High-efficiency electrokinetic micromixing through symmetric sequential injection and expansion

Abstract

Rapid electric field switching is an established microfluidic mixing strategy for electrokinetic flows. Many such microfluidic mixers are variations on the T- or Y-form channel geometry. In these configurations, rapid switching of the electric field can greatly improve initial mixing over that achieved with static-field mixing. Due to a fundamental lack of symmetry, however, these strategies produce lingering cross-channel concentration gradients which delay complete mixing of the fluid stream. In this paper, a field switching microfluidic mixing strategy which utilizes a symmetric sequential injection geometry with an expansion chamber to achieve high efficiency microfluidic mixing is demonstrated experimentally. A three-inlet injector sequentially interlaces two dissimilar incoming solutions. Downstream of the injector, the sequence enters an expansion chamber resulting in a dramatic (two orders of magnitude) decrease in Peclet number and rapid axial diffusive mixing. The outlet concentration may be accurately varied over the full spectrum by tuning the duty cycle of the field switching waveform. The chips are designed with input from a previous numerical study, manufactured in poly(dimethylsiloxane) using soft-lithography based microfabrication, and tested using fluorescence microscopy. In the context of on-chip chemical processing for analytical operations, the demonstrated mixing strategy has several features: high mixing efficiency (99%), compact axial length (2.3 mm), steady outflow velocity, and readily variable outlet concentration (0.15 < c* < 0.95).

Integrated electrochemical velocimetry for microfluidic devices

“…The top part of the flow cell, containing the 100 lm high and 1 mm wide rectangular channel structure, was fabricated by replica molding in poly(dimethylsiloxane) (PDMS; Dow Corning, Midland, MI), following established soft-lithographic protocols (Duffy et al 1998). The specific equipment and procedure employed is detailed elsewhere (Coleman et al 2006). Holes for inlet and outlet tubing were punched in the PDMS prior to assembly.…”

Enhancement of electrokinetically driven microfluidic T‐mixer using frequency modulated electric field and channel geometry effects

“…Coleman and Sinton [19] developed a novel micromixing strategy and analyzed its performance numerically by exploiting the axial diffusion of a continuous sequence of discrete samples in a microchannel. Further, using rapid electric field switching, Coleman et al [20] fabricated a symmetry-based microfluidic mixer and provided an estimation of the preferred operating frequency range. Based on AC Faradaic polarization, Lastochkin et al [21] presented a micromixer design using AC EOF.…”

A Review on Mixing in Microfluidics

“…Like the hydrodynamic focusing method, the alternate-injection method also suffers from a fundamental drawback; the stirring occurs only in the inlet region of the channel. Although the larger chamber attached to the inlet channel proposed by Sinton's group [17,18], Leong et al [19] and Sun and Sie [20] promotes the mixing via the stretching of the slug, it is not like chaotic advection since the stretching occurs only linearly in time. Further, when elctroosmotic force is used for the fluid injection due to its feasibility in the injection control, bubble generation from the electrodes or the electrode degradation can cause another problem.…”

“…The research group of Sinton [17,18] conducted an experimental study on the mixing effect in a channel design composed of a cross inlet channel and a larger mixing chamber (Figure 9), where samples are sequentially injected via electroosmotic force. The decelerating flow in the expansion channel connected to the chamber makes the striation thinner and thinner, thus promoting the diffusion.…”