Nanoscale flow field induced by Brownian motion of particles trapped at complex interfaces

The floow field induced by the motion of particles trapped at complex interfaces is nontrivial due to the hydrodynamic coupling of 2D interfacial and 3D bulk systems. We have developed a method to measure nanoscale flow fields around interfacially trapped colloidal particles undergoing pure Brownian motion. By this method, we map the flow field generated by particle displacements, which are decomposed into interfacial hydrodynamic multipoles, including thermally induced force monopole and dipole flows, whose forms differ significantly from their bulk fluid counterparts. Analysis of the detailed flow structures provide key insights essential to understanding the interfacial response and the nature of 2D-3D hydrodynamic coupling.