Mixing Mechanism of Microfluidic Mixer with Staggered Virtual Electrode Based on Light-Actuated AC Electroosmosis.

Liuyong Shi,Teng Zhou,Xiangtao Zhong,Hanghang Ding,Zhenyu Liu,Binfeng Yin

doi:10.3390/mi12070744

Abstract

In this paper, we present a novel microfluidic mixer with staggered virtual electrode based on light-actuated AC electroosmosis (LACE). We solve the coupled system of the flow field described by Navier–Stokes equations, the described electric field by a Laplace equation, and the concentration field described by a convection–diffusion equation via a finite-element method (FEM). Moreover, we study the distribution of the flow, electric, and concentration fields in the microchannel, and reveal the generating mechanism of the rotating vortex on the cross-section of the microchannel and the mixing mechanism of the fluid sample. We also explore the influence of several key geometric parameters such as the length, width, and spacing of the virtual electrode, and the height of the microchannel on mixing performance; the relatively optimal mixer structure is thus obtained. The current micromixer provides a favorable fluid-mixing method based on an optical virtual electrode, and could promote the comprehensive integration of functions in modern microfluidic-analysis systems.

Highlights

Introduction and NamTrung NguyenMicromixing [1] is one of the key technologies of micro-total analysis systems [2]and lab-on-a-chip (LOC) [3] devices, and it is widely used in the fields of biology [4], chemistry [5], medicine [6], and engineering, both in academia and industry, because of its low cost, high speed, and low sample consumption [7,8,9]
The position of the virtual electrodes staggered along the axial direction of the microchannel is shown in Figure 1c, which clearly shows the characteristic size (Lc, W c ) of the microchannel, the characteristic size (Lo = 10 μm, W o = 10 μm, So = 10 μm, Do = 90 μm) of the staggered light spot projected onto the photoconductive layer, and the position of each section (A–A, B–B, C–C, D–D)
By giving the electric-field, flow-field, and concentration-distribution evolution of the A–A cross-section in the microchannel at five different moments during one electric-field cycle, we elaborate the effect of the staggered virtual electrodes on the fluid mixing and reveal its mixing mechanism

Summary

Introduction and Nam-Trung Nguyen

Micromixing [1] is one of the key technologies of micro-total analysis systems (μTAS) [2]. To improve the mixing efficiency of the micromixer by optimizing the size of the device and the time of sample analysis is the main object of the design and development of micromixers today. The rotating electroosmotic vortex generated under the action of applied potential is widely used in active micromixers to manipulate and control different fluids to achieve mixing. The mixer structure and mixing efficiency in [46] could still be further optimized and improved On this basis, we improved the inlet layout of the mixer and designed a new type of staggered electrode, further revealing the fluid-mixing mechanism under the combined action of the staggered electrode and the applied electric field by multiphysics field coupling numerical simulation. The influence of geometric parameters, including the length, width, and spacing of the staggered virtual electrodes, and the height of the microchannel, on mixing efficiency was studied (this is rarely mentioned in previous studies, and the circular spot or ring virtual electrode was generally employed before); a relatively optimal mixer structure was obtained

Micromixer Structure

Governing Equations

Mixing Process and Mechanism

Influence of Key Geometric Parameters on Mixing Performance

Conclusions