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

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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.