A hydrodynamic basis for off-axis Brownian diffusion under intermediate confinements in micro-channels
Journal article, 2021

The mobility of a Brownian particle diffusing in a micro-channel is heterogeneous and spatially dependent on the surrounding hydrodynamic resistance fields. The positional asymmetry of such a diffusing particle leads to anisotropies in the observed diffusive behavior. In this paper, we probe such directionally varying diffusive behavior of a spherical nanoparticle diffusing at a location off-set from the centerline of a square micro-channel in a quiescent fluid. This investigation is carried out over varying degrees of intermediate hydrodynamic confinements. A coupled Langevin-immersed boundary method is used for these assessments. We observe that the co-axial diffusivity may be slightly enhanced during off-axis hindered diffusion when compared with a corresponding centerline diffusive behavior. We attribute this increased particle diffusivity to a reduced co-axial fluid resistance through a hydrodynamic basis derived using steady-state CFD solutions to the corresponding Stokes problem. For co-axial motion, the particle creates a recirculating flow pattern around itself when moving along the centerline, whereas it drags along the fluid in between itself and the wall when in close proximity to the latter. These contrasting flow behaviors are responsible for the unexpected enhancement of the co-axial diffusivity for some off-axis positions under intermediate hydrodynamic confinements.


Immersed boundary method

Micro-channel and mobility

Brownian diffusion

Hindered diffusion

Hydrodynamic resistance


Ananda Subramani Kannan

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

Andreas Mark

Fraunhofer-Chalmers Centre

Dario Maggiolo

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

Gaetano Sardina

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

Srdjan Sasic

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

Henrik Ström

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

International Journal of Multiphase Flow

0301-9322 (ISSN)

Vol. 143 103772

Subject Categories

Geophysical Engineering

Ocean and River Engineering

Fluid Mechanics and Acoustics



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