Stick, Slide, or Bounce: Charge Density Controls Nanoparticle Diffusion

Understanding how charged nanoparticles move and interact within charged polymer networks is important for many biological and medical applications. In our work, we combine coarse-grained molecular dynamics simulations with experimental diffusion studies to explore how nanoparticle size, surface charge density, and concentration influence how far and how fast the particles can move through the network. We introduce a scaling law that relates particle diffusion to concentration and surface charge density, showing how both factors strongly affect nanoparticle motion. Our findings, supported by controlled release experiments, reveal that surface charge density is just as important as concentration in determining particle transport. We also identify three distinct behaviors sticking, sliding, and bouncing based on different conditions. Using a metric called normalized attachment time, we examine how electrostatic forces, physical barriers, and fluid dynamics contribute to these behaviors. These results offer practical insights for designing nanoparticles for targeted drug delivery and other advanced material applications.