Understanding Nanoparticle Diffusion and Exploring Interfacial Nanorheology using Molecular Dynamics Simulations

摘要

Since Einstein's famous publication[1] on Brownian motion, it is well-known that for a spherical particle larger than the solvent molecules, the diffusion of the particle in a low- viscosity medium can be predicted by the Stokes-Einstein (SE) equation: where D is the diffusion constant, is Boltzmann's constant, T is the absolute temperature, is the viscosity of the fluid, and a is the particle's radius. However, the motion of the particle suspended in a complex fluid can be very different due to the viscoelastic property of the complex fluid. Another important remaining unanswered question is whether or not the SE equation is applicable to the diffusion of nanoparticles. For example, Tuteja et al [2] reported that cadmium selenide nanoparticles (hydrodynamic radius of 4.7 nm) diffuse approximately 200 times faster in a polystyrene melt than prediction from the SE equation by using X-ray photon correlation spectroscopy (XPCS). Understanding nanoparticle diffusion is important due to the tremendous applications of nanoparticles and “any study targeting the spatial assembly of nanostructures requires an understanding of the nanoparticle dynamics to delineate the kinetics” [2].