EAGER: Towards molecular scale resolution in studies of the anomalous motion of nanoparticles using liquid phase electron microscopy

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Understanding how small particles move in a fluid near a surface is important for many scientific areas, such as biophysics and colloidal self-assembly. This phenomenon is also relevant to many major emerging technologies, from biomolecular separations to three-dimensional additive manufacturing. For nanometer-sized particles, the ability to capture images of these motions has been extremely limited. Liquid cell transmission electron microscopy is a new technique that has great potential to overcome this limitation, provided it can first be validated with simple model systems. This research project aims to study the motion of nanoparticles near a liquid-solid interface, to classify the type of motion of these particles, and to develop physics-based theoretical models that explain the motion of these particles close to a surface. This knowledge gained from this research project will advance our understanding of how nanoparticles move close to a surface, which presents challenges in many fields including biology, geology, and chemical processing. Through this project a diverse group of undergraduate students will work collaboratively under the guidance of the more senior project participants. These students will learn how to use new data science tools to analyze collected microscopy images and videos.Understanding the motions of nanoparticles in a fluid and close to a surface is of fundamental importance in physics and chemistry. A common method to characterize these motions has been through optical microscopy, which naturally imposes spatial resolution limitations on dynamics. The advent of liquid cell transmission electron microscopy has made it possible to study the nanoscale motion of particles near various surfaces, in the liquid environment, and with high spatial resolution. This research project will investigate the anomalous diffusive motion of a simple and tunable model system of gold nanoparticles in aqueous environments near the silicon nitride membrane of a transmission electron microscope’s liquid cell. Specific aims include i) studying the effect of electron beam dose rate on the anomalous diffusion of gold nanoparticles in in-situ liquid cell transmission electron microscopy. This aim will be accomplished by measuring the trajectories of large numbers of nanoparticles at different electron beam dose rates; ii) exploiting the large scale in-situ microscopy data collected from particle trajectories in time and classifying the type of diffusive motion using deep neural networks; and iii) developing Langevin-based theoretical models to capture the distinctive diffusive characteristics that happen across multiple timescales and to relate the local rheological material properties to the type of motion in the liquid cell environment. If successful, this research would facilitate a new way to study the motion of a nanoparticle close to a surface and thereby advance fundamental understanding of the behavior of matter on the nanometer scale. Such knowledge would also enable the mechanism-guided design of experiments and systems in a wide range of scientific fields including crystallization, biomedical drug delivery, rheology, chemical separations, and additive manufacturing research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.