Taylor dispersion of finite-sized particles near a boundary*

Brownian objects moving in a shear flow undergo an advection-diffusion coupling typically called Taylor dispersion. Such diffusive objects are normally treated as point-like and the walls are considered as passive reflectors. At nanoscales, however, the size of the dispersed objects and their energetic interactions with the confining boundaries should not be neglected. Through the use of evanescent wave microscopy, we here study the motion of fluorescent nanoparticles in linear shear flow near a plane boundary. By varying the concentration of electrolyte, we show how the electrostatic and hydrodynamic interaction between the particles and the surface affects the dispersion. In particular by varying the salt concentration, we measure a large dispersion increase when the electrostatic repulsion decreases. These results, in agreement with numerical simulations and existing theories, highlight the crucial role of hydrodynamic and energetic particle-surface interactions during Taylor dispersion at nanoscales.