisms in which the motion will be driven or partly driven, for example, by a stick-and-slip mechanism or electrostatic hindrance. We will also examine rotational movements.WP 4: Study long-range ordered liquid layer. Finally, we will investigate the anticipated presence of a long-range ordered liquid layer extending out several tens of nanometers from the solid-liquid interface, and exhibiting an exceptionally high viscosity. The interface liquid layer will also be examined with atomic force microscopy as alternative experimental method.