Modulating Nanoparticle-Surface Interactions at Liquid-Solid Interfaces via Ion Screening in Liquid-Phase TEM

Understanding how nanoparticles move near liquid-solid interfaces is central to probing nanoscale transport processes in catalysis, biology, and soft polymers. Here, we uncover the physical mechanisms governing anomalous surface diffusion of PEG-coated gold nanorods (AuNRs) moving near the silicon nitride (SiNₓ) membrane of the liquid cell of liquid-phase transmission electron microscopy (LPTEM). By systematically tuning the ionic composition of the diffusion medium, we show how electrostatic interactions, van der Waals forces, and radiolysis-induced screening shape particle motion across a continuum of subdiffusive behaviors. Statistical analyses and deep learning classification reveal a tunable transition between fractional Brownian motion (FBM) in strongly interacting systems (e.g., H{2}O) and annealed transient time motion (ATTM) in screened or passivated environments (e.g., NaCl and phosphate buffered saline (PBS)). These findings challenge the conventional notion that ionic strength alone governs surface mobility, instead emphasizing the role of the local interaction potential. To further elucidate the time-dependent interfacial dynamics, we develop the first passive nanorheology framework in LPTEM, modeling the surface environment as an effective viscoelastic medium. The resulting complex moduli exhibit evolving transitions from elastic to viscous behavior, with relaxation dynamics that correlate directly with diffusion class and radiolytic ion generation. This integrative approach transforms LPTEM from a static nanoimaging modality into a predictive platform for probing nanoscale transport in chemically evolving interfacial environments.