Anomalously slow transport in single-file diffusion with slow binding kinetics

TL;DR

This study investigates how slow binding kinetics cause anomalously slow diffusion in single-file channels, revealing a scaling behavior of diffusivity and a unified understanding of subdiffusive dynamics.

Contribution

It introduces a simple cage-physics model that captures the scaling collapse of diffusivity and links subdiffusive behavior to transport properties in single-file diffusion with slow binding.

Findings

Slow binding kinetics lead to anomalously slow diffusion.

Diffusivity exhibits scaling collapse with respect to occupation fraction.

Subdiffusive behavior is governed by the same scaled diffusivity.

Abstract

We computationally study the effects of binding kinetics to the channel wall, leading to transient immobility, on the diffusive transport of particles within narrow channels, that exhibit single-file diffusion (SFD). We find that slow binding kinetics leads to an anomalously slow diffusive transport. Remarkably, the scaled diffusivity $\hat{D}$ characterizing transport exhibits scaling collapse with respect to the occupation fraction $p$ of sites along the channel. We present a simple "cage-physics" picture that captures the characteristic occupation fraction $p_{scale}$ and the asymptotic $1/p^2$ behavior for $p/p_{scale} \gtrsim 1$. We confirm that subdiffusive behavior of tracer particles is controlled by the same $\hat{D}$ as particle transport.