Transport of nano-objects in narrow channels: influence of Brownian diffusion, confinement and particle nature

TL;DR

This study investigates how confinement, Brownian motion, and particle type influence nano-object transport in narrow channels, revealing different velocity regimes and the impact of particle distribution and mechanical properties.

Contribution

It provides experimental insights into the combined effects of confinement, diffusion, and particle nature on nano-object transport in microchannels, highlighting mechanisms affecting velocity regimes.

Findings

Two velocity regimes for solid beads linked to particle distribution homogeneity.

Inhomogeneity during entrance affects particle transport and velocity.

Particle nature influences transition between velocity regimes, likely due to mechanical properties.

Abstract

This paper presents experimental results about transport of dilute suspensions of nano-objects in silicon-glass micrometric and sub-micrometric channels. Two kinds of objects are used: solid, rigid latex beads and spherical capsule-shaped, soft polymersomes. They are tracked using fluorescence microscopy. Three parameters are studied: confinement (ratio between particle diameter and channel depth), Brownian diffusion and particle nature. The aim of this work is to understand how these different parameters affect the transport of suspensions in narrow channels and to understand the different mechanisms at play. Concerning the solid beads we observe the appearance of two regimes, one where the experimental mean velocity is close to the expected one and another where this velocity is lower. This is directly related to a competition between confinement, Brownian diffusion and advection. These two regimes are shown to be linked to the homogeneity of particles distribution in the channel depth, which we experimentally deduce from velocity distributions. This inhomogeneity appears during the entrance process into the sub-micrometric channels, as for hydrodynamic separation or deterministic lateral displacement. Concerning the nature of the particles we observed a shift of transition towards the second regime likely due to the relationships between shear stress and polymersomes mechanical properties which could reduce the inhomogeneity imposed by the geometry of our device.