Electrokinetic Current Driven by a Viscosity Gradient

TL;DR

This paper reports a novel electrokinetic transport effect driven by viscosity gradients in nanofluidic channels, revealing fundamental behavior related to multiplicative noise and ionic current flow.

Contribution

It introduces the discovery of viscosity-gradient-driven ionic currents and provides a simple model explaining the underlying mechanism involving diffusivity gradients.

Findings

Viscosity gradients induce measurable ionic currents in nanofluidic channels.

The ionic current is explained by ions drifting due to local diffusivity gradients.

The effect is significant and relevant to various nanofluidic systems.

Abstract

Gradients of voltage, pressure, temperature, and salinity can transport objects in micro- and nanofluidic systems by well known mechanisms. Here we report the discovery of a transport effect driven by viscosity gradients, which cause an ionic current to flow inside a glass nanofluidic channel. Measurements of the current are well described by a simple model wherein counterions in the electric double layers near the surfaces drift in the direction of decreasing viscosity with a drift speed equal to the gradient of the ions' local diffusivity. Drift in a viscosity gradient is a consequence of multiplicative (state-dependent) noise, which results from a particle's thermal fluctuations depending on its position. This surprisingly large effect, measured in a highly controlled nanofluidic environment, reveals fundamental behavior that is relevant to a broad range of systems.