Bipolar nanochannels: The effects of an electro-osmotic instability. Part II: Time-transient response

TL;DR

This paper investigates the time-transient electro-osmotic response of bipolar nanochannels, revealing distinct behaviors from unipolar systems and providing insights into the dynamics of electroosmotic instability over time.

Contribution

It introduces a detailed analysis of the time-transient response of bipolar nanochannels, highlighting differences from unipolar systems and elucidating the governing principles of electroosmotic instability.

Findings

Bipolar systems can exhibit instability on both sides or none.

Instability in bipolar systems can vanish on one or both sides.

Time-transient behavior reveals principles distinct from steady-state analysis.

Abstract

The most common method to characterize the electrical response of a nanofluidic system is through its steady-state current-voltage response. In Part I, we demonstrated that this current-voltage response depends on the geometry, the layout of the surface charge, and the effects of advection. We demonstrated that each configuration has a unique steady-state signature. Here, we will elucidate the behavior of the time-transient response. Similar to the steady-state response, we will show that each configuration has its own unique time-transient signature when subjected to electroosmotic instability. We show that bipolar systems behave differently than unipolar systems. In unipolar systems, the instability appears only at one end of the system. In contrast, in bipolar systems the instability will either appear on both sides of the nanochannel or not at all. If it does appear on both sides, the instability will eventually vanish on one or both sides of the system. In Part I, these phenomena were explained using steady-state considerations of the behavior of the fluxes. Here, we will examine the time-transient behavior to reveal the governing principles that are, on the one hand, not so different from unipolar systems and, on the other hand, remarkably different.