Single-file escape of colloidal particles from microfluidic channels

TL;DR

This study investigates how colloidal particles escape from microfluidic channels, revealing a self-similar process with escape time inversely related to the last particle's diffusion coefficient, influenced by tiny bias forces, with implications for device design.

Contribution

The paper introduces a theoretical and experimental framework for quantifying escape times of particles from microchannels, highlighting the self-similar nature and the impact of minute bias forces.

Findings

Escape time scales inversely with the last particle's diffusion coefficient.

Tiny bias forces significantly reduce escape time by decreasing collisions.

The results guide the design of micro- and nano-devices for various applications.

Abstract

Single-file diffusion is a ubiquitous physical process exploited by living and synthetic systems to exchange molecules with their environment. It is paramount quantifying the escape time needed for single files of particles to exit from constraining synthetic channels and biological pores. This quantity depends on complex cooperative effects, whose predominance can only be established through a strict comparison between theory and experiments. By using colloidal particles, optical manipulation, microfluidics, digital microscopy and theoretical analysis we uncover the self-similar character of the escape process and provide closed-formula evaluations of the escape time. We find that the escape time scales inversely with the diffusion coefficient of the last particle to leave the channel. Importantly, we find that at the investigated {\bf microscale}, bias forces as tiny as $10^{-15}\;{\rm N}$ determine the magnitude of the escape time by drastically reducing interparticle collisions. Our findings provide crucial guidelines to optimize the design of micro- and nano-devices for a variety of applications including drug delivery, particle filtering and transport in geometrical constrictions.