Onset of nonlinear electroosmotic flow under AC electric field

TL;DR

This study experimentally identifies the transition point from linear to nonlinear electroosmotic flow under AC electric fields using high-resolution velocity measurements, revealing a universal scaling law for the critical electric field.

Contribution

It introduces a novel experimental approach to study nonlinear EOF onset and establishes a generalized scaling law linking electric field, frequency, and velocity.

Findings

Critical electric field scales with frequency and velocity as E_{A,C}~f_f^{0.48-0.027U}

Velocity fluctuations distinguish linear and nonlinear EOF regimes

Universal control parameters accurately govern EOF behavior

Abstract

Nonlinearity of electroosmotic flows (EOFs) is ubiquitous and plays a crucial role in the mass and energy transfer in ion transport, specimen mixing, electrochemistry reaction, and electric energy storage and utilizing. When and how the transition from a linear regime to a nonlinear one is essential for understanding, prohibiting or utilizing nonlinear EOF. However, suffers the lacking of reliable experimental instruments with high spatial and temporal resolutions, the investigation of the onset of nonlinear EOF still stays in theory. Herein, we experimentally studied the velocity fluctuations of EOFs driven by AC electric field via ultra-sensitive fluorescent blinking tricks. The linear and nonlinear AC EOFs are successfully identified from both the time trace and energy spectra of velocity fluctuations. The critical electric field ($E_{A,C}$) separating the two statuses is determined and is discovered by defining a generalized scaling law with respect to the convection velocity ($U$) and AC frequency ($f_f$) as $E_{A,C}$~${f_f}^{0.48-0.027U}$. The universal control parameters are determined with surprising accuracy for governing the status of AC EOFs. We hope the current investigation could be essential in the development of both theory and applications of nonlinear EOF.